Assimilate ExtUtils::Constant 0.16

p4raw-id: //depot/perl@23867

4 files changed, 1365 insertions, 993 deletions

diff --git a/lib/ExtUtils/Constant.pm b/lib/ExtUtils/Constant.pm
index 1bd87177f4..00f5b42e45 100644
--- a/lib/ExtUtils/Constant.pm
+++ b/lib/ExtUtils/Constant.pm
@@ -1,6 +1,6 @@
 package ExtUtils::Constant;
-use vars qw (@ISA $VERSION %XS_Constant %XS_TypeSet @EXPORT_OK %EXPORT_TAGS);
-$VERSION = 0.15;
+use vars qw (@ISA $VERSION @EXPORT_OK %EXPORT_TAGS);
+$VERSION = 0.16;
 
 =head1 NAME
 
@@ -94,15 +94,11 @@ if ($] >= 5.006) {
   eval "use warnings; 1" or die $@;
 }
 use strict;
-use vars '$is_perl56';
-use Carp;
-
-$is_perl56 = ($] < 5.007 && $] > 5.005_50);
+use Carp qw(croak cluck);
 
 use Exporter;
-use Text::Wrap;
-$Text::Wrap::huge = 'overflow';
-$Text::Wrap::columns = 80;
+use ExtUtils::Constant::Utils qw(C_stringify);
+use ExtUtils::Constant::XS qw(%XS_Constant %XS_TypeSet);
 
 @ISA = 'Exporter';
 
@@ -113,117 +109,6 @@ $Text::Wrap::columns = 80;
 
 @EXPORT_OK = ( @{ $EXPORT_TAGS{'all'} } );
 
-# '' is used as a flag to indicate non-ascii macro names, and hence the need
-# to pass in the utf8 on/off flag.
-%XS_Constant = (
-		''    => '',
-		IV    => 'PUSHi(iv)',
-		UV    => 'PUSHu((UV)iv)',
-		NV    => 'PUSHn(nv)',
-		PV    => 'PUSHp(pv, strlen(pv))',
-		PVN   => 'PUSHp(pv, iv)',
-		SV    => 'PUSHs(sv)',
-		YES   => 'PUSHs(&PL_sv_yes)',
-		NO    => 'PUSHs(&PL_sv_no)',
-		UNDEF => '',	# implicit undef
-);
-
-%XS_TypeSet = (
-		IV    => '*iv_return =',
-		UV    => '*iv_return = (IV)',
-		NV    => '*nv_return =',
-		PV    => '*pv_return =',
-		PVN   => ['*pv_return =', '*iv_return = (IV)'],
-		SV    => '*sv_return = ',
-		YES   => undef,
-		NO    => undef,
-		UNDEF => undef,
-);
-
-
-=item C_stringify NAME
-
-A function which returns a 7 bit ASCII correctly \ escaped version of the
-string passed suitable for C's "" or ''. It will die if passed Unicode
-characters.
-
-=cut
-
-# Hopefully make a happy C identifier.
-sub C_stringify {
-  local $_ = shift;
-  return unless defined $_;
-  # grr 5.6.1
-  confess "Wide character in '$_' intended as a C identifier"
-    if tr/\0-\377// != length;
-  # grr 5.6.1 moreso because its regexps will break on data that happens to
-  # be utf8, which includes my 8 bit test cases.
-  $_ = pack 'C*', unpack 'U*', $_ . pack 'U*' if $is_perl56;
-  s/\\/\\\\/g;
-  s/([\"\'])/\\$1/g;	# Grr. fix perl mode.
-  s/\n/\\n/g;		# Ensure newlines don't end up in octal
-  s/\r/\\r/g;
-  s/\t/\\t/g;
-  s/\f/\\f/g;
-  s/\a/\\a/g;
-  s/([^\0-\177])/sprintf "\\%03o", ord $1/ge;
-  unless ($] < 5.006) {
-    # This will elicit a warning on 5.005_03 about [: :] being reserved unless
-    # I cheat
-    my $cheat = '([[:^print:]])';
-    s/$cheat/sprintf "\\%03o", ord $1/ge;
-  } else {
-    require POSIX;
-    s/([^A-Za-z0-9_])/POSIX::isprint($1) ? $1 : sprintf "\\%03o", ord $1/ge;
-  }
-  $_;
-}
-
-=item perl_stringify NAME
-
-A function which returns a 7 bit ASCII correctly \ escaped version of the
-string passed suitable for a perl "" string.
-
-=cut
-
-# Hopefully make a happy perl identifier.
-sub perl_stringify {
-  local $_ = shift;
-  return unless defined $_;
-  s/\\/\\\\/g;
-  s/([\"\'])/\\$1/g;	# Grr. fix perl mode.
-  s/\n/\\n/g;		# Ensure newlines don't end up in octal
-  s/\r/\\r/g;
-  s/\t/\\t/g;
-  s/\f/\\f/g;
-  s/\a/\\a/g;
-  unless ($] < 5.006) {
-    if ($] > 5.007) {
-      s/([^\0-\177])/sprintf "\\x{%X}", ord $1/ge;
-    } else {
-      # Grr 5.6.1. And I don't think I can use utf8; to force the regexp
-      # because 5.005_03 will fail.
-      # This is grim, but I also can't split on //
-      my $copy;
-      foreach my $index (0 .. length ($_) - 1) {
-        my $char = substr ($_, $index, 1);
-        $copy .= ($char le "\177") ? $char : sprintf "\\x{%X}", ord $char;
-      }
-      $_ = $copy;
-    }
-    # This will elicit a warning on 5.005_03 about [: :] being reserved unless
-    # I cheat
-    my $cheat = '([[:^print:]])';
-    s/$cheat/sprintf "\\%03o", ord $1/ge;
-  } else {
-    # Turns out "\x{}" notation only arrived with 5.6
-    s/([^\0-\177])/sprintf "\\x%02X", ord $1/ge;
-    require POSIX;
-    s/([^A-Za-z0-9_])/POSIX::isprint($1) ? $1 : sprintf "\\%03o", ord $1/ge;
-  }
-  $_;
-}
-
 =item constant_types
 
 A function returning a single scalar with C<#define> definitions for the
@@ -231,865 +116,37 @@ constants used internally between the generated C and XS functions.
 
 =cut
 
-sub constant_types () {
-  my $start = 1;
-  my @lines;
-  push @lines, "#define PERL_constant_NOTFOUND\t$start\n"; $start++;
-  push @lines, "#define PERL_constant_NOTDEF\t$start\n"; $start++;
-  foreach (sort keys %XS_Constant) {
-    next if $_ eq '';
-    push @lines, "#define PERL_constant_IS$_\t$start\n"; $start++;
-  }
-  push @lines, << 'EOT';
-
-#ifndef NVTYPE
-typedef double NV; /* 5.6 and later define NVTYPE, and typedef NV to it.  */
-#endif
-#ifndef aTHX_
-#define aTHX_ /* 5.6 or later define this for threading support.  */
-#endif
-#ifndef pTHX_
-#define pTHX_ /* 5.6 or later define this for threading support.  */
-#endif
-EOT
-
-  return join '', @lines;
+sub constant_types {
+  ExtUtils::Constant::XS->header();
 }
 
-=item memEQ_clause NAME, CHECKED_AT, INDENT
-
-A function to return a suitable C C<if> statement to check whether I<NAME>
-is equal to the C variable C<name>. If I<CHECKED_AT> is defined, then it
-is used to avoid C<memEQ> for short names, or to generate a comment to
-highlight the position of the character in the C<switch> statement.
-
-If I<CHECKED_AT> is a reference to a scalar, then instead it gives
-the characters pre-checked at the beginning, (and the number of chars by
-which the C variable name has been advanced. These need to be chopped from
-the front of I<NAME>).
-
-=cut
-
 sub memEQ_clause {
-#    if (memEQ(name, "thingy", 6)) {
-  # Which could actually be a character comparison or even ""
-  my ($name, $checked_at, $indent) = @_;
-  $indent = ' ' x ($indent || 4);
-  my $front_chop;
-  if (ref $checked_at) {
-    # regexp won't work on 5.6.1 without use utf8; in turn that won't work
-    # on 5.005_03.
-    substr ($name, 0, length $$checked_at,) = '';
-    $front_chop = C_stringify ($$checked_at);
-    undef $checked_at;
-  }
-  my $len = length $name;
-
-  if ($len < 2) {
-    return $indent . "{\n"
-	if (defined $checked_at and $checked_at == 0) or $len == 0;
-    # We didn't switch, drop through to the code for the 2 character string
-    $checked_at = 1;
-  }
-  if ($len < 3 and defined $checked_at) {
-    my $check;
-    if ($checked_at == 1) {
-      $check = 0;
-    } elsif ($checked_at == 0) {
-      $check = 1;
-    }
-    if (defined $check) {
-      my $char = C_stringify (substr $name, $check, 1);
-      return $indent . "if (name[$check] == '$char') {\n";
-    }
-  }
-  if (($len == 2 and !defined $checked_at)
-     or ($len == 3 and defined ($checked_at) and $checked_at == 2)) {
-    my $char1 = C_stringify (substr $name, 0, 1);
-    my $char2 = C_stringify (substr $name, 1, 1);
-    return $indent . "if (name[0] == '$char1' && name[1] == '$char2') {\n";
-  }
-  if (($len == 3 and defined ($checked_at) and $checked_at == 1)) {
-    my $char1 = C_stringify (substr $name, 0, 1);
-    my $char2 = C_stringify (substr $name, 2, 1);
-    return $indent . "if (name[0] == '$char1' && name[2] == '$char2') {\n";
-  }
-
-  my $pointer = '^';
-  my $have_checked_last = defined ($checked_at) && $len == $checked_at + 1;
-  if ($have_checked_last) {
-    # Checked at the last character, so no need to memEQ it.
-    $pointer = C_stringify (chop $name);
-    $len--;
-  }
-
-  $name = C_stringify ($name);
-  my $body = $indent . "if (memEQ(name, \"$name\", $len)) {\n";
-  # Put a little ^ under the letter we checked at
-  # Screws up for non printable and non-7 bit stuff, but that's too hard to
-  # get right.
-  if (defined $checked_at) {
-    $body .= $indent . "/*               ". (' ' x $checked_at) . $pointer
-      . (' ' x ($len - $checked_at + length $len)) . "    */\n";
-  } elsif (defined $front_chop) {
-    $body .= $indent . "/*              $front_chop"
-      . (' ' x ($len + 1 + length $len)) . "    */\n";
-  }
-  return $body;
+  cluck "ExtUtils::Constant::memEQ_clause is deprecated";
+  ExtUtils::Constant::XS->memEQ_clause({name=>$_[0], checked_at=>$_[1],
+					indent=>$_[2]});
 }
 
-=item assign INDENT, TYPE, PRE, POST, VALUE...
-
-A function to return a suitable assignment clause. If I<TYPE> is aggregate
-(eg I<PVN> expects both pointer and length) then there should be multiple
-I<VALUE>s for the components. I<PRE> and I<POST> if defined give snippets
-of C code to proceed and follow the assignment. I<PRE> will be at the start
-of a block, so variables may be defined in it.
-
-=cut
-
-# Hmm. value undef to to NOTDEF? value () to do NOTFOUND?
-
-sub assign {
-  my $indent = shift;
-  my $type = shift;
-  my $pre = shift;
-  my $post = shift || '';
-  my $clause;
-  my $close;
-  if ($pre) {
-    chomp $pre;
-    $clause = $indent . "{\n$pre";
-    $clause .= ";" unless $pre =~ /;$/;
-    $clause .= "\n";
-    $close = "$indent}\n";
-    $indent .= "  ";
-  }
-  confess "undef \$type" unless defined $type;
-  confess "Can't generate code for type $type" unless exists $XS_TypeSet{$type};
-  my $typeset = $XS_TypeSet{$type};
-  if (ref $typeset) {
-    die "Type $type is aggregate, but only single value given"
-      if @_ == 1;
-    foreach (0 .. $#$typeset) {
-      $clause .= $indent . "$typeset->[$_] $_[$_];\n";
-    }
-  } elsif (defined $typeset) {
-    die "Aggregate value given for type $type"
-      if @_ > 1;
-    $clause .= $indent . "$typeset $_[0];\n";
-  }
-  chomp $post;
-  if (length $post) {
-    $clause .= "$post";
-    $clause .= ";" unless $post =~ /;$/;
-    $clause .= "\n";
-  }
-  $clause .= "${indent}return PERL_constant_IS$type;\n";
-  $clause .= $close if $close;
-  return $clause;
-}
-
-=item return_clause
-
-return_clause ITEM, INDENT
-
-A function to return a suitable C<#ifdef> clause. I<ITEM> is a hashref
-(as passed to C<C_constant> and C<match_clause>. I<INDENT> is the number
-of spaces to indent, defaulting to 6.
-
-=cut
-
 sub return_clause ($$) {
-##ifdef thingy
-#      *iv_return = thingy;
-#      return PERL_constant_ISIV;
-##else
-#      return PERL_constant_NOTDEF;
-##endif
-  my ($item, $indent) = @_;
-
-  my ($name, $value, $macro, $default, $pre, $post, $def_pre, $def_post, $type)
-    = @$item{qw (name value macro default pre post def_pre def_post type)};
-  $value = $name unless defined $value;
-  $macro = $name unless defined $macro;
-
-  $macro = $value unless defined $macro;
-  $indent = ' ' x ($indent || 6);
-  unless ($type) {
-    # use Data::Dumper; print STDERR Dumper ($item);
-    confess "undef \$type";
-  }
-
-  my $clause;
-
-  ##ifdef thingy
-  if (ref $macro) {
-    $clause = $macro->[0];
-  } elsif ($macro ne "1") {
-    $clause = "#ifdef $macro\n";
-  }
-
-  #      *iv_return = thingy;
-  #      return PERL_constant_ISIV;
-  $clause .= assign ($indent, $type, $pre, $post,
-                     ref $value ? @$value : $value);
-
-  if (ref $macro or $macro ne "1") {
-    ##else
-    $clause .= "#else\n";
-
-    #      return PERL_constant_NOTDEF;
-    if (!defined $default) {
-      $clause .= "${indent}return PERL_constant_NOTDEF;\n";
-    } else {
-      my @default = ref $default ? @$default : $default;
-      $type = shift @default;
-      $clause .= assign ($indent, $type, $def_pre, $def_post, @default);
-    }
-
-    ##endif
-    if (ref $macro) {
-      $clause .= $macro->[1];
-    } else {
-      $clause .= "#endif\n";
-    }
-  }
-  return $clause;
-}
-
-=pod
-
-XXX document me
-
-=cut
-
-sub match_clause {
-  # $offset defined if we have checked an offset.
-  my ($item, $offset, $indent) = @_;
-  $indent = ' ' x ($indent || 4);
-  my $body = '';
-  my ($no, $yes, $either, $name, $inner_indent);
-  if (ref $item eq 'ARRAY') {
-    ($yes, $no) = @$item;
-    $either = $yes || $no;
-    confess "$item is $either expecting hashref in [0] || [1]"
-      unless ref $either eq 'HASH';
-    $name = $either->{name};
-  } else {
-    confess "$item->{name} has utf8 flag '$item->{utf8}', should be false"
-      if $item->{utf8};
-    $name = $item->{name};
-    $inner_indent = $indent;
-  }
-
-  $body .= memEQ_clause ($name, $offset, length $indent);
-  if ($yes) {
-    $body .= $indent . "  if (utf8) {\n";
-  } elsif ($no) {
-    $body .= $indent . "  if (!utf8) {\n";
-  }
-  if ($either) {
-    $body .= return_clause ($either, 4 + length $indent);
-    if ($yes and $no) {
-      $body .= $indent . "  } else {\n";
-      $body .= return_clause ($no, 4 + length $indent); 
-    }
-    $body .= $indent . "  }\n";
-  } else {
-    $body .= return_clause ($item, 2 + length $indent);
-  }
-  $body .= $indent . "}\n";
+  cluck "ExtUtils::Constant::return_clause is deprecated";
+  my $indent = shift;
+  ExtUtils::Constant::XS->return_clause({indent=>$indent}, @_);
 }
 
-=item switch_clause INDENT, NAMELEN, ITEMHASH, ITEM...
-
-An internal function to generate a suitable C<switch> clause, called by
-C<C_constant> I<ITEM>s are in the hash ref format as given in the description
-of C<C_constant>, and must all have the names of the same length, given by
-I<NAMELEN> (This is not checked).  I<ITEMHASH> is a reference to a hash,
-keyed by name, values being the hashrefs in the I<ITEM> list.
-(No parameters are modified, and there can be keys in the I<ITEMHASH> that
-are not in the list of I<ITEM>s without causing problems).
-
-=cut
-
 sub switch_clause {
-  my ($indent, $comment, $namelen, $items, @items) = @_;
-  $indent = ' ' x ($indent || 2);
-
-  my @names = sort map {$_->{name}} @items;
-  my $leader = $indent . '/* ';
-  my $follower = ' ' x length $leader;
-  my $body = $indent . "/* Names all of length $namelen.  */\n";
-  if ($comment) {
-    $body = wrap ($leader, $follower, $comment) . "\n";
-    $leader = $follower;
-  }
-  my @safe_names = @names;
-  foreach (@safe_names) {
-    confess sprintf "Name '$_' is length %d, not $namelen", length
-      unless length == $namelen;
-    # Argh. 5.6.1
-    # next unless tr/A-Za-z0-9_//c;
-    next if tr/A-Za-z0-9_// == length;
-    $_ = '"' . perl_stringify ($_) . '"';
-    # Ensure that the enclosing C comment doesn't end
-    # by turning */  into *" . "/
-    s!\*\/!\*"."/!gs;
-    # gcc -Wall doesn't like finding /* inside a comment
-    s!\/\*!/"."\*!gs;
-  }
-  $body .= wrap ($leader, $follower, join (" ", @safe_names) . " */") . "\n";
-  # Figure out what to switch on.
-  # (RMS, Spread of jump table, Position, Hashref)
-  my @best = (1e38, ~0);
-  # Prefer the last character over the others. (As it lets us shortern the
-  # memEQ clause at no cost).
-  foreach my $i ($namelen - 1, 0 .. ($namelen - 2)) {
-    my ($min, $max) = (~0, 0);
-    my %spread;
-    if ($is_perl56) {
-      # Need proper Unicode preserving hash keys for bytes in range 128-255
-      # here too, for some reason. grr 5.6.1 yet again.
-      tie %spread, 'ExtUtils::Constant::Aaargh56Hash';
-    }
-    foreach (@names) {
-      my $char = substr $_, $i, 1;
-      my $ord = ord $char;
-      confess "char $ord is out of range" if $ord > 255;
-      $max = $ord if $ord > $max;
-      $min = $ord if $ord < $min;
-      push @{$spread{$char}}, $_;
-      # warn "$_ $char";
-    }
-    # I'm going to pick the character to split on that minimises the root
-    # mean square of the number of names in each case. Normally this should
-    # be the one with the most keys, but it may pick a 7 where the 8 has
-    # one long linear search. I'm not sure if RMS or just sum of squares is
-    # actually better.
-    # $max and $min are for the tie-breaker if the root mean squares match.
-    # Assuming that the compiler may be building a jump table for the
-    # switch() then try to minimise the size of that jump table.
-    # Finally use < not <= so that if it still ties the earliest part of
-    # the string wins. Because if that passes but the memEQ fails, it may
-    # only need the start of the string to bin the choice.
-    # I think. But I'm micro-optimising. :-)
-    # OK. Trump that. Now favour the last character of the string, before the
-    # rest.
-    my $ss;
-    $ss += @$_ * @$_ foreach values %spread;
-    my $rms = sqrt ($ss / keys %spread);
-    if ($rms < $best[0] || ($rms == $best[0] && ($max - $min) < $best[1])) {
-      @best = ($rms, $max - $min, $i, \%spread);
-    }
-  }
-  confess "Internal error. Failed to pick a switch point for @names"
-    unless defined $best[2];
-  # use Data::Dumper; print Dumper (@best);
-  my ($offset, $best) = @best[2,3];
-  $body .= $indent . "/* Offset $offset gives the best switch position.  */\n";
-
-  my $do_front_chop = $offset == 0 && $namelen > 2;
-  if ($do_front_chop) {
-    $body .= $indent . "switch (*name++) {\n";
-  } else {
-    $body .= $indent . "switch (name[$offset]) {\n";
-  }
-  foreach my $char (sort keys %$best) {
-    confess sprintf "'$char' is %d bytes long, not 1", length $char
-      if length ($char) != 1;
-    confess sprintf "char %#X is out of range", ord $char if ord ($char) > 255;
-    $body .= $indent . "case '" . C_stringify ($char) . "':\n";
-    foreach my $name (sort @{$best->{$char}}) {
-      my $thisone = $items->{$name};
-      # warn "You are here";
-      if ($do_front_chop) {
-        $body .= match_clause ($thisone, \$char, 2 + length $indent);
-      } else {
-        $body .= match_clause ($thisone, $offset, 2 + length $indent);
-      }
-    }
-    $body .= $indent . "  break;\n";
-  }
-  $body .= $indent . "}\n";
-  return $body;
-}
-
-=item params WHAT
-
-An internal function. I<WHAT> should be a hashref of types the constant
-function will return. I<params> returns a hashref keyed IV NV PV SV to show
-which combination of pointers will be needed in the C argument list.
-
-=cut
-
-sub params {
-  my $what = shift;
-  foreach (sort keys %$what) {
-    warn "ExtUtils::Constant doesn't know how to handle values of type $_" unless defined $XS_Constant{$_};
-  }
-  my $params = {};
-  $params->{''} = 1 if $what->{''};
-  $params->{IV} = 1 if $what->{IV} || $what->{UV} || $what->{PVN};
-  $params->{NV} = 1 if $what->{NV};
-  $params->{PV} = 1 if $what->{PV} || $what->{PVN};
-  $params->{SV} = 1 if $what->{SV};
-  return $params;
-}
-
-=item dump_names
-
-dump_names DEFAULT_TYPE, TYPES, INDENT, OPTIONS, ITEM...
-
-An internal function to generate the embedded perl code that will regenerate
-the constant subroutines.  I<DEFAULT_TYPE>, I<TYPES> and I<ITEM>s are the
-same as for C_constant.  I<INDENT> is treated as number of spaces to indent
-by.  I<OPTIONS> is a hashref of options. Currently only C<declare_types> is
-recognised.  If the value is true a C<$types> is always declared in the perl
-code generated, if defined and false never declared, and if undefined C<$types>
-is only declared if the values in I<TYPES> as passed in cannot be inferred from
-I<DEFAULT_TYPES> and the I<ITEM>s.
-
-=cut
-
-sub dump_names {
-  my ($default_type, $what, $indent, $options, @items) = @_;
-  my $declare_types = $options->{declare_types};
-  $indent = ' ' x ($indent || 0);
-
-  my $result;
-  my (@simple, @complex, %used_types);
-  foreach (@items) {
-    my $type;
-    if (ref $_) {
-      $type = $_->{type} || $default_type;
-      if ($_->{utf8}) {
-        # For simplicity always skip the bytes case, and reconstitute this entry
-        # from its utf8 twin.
-        next if $_->{utf8} eq 'no';
-        # Copy the hashref, as we don't want to mess with the caller's hashref.
-        $_ = {%$_};
-        unless ($is_perl56) {
-          utf8::decode ($_->{name});
-        } else {
-          $_->{name} = pack 'U*', unpack 'U0U*', $_->{name};
-        }
-        delete $_->{utf8};
-      }
-    } else {
-      $_ = {name=>$_};
-      $type = $default_type;
-    }
-    $used_types{$type}++;
-    if ($type eq $default_type
-        # grr 5.6.1
-        and length $_->{name}
-        and length $_->{name} == ($_->{name} =~ tr/A-Za-z0-9_//)
-        and !defined ($_->{macro}) and !defined ($_->{value})
-        and !defined ($_->{default}) and !defined ($_->{pre})
-        and !defined ($_->{post}) and !defined ($_->{def_pre})
-        and !defined ($_->{def_post})) {
-      # It's the default type, and the name consists only of A-Za-z0-9_
-      push @simple, $_->{name};
-    } else {
-      push @complex, $_;
-    }
-  }
-
-  if (!defined $declare_types) {
-    # Do they pass in any types we weren't already using?
-    foreach (keys %$what) {
-      next if $used_types{$_};
-      $declare_types++; # Found one in $what that wasn't used.
-      last; # And one is enough to terminate this loop
-    }
-  }
-  if ($declare_types) {
-    $result = $indent . 'my $types = {map {($_, 1)} qw('
-      . join (" ", sort keys %$what) . ")};\n";
-  }
-  $result .= wrap ($indent . "my \@names = (qw(",
-		   $indent . "               ", join (" ", sort @simple) . ")");
-  if (@complex) {
-    foreach my $item (sort {$a->{name} cmp $b->{name}} @complex) {
-      my $name = perl_stringify $item->{name};
-      my $line = ",\n$indent            {name=>\"$name\"";
-      $line .= ", type=>\"$item->{type}\"" if defined $item->{type};
-      foreach my $thing (qw (macro value default pre post def_pre def_post)) {
-        my $value = $item->{$thing};
-        if (defined $value) {
-          if (ref $value) {
-            $line .= ", $thing=>[\""
-              . join ('", "', map {perl_stringify $_} @$value) . '"]';
-          } else {
-            $line .= ", $thing=>\"" . perl_stringify($value) . "\"";
-          }
-        }
-      }
-      $line .= "}";
-      # Ensure that the enclosing C comment doesn't end
-      # by turning */  into *" . "/
-      $line =~ s!\*\/!\*" . "/!gs;
-      # gcc -Wall doesn't like finding /* inside a comment
-      $line =~ s!\/\*!/" . "\*!gs;
-      $result .= $line;
-    }
-  }
-  $result .= ");\n";
-
-  $result;
-}
-
-
-=item dogfood
-
-dogfood PACKAGE, SUBNAME, DEFAULT_TYPE, TYPES, INDENT, BREAKOUT, ITEM...
-
-An internal function to generate the embedded perl code that will regenerate
-the constant subroutines.  Parameters are the same as for C_constant.
-
-=cut
-
-sub dogfood {
-  my ($package, $subname, $default_type, $what, $indent, $breakout, @items)
-    = @_;
-  my $result = <<"EOT";
-  /* When generated this function returned values for the list of names given
-     in this section of perl code.  Rather than manually editing these functions
-     to add or remove constants, which would result in this comment and section
-     of code becoming inaccurate, we recommend that you edit this section of
-     code, and use it to regenerate a new set of constant functions which you
-     then use to replace the originals.
-
-     Regenerate these constant functions by feeding this entire source file to
-     perl -x
-
-#!$^X -w
-use ExtUtils::Constant qw (constant_types C_constant XS_constant);
-
-EOT
-  $result .= dump_names ($default_type, $what, 0, {declare_types=>1}, @items);
-  $result .= <<'EOT';
-
-print constant_types(); # macro defs
-EOT
-  $package = perl_stringify($package);
-  $result .=
-    "foreach (C_constant (\"$package\", '$subname', '$default_type', \$types, ";
-  # The form of the indent parameter isn't defined. (Yet)
-  if (defined $indent) {
-    require Data::Dumper;
-    $Data::Dumper::Terse=1;
-    $Data::Dumper::Terse=1; # Not used once. :-)
-    chomp ($indent = Data::Dumper::Dumper ($indent));
-    $result .= $indent;
-  } else {
-    $result .= 'undef';
-  }
-  $result .= ", $breakout" . ', @names) ) {
-    print $_, "\n"; # C constant subs
-}
-print "#### XS Section:\n";
-print XS_constant ("' . $package . '", $types);
-__END__
-   */
-
-';
-
-  $result;
+  cluck "ExtUtils::Constant::switch_clause is deprecated";
+  my $indent = shift;
+  my $comment = shift;
+  ExtUtils::Constant::XS->switch_clause({indent=>$indent, comment=>$comment},
+					@_);
 }
 
-=item C_constant
-
-C_constant PACKAGE, SUBNAME, DEFAULT_TYPE, TYPES, INDENT, BREAKOUT, ITEM...
-
-A function that returns a B<list> of C subroutine definitions that return
-the value and type of constants when passed the name by the XS wrapper.
-I<ITEM...> gives a list of constant names. Each can either be a string,
-which is taken as a C macro name, or a reference to a hash with the following
-keys
-
-=over 8
-
-=item name
-
-The name of the constant, as seen by the perl code.
-
-=item type
-
-The type of the constant (I<IV>, I<NV> etc)
-
-=item value
-
-A C expression for the value of the constant, or a list of C expressions if
-the type is aggregate. This defaults to the I<name> if not given.
-
-=item macro
-
-The C pre-processor macro to use in the C<#ifdef>. This defaults to the
-I<name>, and is mainly used if I<value> is an C<enum>. If a reference an
-array is passed then the first element is used in place of the C<#ifdef>
-line, and the second element in place of the C<#endif>. This allows
-pre-processor constructions such as
-
-    #if defined (foo)
-    #if !defined (bar)
-    ...
-    #endif
-    #endif
-
-to be used to determine if a constant is to be defined.
-
-A "macro" 1 signals that the constant is always defined, so the C<#if>/C<#endif>
-test is omitted.
-
-=item default
-
-Default value to use (instead of C<croak>ing with "your vendor has not
-defined...") to return if the macro isn't defined. Specify a reference to
-an array with type followed by value(s).
-
-=item pre
-
-C code to use before the assignment of the value of the constant. This allows
-you to use temporary variables to extract a value from part of a C<struct>
-and return this as I<value>. This C code is places at the start of a block,
-so you can declare variables in it.
-
-=item post
-
-C code to place between the assignment of value (to a temporary) and the
-return from the function. This allows you to clear up anything in I<pre>.
-Rarely needed.
-
-=item def_pre
-=item def_post
-
-Equivalents of I<pre> and I<post> for the default value.
-
-=item utf8
-
-Generated internally. Is zero or undefined if name is 7 bit ASCII,
-"no" if the name is 8 bit (and so should only match if SvUTF8() is false),
-"yes" if the name is utf8 encoded.
-
-The internals automatically clone any name with characters 128-255 but none
-256+ (ie one that could be either in bytes or utf8) into a second entry
-which is utf8 encoded.
-
-=back
-
-I<PACKAGE> is the name of the package, and is only used in comments inside the
-generated C code.
-
-The next 5 arguments can safely be given as C<undef>, and are mainly used
-for recursion. I<SUBNAME> defaults to C<constant> if undefined.
-
-I<DEFAULT_TYPE> is the type returned by C<ITEM>s that don't specify their
-type. In turn it defaults to I<IV>. I<TYPES> should be given either as a comma
-separated list of types that the C subroutine C<constant> will generate or as
-a reference to a hash. I<DEFAULT_TYPE> will be added to the list if not
-present, as will any types given in the list of I<ITEM>s. The resultant list
-should be the same list of types that C<XS_constant> is given. [Otherwise
-C<XS_constant> and C<C_constant> may differ in the number of parameters to the
-constant function. I<INDENT> is currently unused and ignored. In future it may
-be used to pass in information used to change the C indentation style used.]
-The best way to maintain consistency is to pass in a hash reference and let
-this function update it.
-
-I<BREAKOUT> governs when child functions of I<SUBNAME> are generated.  If there
-are I<BREAKOUT> or more I<ITEM>s with the same length of name, then the code
-to switch between them is placed into a function named I<SUBNAME>_I<LEN>, for
-example C<constant_5> for names 5 characters long.  The default I<BREAKOUT> is
-3.  A single C<ITEM> is always inlined.
-
-=cut
-
-# The parameter now BREAKOUT was previously documented as:
-#
-# I<NAMELEN> if defined signals that all the I<name>s of the I<ITEM>s are of
-# this length, and that the constant name passed in by perl is checked and
-# also of this length. It is used during recursion, and should be C<undef>
-# unless the caller has checked all the lengths during code generation, and
-# the generated subroutine is only to be called with a name of this length.
-#
-# As you can see it now performs this function during recursion by being a
-# scalar reference.
-
 sub C_constant {
   my ($package, $subname, $default_type, $what, $indent, $breakout, @items)
     = @_;
-  $package ||= 'Foo';
-  $subname ||= 'constant';
-  # I'm not using this. But a hashref could be used for full formatting without
-  # breaking this API
-  # $indent ||= 0;
-
-  my ($namelen, $items);
-  if (ref $breakout) {
-    # We are called recursively. We trust @items to be normalised, $what to
-    # be a hashref, and pinch %$items from our parent to save recalculation.
-    ($namelen, $items) = @$breakout;
-  } else {
-    if ($is_perl56) {
-      # Need proper Unicode preserving hash keys.
-      $items = {};
-      tie %$items, 'ExtUtils::Constant::Aaargh56Hash';
-    }
-    $breakout ||= 3;
-    $default_type ||= 'IV';
-    if (!ref $what) {
-      # Convert line of the form IV,UV,NV to hash
-      $what = {map {$_ => 1} split /,\s*/, ($what || '')};
-      # Figure out what types we're dealing with, and assign all unknowns to the
-      # default type
-    }
-    my @new_items;
-    foreach my $orig (@items) {
-      my ($name, $item);
-      if (ref $orig) {
-        # Make a copy which is a normalised version of the ref passed in.
-        $name = $orig->{name};
-        my ($type, $macro, $value) = @$orig{qw (type macro value)};
-        $type ||= $default_type;
-        $what->{$type} = 1;
-        $item = {name=>$name, type=>$type};
-
-        undef $macro if defined $macro and $macro eq $name;
-        $item->{macro} = $macro if defined $macro;
-        undef $value if defined $value and $value eq $name;
-        $item->{value} = $value if defined $value;
-        foreach my $key (qw(default pre post def_pre def_post)) {
-          my $value = $orig->{$key};
-          $item->{$key} = $value if defined $value;
-          # warn "$key $value";
-        }
-      } else {
-        $name = $orig;
-        $item = {name=>$name, type=>$default_type};
-        $what->{$default_type} = 1;
-      }
-      warn "ExtUtils::Constant doesn't know how to handle values of type $_ used in macro $name" unless defined $XS_Constant{$item->{type}};
-      # tr///c is broken on 5.6.1 for utf8, so my original tr/\0-\177//c
-      # doesn't work. Upgrade to 5.8
-      # if ($name !~ tr/\0-\177//c || $] < 5.005_50) {
-      if ($name =~ tr/\0-\177// == length $name || $] < 5.005_50) {
-        # No characters outside 7 bit ASCII.
-        if (exists $items->{$name}) {
-          die "Multiple definitions for macro $name";
-        }
-        $items->{$name} = $item;
-      } else {
-        # No characters outside 8 bit. This is hardest.
-        if (exists $items->{$name} and ref $items->{$name} ne 'ARRAY') {
-          confess "Unexpected ASCII definition for macro $name";
-        }
-        # Again, 5.6.1 tr broken, so s/5\.6.*/5\.8\.0/;
-        # if ($name !~ tr/\0-\377//c) {
-        if ($name =~ tr/\0-\377// == length $name) {
-#          if ($] < 5.007) {
-#            $name = pack "C*", unpack "U*", $name;
-#          }
-          $item->{utf8} = 'no';
-          $items->{$name}[1] = $item;
-          push @new_items, $item;
-          # Copy item, to create the utf8 variant.
-          $item = {%$item};
-        }
-        # Encode the name as utf8 bytes.
-        unless ($is_perl56) {
-          utf8::encode($name);
-        } else {
-#          warn "Was >$name< " . length ${name};
-          $name = pack 'C*', unpack 'C*', $name . pack 'U*';
-#          warn "Now '${name}' " . length ${name};
-        }
-        if ($items->{$name}[0]) {
-          die "Multiple definitions for macro $name";
-        }
-        $item->{utf8} = 'yes';
-        $item->{name} = $name;
-        $items->{$name}[0] = $item;
-        # We have need for the utf8 flag.
-        $what->{''} = 1;
-      }
-      push @new_items, $item;
-    }
-    @items = @new_items;
-    # use Data::Dumper; print Dumper @items;
-  }
-  my $params = params ($what);
-
-  my ($body, @subs) = "static int\n$subname (pTHX_ const char *name";
-  $body .= ", STRLEN len" unless defined $namelen;
-  $body .= ", int utf8" if $params->{''};
-  $body .= ", IV *iv_return" if $params->{IV};
-  $body .= ", NV *nv_return" if $params->{NV};
-  $body .= ", const char **pv_return" if $params->{PV};
-  $body .= ", SV **sv_return" if $params->{SV};
-  $body .= ") {\n";
-
-  if (defined $namelen) {
-    # We are a child subroutine. Print the simple description
-    my $comment = 'When generated this function returned values for the list'
-      . ' of names given here.  However, subsequent manual editing may have'
-        . ' added or removed some.';
-    $body .= switch_clause (2, $comment, $namelen, $items, @items);
-  } else {
-    # We are the top level.
-    $body .= "  /* Initially switch on the length of the name.  */\n";
-    $body .= dogfood ($package, $subname, $default_type, $what, $indent,
-                      $breakout, @items);
-    $body .= "  switch (len) {\n";
-    # Need to group names of the same length
-    my @by_length;
-    foreach (@items) {
-      push @{$by_length[length $_->{name}]}, $_;
-    }
-    foreach my $i (0 .. $#by_length) {
-      next unless $by_length[$i];	# None of this length
-      $body .= "  case $i:\n";
-      if (@{$by_length[$i]} == 1) {
-        my $only_thing = $by_length[$i]->[0];
-        if ($only_thing->{utf8}) {
-          if ($only_thing->{utf8} eq 'yes') {
-            # With utf8 on flag item is passed in element 0
-            $body .= match_clause ([$only_thing]);
-          } else {
-            # With utf8 off flag item is passed in element 1
-            $body .= match_clause ([undef, $only_thing]);
-          }
-        } else {
-          $body .= match_clause ($only_thing);
-        }
-      } elsif (@{$by_length[$i]} < $breakout) {
-        $body .= switch_clause (4, '', $i, $items, @{$by_length[$i]});
-      } else {
-        # Only use the minimal set of parameters actually needed by the types
-        # of the names of this length.
-        my $what = {};
-        foreach (@{$by_length[$i]}) {
-          $what->{$_->{type}} = 1;
-          $what->{''} = 1 if $_->{utf8};
-        }
-        $params = params ($what);
-        push @subs, C_constant ($package, "${subname}_$i", $default_type, $what,
-                                $indent, [$i, $items], @{$by_length[$i]});
-        $body .= "    return ${subname}_$i (aTHX_ name";
-        $body .= ", utf8" if $params->{''};
-        $body .= ", iv_return" if $params->{IV};
-        $body .= ", nv_return" if $params->{NV};
-        $body .= ", pv_return" if $params->{PV};
-        $body .= ", sv_return" if $params->{SV};
-        $body .= ");\n";
-      }
-      $body .= "    break;\n";
-    }
-    $body .= "  }\n";
-  }
-  $body .= "  return PERL_constant_NOTFOUND;\n}\n";
-  return (@subs, $body);
+  ExtUtils::Constant::XS->C_constant({package => $package, subname => $subname,
+				      default_type => $default_type,
+				      types => $what, indent => $indent,
+				      breakout => $breakout}, @items);
 }
 
 =item XS_constant PACKAGE, TYPES, SUBNAME, C_SUBNAME
@@ -1124,7 +181,7 @@ sub XS_constant {
     # Convert line of the form IV,UV,NV to hash
     $what = {map {$_ => 1} split /,\s*/, ($what)};
   }
-  my $params = params ($what);
+  my $params = ExtUtils::Constant::XS->params ($what);
   my $type;
 
   my $xs = <<"EOT";
@@ -1341,9 +398,10 @@ EOT
 EOT
 
   $result =~ s/^/' 'x$indent/gem;
-  return dump_names ($args{DEFAULT_TYPE}, undef, $indent, undef,
-                           @{$args{NAMES}})
-          . $result;
+  return ExtUtils::Constant::XS->dump_names({default_type=>$args{DEFAULT_TYPE},
+					     indent=>$indent,},
+					    @{$args{NAMES}})
+    . $result;
 }
 
 =item WriteConstants ATTRIBUTE =E<gt> VALUE [, ...]
@@ -1428,8 +486,13 @@ sub WriteConstants {
   print $c_fh "\n";
 
   # indent is still undef. Until anyone implements indent style rules with it.
-  foreach (C_constant ($ARGS{NAME}, $ARGS{C_SUBNAME}, $ARGS{DEFAULT_TYPE},
-                       $types, undef, $ARGS{BREAKOUT_AT}, @{$ARGS{NAMES}})) {
+  foreach (ExtUtils::Constant::XS->C_constant({package => $ARGS{NAME},
+					       subname => $ARGS{C_SUBNAME},
+					       default_type =>
+					       $ARGS{DEFAULT_TYPE},
+					       types => $types,
+					       breakout => $ARGS{BREAKOUT_AT}},
+					       @{$ARGS{NAMES}})) {
     print $c_fh $_, "\n"; # C constant subs
   }
   print $xs_fh XS_constant ($ARGS{NAME}, $types, $ARGS{XS_SUBNAME},
@@ -1439,28 +502,6 @@ sub WriteConstants {
   close $xs_fh or warn "Error closing $ARGS{XS_FILE}: $!";
 }
 
-package ExtUtils::Constant::Aaargh56Hash;
-# A support module (hack) to provide sane Unicode hash keys on 5.6.x perl
-use strict;
-require Tie::Hash if $ExtUtils::Constant::is_perl56;
-use vars '@ISA';
-@ISA = 'Tie::StdHash';
-
-#my $a;
-# Storing the values as concatenated BER encoded numbers is actually going to
-# be terser than using UTF8 :-)
-# And the tests are slightly faster. Ops are bad, m'kay
-sub to_key {pack "w*", unpack "U*", ($_[0] . pack "U*")};
-sub from_key {defined $_[0] ? pack "U*", unpack 'w*', $_[0] : undef};
-
-sub STORE    { $_[0]->{to_key($_[1])} = $_[2] }
-sub FETCH    { $_[0]->{to_key($_[1])} }
-sub FIRSTKEY { my $a = scalar keys %{$_[0]}; from_key (each %{$_[0]}) }
-sub NEXTKEY  { from_key (each %{$_[0]}) }
-sub EXISTS   { exists $_[0]->{to_key($_[1])} }
-sub DELETE   { delete $_[0]->{to_key($_[1])} }
-
-#END {warn "$a accesses";}
 1;
 __END__
 
diff --git a/lib/ExtUtils/Constant/Base.pm b/lib/ExtUtils/Constant/Base.pm
new file mode 100644
index 0000000000..b98b030cf8
--- /dev/null
+++ b/lib/ExtUtils/Constant/Base.pm
@@ -0,0 +1,956 @@
+package ExtUtils::Constant::Base;
+
+use strict;
+use vars qw($VERSION $is_perl56);
+use Carp;
+use Text::Wrap;
+use ExtUtils::Constant::Utils qw(C_stringify perl_stringify);
+
+$VERSION = '0.01';
+
+$is_perl56 = ($] < 5.007 && $] > 5.005_50);
+
+
+=head1 NAME
+
+ExtUtils::Constant::Base - base class for ExtUtils::Constant objects
+
+=head1 SYNOPSIS
+
+    require ExtUtils::Constant::Base;
+    @ISA = 'ExtUtils::Constant::Base';
+
+=head1 DESCRIPTION
+
+ExtUtils::Constant::Base provides a base implementation of methods to
+generate C code to give fast constant value lookup by named string. Currently
+it's mostly used ExtUtils::Constant::XS, which generates the lookup code
+for the constant() subroutine found in many XS modules.
+
+=head1 USAGE
+
+ExtUtils::Constant::Base exports no subroutines. The following methods are
+available
+
+=over 4
+
+=cut
+
+sub valid_type {
+  # Default to assuming that you don't need different types of return data.
+  1;
+}
+sub default_type {
+  '';
+}
+
+=item header
+
+A method returning a scalar containing definitions needed, typically for a
+C header file.
+
+=cut
+
+sub header {
+  ''
+}
+
+# This might actually be a return statement. Note that you are responsible
+# for any space you might need before your value, as it lets to perform
+# "tricks" such as "return KEY_" and have strings appended.
+sub assignment_clause_for_type;
+# In which case this might be an empty string
+sub return_statement_for_type {undef};
+sub return_statement_for_notdef;
+sub return_statement_for_notfound;
+
+# "#if 1" is true to a C pre-processor
+sub macro_from_name {
+  1;
+}
+
+sub name_param {
+  'name';
+}
+
+# This is possibly buggy, in that it's not mandatory (below, in the main
+# C_constant parameters, but is expected to exist here, if it's needed)
+# Buggy because if you're definitely pure 8 bit only, and will never be
+# presented with your constants in utf8, the default form of C_constant can't
+# be told not to do the utf8 version.
+
+sub is_utf8_param {
+  'utf8';
+}
+
+sub memEQ {
+  "!memcmp";
+}
+
+=item memEQ_clause args_hashref
+
+A method to return a suitable C C<if> statement to check whether I<name>
+is equal to the C variable C<name>. If I<checked_at> is defined, then it
+is used to avoid C<memEQ> for short names, or to generate a comment to
+highlight the position of the character in the C<switch> statement.
+
+If i<checked_at> is a reference to a scalar, then instead it gives
+the characters pre-checked at the beginning, (and the number of chars by
+which the C variable name has been advanced. These need to be chopped from
+the front of I<name>).
+
+=cut
+
+sub memEQ_clause {
+#    if (memEQ(name, "thingy", 6)) {
+  # Which could actually be a character comparison or even ""
+  my ($self, $args) = @_;
+  my ($name, $checked_at, $indent) = @{$args}{qw(name checked_at indent)};
+  $indent = ' ' x ($indent || 4);
+  my $front_chop;
+  if (ref $checked_at) {
+    # regexp won't work on 5.6.1 without use utf8; in turn that won't work
+    # on 5.005_03.
+    substr ($name, 0, length $$checked_at,) = '';
+    $front_chop = C_stringify ($$checked_at);
+    undef $checked_at;
+  }
+  my $len = length $name;
+
+  if ($len < 2) {
+    return $indent . "{\n"
+	if (defined $checked_at and $checked_at == 0) or $len == 0;
+    # We didn't switch, drop through to the code for the 2 character string
+    $checked_at = 1;
+  }
+
+  my $name_param = $self->name_param;
+
+  if ($len < 3 and defined $checked_at) {
+    my $check;
+    if ($checked_at == 1) {
+      $check = 0;
+    } elsif ($checked_at == 0) {
+      $check = 1;
+    }
+    if (defined $check) {
+      my $char = C_stringify (substr $name, $check, 1);
+      # Placate 5.005 with a break in the string. I can't see a good way of
+      # getting it to not take [ as introducing an array lookup, even with
+      # ${name_param}[$check]
+      return $indent . "if ($name_param" . "[$check] == '$char') {\n";
+    }
+  }
+  if (($len == 2 and !defined $checked_at)
+     or ($len == 3 and defined ($checked_at) and $checked_at == 2)) {
+    my $char1 = C_stringify (substr $name, 0, 1);
+    my $char2 = C_stringify (substr $name, 1, 1);
+    return $indent .
+      "if ($name_param" . "[0] == '$char1' && $name_param" . "[1] == '$char2') {\n";
+  }
+  if (($len == 3 and defined ($checked_at) and $checked_at == 1)) {
+    my $char1 = C_stringify (substr $name, 0, 1);
+    my $char2 = C_stringify (substr $name, 2, 1);
+    return $indent .
+      "if ($name_param" . "[0] == '$char1' && $name_param" . "[2] == '$char2') {\n";
+  }
+
+  my $pointer = '^';
+  my $have_checked_last = defined ($checked_at) && $len == $checked_at + 1;
+  if ($have_checked_last) {
+    # Checked at the last character, so no need to memEQ it.
+    $pointer = C_stringify (chop $name);
+    $len--;
+  }
+
+  $name = C_stringify ($name);
+  my $memEQ = $self->memEQ();
+  my $body = $indent . "if ($memEQ($name_param, \"$name\", $len)) {\n";
+  # Put a little ^ under the letter we checked at
+  # Screws up for non printable and non-7 bit stuff, but that's too hard to
+  # get right.
+  if (defined $checked_at) {
+    $body .= $indent . "/*      " . (' ' x length $memEQ)
+      . (' ' x length $name_param)
+      . (' ' x $checked_at) . $pointer
+      . (' ' x ($len - $checked_at + length $len)) . "    */\n";
+  } elsif (defined $front_chop) {
+    $body .= $indent . "/*                $front_chop"
+      . (' ' x ($len + 1 + length $len)) . "    */\n";
+  }
+  return $body;
+}
+
+=item dump_names arg_hashref, ITEM...
+
+An internal function to generate the embedded perl code that will regenerate
+the constant subroutines.  I<default_type>, I<types> and I<ITEM>s are the
+same as for C_constant.  I<indent> is treated as number of spaces to indent
+by.  If C<declare_types> is true a C<$types> is always declared in the perl
+code generated, if defined and false never declared, and if undefined C<$types>
+is only declared if the values in I<types> as passed in cannot be inferred from
+I<default_types> and the I<ITEM>s.
+
+=cut
+
+sub dump_names {
+  my ($self, $args, @items) = @_;
+  my ($default_type, $what, $indent, $declare_types)
+    = @{$args}{qw(default_type what indent declare_types)};
+  $indent = ' ' x ($indent || 0);
+
+  my $result;
+  my (@simple, @complex, %used_types);
+  foreach (@items) {
+    my $type;
+    if (ref $_) {
+      $type = $_->{type} || $default_type;
+      if ($_->{utf8}) {
+        # For simplicity always skip the bytes case, and reconstitute this entry
+        # from its utf8 twin.
+        next if $_->{utf8} eq 'no';
+        # Copy the hashref, as we don't want to mess with the caller's hashref.
+        $_ = {%$_};
+        unless ($is_perl56) {
+          utf8::decode ($_->{name});
+        } else {
+          $_->{name} = pack 'U*', unpack 'U0U*', $_->{name};
+        }
+        delete $_->{utf8};
+      }
+    } else {
+      $_ = {name=>$_};
+      $type = $default_type;
+    }
+    $used_types{$type}++;
+    if ($type eq $default_type
+        # grr 5.6.1
+        and length $_->{name}
+        and length $_->{name} == ($_->{name} =~ tr/A-Za-z0-9_//)
+        and !defined ($_->{macro}) and !defined ($_->{value})
+        and !defined ($_->{default}) and !defined ($_->{pre})
+        and !defined ($_->{post}) and !defined ($_->{def_pre})
+        and !defined ($_->{def_post})) {
+      # It's the default type, and the name consists only of A-Za-z0-9_
+      push @simple, $_->{name};
+    } else {
+      push @complex, $_;
+    }
+  }
+
+  if (!defined $declare_types) {
+    # Do they pass in any types we weren't already using?
+    foreach (keys %$what) {
+      next if $used_types{$_};
+      $declare_types++; # Found one in $what that wasn't used.
+      last; # And one is enough to terminate this loop
+    }
+  }
+  if ($declare_types) {
+    $result = $indent . 'my $types = {map {($_, 1)} qw('
+      . join (" ", sort keys %$what) . ")};\n";
+  }
+  local $Text::Wrap::huge = 'overflow';
+  local $Text::Wrap::columns = 80;
+  $result .= wrap ($indent . "my \@names = (qw(",
+		   $indent . "               ", join (" ", sort @simple) . ")");
+  if (@complex) {
+    foreach my $item (sort {$a->{name} cmp $b->{name}} @complex) {
+      my $name = perl_stringify $item->{name};
+      my $line = ",\n$indent            {name=>\"$name\"";
+      $line .= ", type=>\"$item->{type}\"" if defined $item->{type};
+      foreach my $thing (qw (macro value default pre post def_pre def_post)) {
+        my $value = $item->{$thing};
+        if (defined $value) {
+          if (ref $value) {
+            $line .= ", $thing=>[\""
+              . join ('", "', map {perl_stringify $_} @$value) . '"]';
+          } else {
+            $line .= ", $thing=>\"" . perl_stringify($value) . "\"";
+          }
+        }
+      }
+      $line .= "}";
+      # Ensure that the enclosing C comment doesn't end
+      # by turning */  into *" . "/
+      $line =~ s!\*\/!\*" . "/!gs;
+      # gcc -Wall doesn't like finding /* inside a comment
+      $line =~ s!\/\*!/" . "\*!gs;
+      $result .= $line;
+    }
+  }
+  $result .= ");\n";
+
+  $result;
+}
+
+=item assign arg_hashref, VALUE...
+
+A method to return a suitable assignment clause. If I<type> is aggregate
+(eg I<PVN> expects both pointer and length) then there should be multiple
+I<VALUE>s for the components. I<pre> and I<post> if defined give snippets
+of C code to proceed and follow the assignment. I<pre> will be at the start
+of a block, so variables may be defined in it.
+
+=cut
+# Hmm. value undef to to NOTDEF? value () to do NOTFOUND?
+
+sub assign {
+  my $self = shift;
+  my $args = shift;
+  my ($indent, $type, $pre, $post) = @{$args}{qw(indent type pre post)};
+  $post ||= '';
+  my $clause;
+  my $close;
+  if ($pre) {
+    chomp $pre;
+    $close = "$indent}\n";
+    $clause = $indent . "{\n";
+    $indent .= "  ";
+    $clause .= "$indent$pre";
+    $clause .= ";" unless $pre =~ /;$/;
+    $clause .= "\n";
+  }
+  confess "undef \$type" unless defined $type;
+  confess "Can't generate code for type $type"
+    unless $self->valid_type($type);
+
+  $clause .= join '', map {"$indent$_\n"}
+    $self->assignment_clause_for_type($type, @_);
+  chomp $post;
+  if (length $post) {
+    $clause .= "$post";
+    $clause .= ";" unless $post =~ /;$/;
+    $clause .= "\n";
+  }
+  my $return = $self->return_statement_for_type($type);
+  $clause .= "$indent$return\n" if defined $return;
+  $clause .= $close if $close;
+  return $clause;
+}
+
+=item return_clause arg_hashref, ITEM
+
+A method to return a suitable C<#ifdef> clause. I<ITEM> is a hashref
+(as passed to C<C_constant> and C<match_clause>. I<indent> is the number
+of spaces to indent, defaulting to 6.
+
+=cut
+
+sub return_clause {
+
+##ifdef thingy
+#      *iv_return = thingy;
+#      return PERL_constant_ISIV;
+##else
+#      return PERL_constant_NOTDEF;
+##endif
+  my ($self, $args, $item) = @_;
+  my $indent = $args->{indent};
+
+  my ($name, $value, $macro, $default, $pre, $post, $def_pre, $def_post, $type)
+    = @$item{qw (name value macro default pre post def_pre def_post type)};
+  $value = $name unless defined $value;
+  $macro = $self->macro_from_name($item) unless defined $macro;
+  # "#if 1" is true to a C pre-processor
+  $macro = 1 if !defined $macro or $macro eq '';
+  $indent = ' ' x ($indent || 6);
+  unless (defined $type) {
+    # use Data::Dumper; print STDERR Dumper ($item);
+    confess "undef \$type";
+  }
+
+  my $clause;
+
+  ##ifdef thingy
+  if (ref $macro) {
+    $clause = $macro->[0];
+  } elsif ($macro ne "1") {
+    $clause = "#ifdef $macro\n";
+  }
+
+  #      *iv_return = thingy;
+  #      return PERL_constant_ISIV;
+  $clause
+    .= $self->assign ({indent=>$indent, type=>$type, pre=>$pre, post=>$post},
+		      ref $value ? @$value : $value);
+
+  if (ref $macro or $macro ne "1") {
+    ##else
+    $clause .= "#else\n";
+
+    #      return PERL_constant_NOTDEF;
+    if (!defined $default) {
+      my $notdef = $self->return_statement_for_notdef();
+      $clause .= "$indent$notdef\n" if defined $notdef;
+    } else {
+      my @default = ref $default ? @$default : $default;
+      $type = shift @default;
+      $clause .= $self->assign ({indent=>$indent, type=>$type, pre=>$pre,
+				 post=>$post}, @default);
+    }
+
+    ##endif
+    if (ref $macro) {
+      $clause .= $macro->[1];
+    } else {
+      $clause .= "#endif\n";
+    }
+  }
+  return $clause;
+}
+
+sub match_clause {
+  # $offset defined if we have checked an offset.
+  my ($self, $args, $item) = @_;
+  my ($offset, $indent) = @{$args}{qw(checked_at indent)};
+  $indent = ' ' x ($indent || 4);
+  my $body = '';
+  my ($no, $yes, $either, $name, $inner_indent);
+  if (ref $item eq 'ARRAY') {
+    ($yes, $no) = @$item;
+    $either = $yes || $no;
+    confess "$item is $either expecting hashref in [0] || [1]"
+      unless ref $either eq 'HASH';
+    $name = $either->{name};
+  } else {
+    confess "$item->{name} has utf8 flag '$item->{utf8}', should be false"
+      if $item->{utf8};
+    $name = $item->{name};
+    $inner_indent = $indent;
+  }
+
+  $body .= $self->memEQ_clause ({name => $name, checked_at => $offset,
+				 indent => length $indent});
+  # If we've been presented with an arrayref for $item, then the user string
+  # contains in the range 128-255, and we need to check whether it was utf8
+  # (or not).
+  # In the worst case we have two named constants, where one's name happens
+  # encoded in UTF8 happens to be the same byte sequence as the second's
+  # encoded in (say) ISO-8859-1.
+  # In this case, $yes and $no both have item hashrefs.
+  if ($yes) {
+    $body .= $indent . "  if (" . $self->is_utf8_param . ") {\n";
+  } elsif ($no) {
+    $body .= $indent . "  if (!" . $self->is_utf8_param . ") {\n";
+  }
+  if ($either) {
+    $body .= $self->return_clause ({indent=>4 + length $indent}, $either);
+    if ($yes and $no) {
+      $body .= $indent . "  } else {\n";
+      $body .= $self->return_clause ({indent=>4 + length $indent}, $no);
+    }
+    $body .= $indent . "  }\n";
+  } else {
+    $body .= $self->return_clause ({indent=>2 + length $indent}, $item);
+  }
+  $body .= $indent . "}\n";
+}
+
+
+=item switch_clause arg_hashref, NAMELEN, ITEMHASH, ITEM...
+
+An internal method to generate a suitable C<switch> clause, called by
+C<C_constant> I<ITEM>s are in the hash ref format as given in the description
+of C<C_constant>, and must all have the names of the same length, given by
+I<NAMELEN>.  I<ITEMHASH> is a reference to a hash, keyed by name, values being
+the hashrefs in the I<ITEM> list.  (No parameters are modified, and there can
+be keys in the I<ITEMHASH> that are not in the list of I<ITEM>s without
+causing problems - the hash is passed in to save generating it afresh for
+each call).
+
+=cut
+
+sub switch_clause {
+  my ($self, $args, $namelen, $items, @items) = @_;
+  my ($indent, $comment) = @{$args}{qw(indent comment)};
+  $indent = ' ' x ($indent || 2);
+
+  local $Text::Wrap::huge = 'overflow';
+  local $Text::Wrap::columns = 80;
+
+  my @names = sort map {$_->{name}} @items;
+  my $leader = $indent . '/* ';
+  my $follower = ' ' x length $leader;
+  my $body = $indent . "/* Names all of length $namelen.  */\n";
+  if (defined $comment) {
+    $body = wrap ($leader, $follower, $comment) . "\n";
+    $leader = $follower;
+  }
+  my @safe_names = @names;
+  foreach (@safe_names) {
+    confess sprintf "Name '$_' is length %d, not $namelen", length
+      unless length == $namelen;
+    # Argh. 5.6.1
+    # next unless tr/A-Za-z0-9_//c;
+    next if tr/A-Za-z0-9_// == length;
+    $_ = '"' . perl_stringify ($_) . '"';
+    # Ensure that the enclosing C comment doesn't end
+    # by turning */  into *" . "/
+    s!\*\/!\*"."/!gs;
+    # gcc -Wall doesn't like finding /* inside a comment
+    s!\/\*!/"."\*!gs;
+  }
+  $body .= wrap ($leader, $follower, join (" ", @safe_names) . " */") . "\n";
+  # Figure out what to switch on.
+  # (RMS, Spread of jump table, Position, Hashref)
+  my @best = (1e38, ~0);
+  # Prefer the last character over the others. (As it lets us shorten the
+  # memEQ clause at no cost).
+  foreach my $i ($namelen - 1, 0 .. ($namelen - 2)) {
+    my ($min, $max) = (~0, 0);
+    my %spread;
+    if ($is_perl56) {
+      # Need proper Unicode preserving hash keys for bytes in range 128-255
+      # here too, for some reason. grr 5.6.1 yet again.
+      tie %spread, 'ExtUtils::Constant::Aaargh56Hash';
+    }
+    foreach (@names) {
+      my $char = substr $_, $i, 1;
+      my $ord = ord $char;
+      confess "char $ord is out of range" if $ord > 255;
+      $max = $ord if $ord > $max;
+      $min = $ord if $ord < $min;
+      push @{$spread{$char}}, $_;
+      # warn "$_ $char";
+    }
+    # I'm going to pick the character to split on that minimises the root
+    # mean square of the number of names in each case. Normally this should
+    # be the one with the most keys, but it may pick a 7 where the 8 has
+    # one long linear search. I'm not sure if RMS or just sum of squares is
+    # actually better.
+    # $max and $min are for the tie-breaker if the root mean squares match.
+    # Assuming that the compiler may be building a jump table for the
+    # switch() then try to minimise the size of that jump table.
+    # Finally use < not <= so that if it still ties the earliest part of
+    # the string wins. Because if that passes but the memEQ fails, it may
+    # only need the start of the string to bin the choice.
+    # I think. But I'm micro-optimising. :-)
+    # OK. Trump that. Now favour the last character of the string, before the
+    # rest.
+    my $ss;
+    $ss += @$_ * @$_ foreach values %spread;
+    my $rms = sqrt ($ss / keys %spread);
+    if ($rms < $best[0] || ($rms == $best[0] && ($max - $min) < $best[1])) {
+      @best = ($rms, $max - $min, $i, \%spread);
+    }
+  }
+  confess "Internal error. Failed to pick a switch point for @names"
+    unless defined $best[2];
+  # use Data::Dumper; print Dumper (@best);
+  my ($offset, $best) = @best[2,3];
+  $body .= $indent . "/* Offset $offset gives the best switch position.  */\n";
+
+  my $do_front_chop = $offset == 0 && $namelen > 2;
+  if ($do_front_chop) {
+    $body .= $indent . "switch (*" . $self->name_param() . "++) {\n";
+  } else {
+    $body .= $indent . "switch (" . $self->name_param() . "[$offset]) {\n";
+  }
+  foreach my $char (sort keys %$best) {
+    confess sprintf "'$char' is %d bytes long, not 1", length $char
+      if length ($char) != 1;
+    confess sprintf "char %#X is out of range", ord $char if ord ($char) > 255;
+    $body .= $indent . "case '" . C_stringify ($char) . "':\n";
+    foreach my $name (sort @{$best->{$char}}) {
+      my $thisone = $items->{$name};
+      # warn "You are here";
+      if ($do_front_chop) {
+        $body .= $self->match_clause ({indent => 2 + length $indent,
+				       checked_at => \$char}, $thisone);
+      } else {
+        $body .= $self->match_clause ({indent => 2 + length $indent,
+				       checked_at => $offset}, $thisone);
+      }
+    }
+    $body .= $indent . "  break;\n";
+  }
+  $body .= $indent . "}\n";
+  return $body;
+}
+
+sub C_constant_return_type {
+  "static int";
+}
+
+sub C_constant_prefix_param {
+  '';
+}
+
+sub C_constant_prefix_param_defintion {
+  '';
+}
+
+sub C_constant_name_param_definition {
+  "const char *" . $_[0]->name_param;
+}
+
+sub C_constant_namelen_param {
+  'len';
+}
+
+sub C_constant_namelen_param_definition {
+  'size_t ' . $_[0] -> C_constant_namelen_param;
+}
+
+sub C_constant_param {
+  '';
+}
+
+sub C_constant_param_defintion {
+  '';
+}
+
+=item params WHAT
+
+An "internal" method, subject to change, currently called to allow an
+overriding class to cache information that will then be passed into all
+the C<*param*> calls. (Yes, having to read the source to make sense of this is
+considered a known bug). I<WHAT> is be a hashref of types the constant
+function will return. In ExtUtils::Constant::XS this method is used to
+returns a hashref keyed IV NV PV SV to show which combination of pointers will
+be needed in the C argument list generated by C_constant_param_definition
+and C_constant_param
+
+=cut
+
+sub params {
+  '';
+}
+
+
+=item dogfood arg_hashref, ITEM...
+
+An internal function to generate the embedded perl code that will regenerate
+the constant subroutines.  Parameters are the same as for C_constant.
+
+Currently the base class does nothing and returns an empty string.
+
+=cut
+
+sub dogfood {
+  ''
+}
+
+=item C_constant arg_hashref, ITEM...
+
+A function that returns a B<list> of C subroutine definitions that return
+the value and type of constants when passed the name by the XS wrapper.
+I<ITEM...> gives a list of constant names. Each can either be a string,
+which is taken as a C macro name, or a reference to a hash with the following
+keys
+
+=over 8
+
+=item name
+
+The name of the constant, as seen by the perl code.
+
+=item type
+
+The type of the constant (I<IV>, I<NV> etc)
+
+=item value
+
+A C expression for the value of the constant, or a list of C expressions if
+the type is aggregate. This defaults to the I<name> if not given.
+
+=item macro
+
+The C pre-processor macro to use in the C<#ifdef>. This defaults to the
+I<name>, and is mainly used if I<value> is an C<enum>. If a reference an
+array is passed then the first element is used in place of the C<#ifdef>
+line, and the second element in place of the C<#endif>. This allows
+pre-processor constructions such as
+
+    #if defined (foo)
+    #if !defined (bar)
+    ...
+    #endif
+    #endif
+
+to be used to determine if a constant is to be defined.
+
+A "macro" 1 signals that the constant is always defined, so the C<#if>/C<#endif>
+test is omitted.
+
+=item default
+
+Default value to use (instead of C<croak>ing with "your vendor has not
+defined...") to return if the macro isn't defined. Specify a reference to
+an array with type followed by value(s).
+
+=item pre
+
+C code to use before the assignment of the value of the constant. This allows
+you to use temporary variables to extract a value from part of a C<struct>
+and return this as I<value>. This C code is places at the start of a block,
+so you can declare variables in it.
+
+=item post
+
+C code to place between the assignment of value (to a temporary) and the
+return from the function. This allows you to clear up anything in I<pre>.
+Rarely needed.
+
+=item def_pre
+
+=item def_post
+
+Equivalents of I<pre> and I<post> for the default value.
+
+=item utf8
+
+Generated internally. Is zero or undefined if name is 7 bit ASCII,
+"no" if the name is 8 bit (and so should only match if SvUTF8() is false),
+"yes" if the name is utf8 encoded.
+
+The internals automatically clone any name with characters 128-255 but none
+256+ (ie one that could be either in bytes or utf8) into a second entry
+which is utf8 encoded.
+
+=back
+
+In the argument hashref, I<package> is the name of the package, and is only
+used in comments inside the generated C code. I<subname> defaults to
+C<constant> if undefined.
+
+I<default_type> is the type returned by C<ITEM>s that don't specify their
+type. It defaults to the value of C<default_type()>. I<types> should be given
+either as a comma separated list of types that the C subroutine I<subname>
+will generate or as a reference to a hash. I<default_type> will be added to
+the list if not present, as will any types given in the list of I<ITEM>s. The
+resultant list should be the same list of types that C<XS_constant> is
+given. [Otherwise C<XS_constant> and C<C_constant> may differ in the number of
+parameters to the constant function. I<indent> is currently unused and
+ignored. In future it may be used to pass in information used to change the C
+indentation style used.]  The best way to maintain consistency is to pass in a
+hash reference and let this function update it.
+
+I<breakout> governs when child functions of I<subname> are generated.  If there
+are I<breakout> or more I<ITEM>s with the same length of name, then the code
+to switch between them is placed into a function named I<subname>_I<len>, for
+example C<constant_5> for names 5 characters long.  The default I<breakout> is
+3.  A single C<ITEM> is always inlined.
+
+=cut
+
+# The parameter now BREAKOUT was previously documented as:
+#
+# I<NAMELEN> if defined signals that all the I<name>s of the I<ITEM>s are of
+# this length, and that the constant name passed in by perl is checked and
+# also of this length. It is used during recursion, and should be C<undef>
+# unless the caller has checked all the lengths during code generation, and
+# the generated subroutine is only to be called with a name of this length.
+#
+# As you can see it now performs this function during recursion by being a
+# scalar reference.
+
+sub C_constant {
+  my ($self, $args, @items) = @_;
+  my ($package, $subname, $default_type, $what, $indent, $breakout) =
+    @{$args}{qw(package subname default_type types indent breakout)};
+  $package ||= 'Foo';
+  $subname ||= 'constant';
+  # I'm not using this. But a hashref could be used for full formatting without
+  # breaking this API
+  # $indent ||= 0;
+
+  my ($namelen, $items);
+  if (ref $breakout) {
+    # We are called recursively. We trust @items to be normalised, $what to
+    # be a hashref, and pinch %$items from our parent to save recalculation.
+    ($namelen, $items) = @$breakout;
+  } else {
+    if ($is_perl56) {
+      # Need proper Unicode preserving hash keys.
+      require ExtUtils::Constant::Aaargh56Hash;
+      $items = {};
+      tie %$items, 'ExtUtils::Constant::Aaargh56Hash';
+    }
+    $breakout ||= 3;
+    $default_type ||= $self->default_type();
+    if (!ref $what) {
+      # Convert line of the form IV,UV,NV to hash
+      $what = {map {$_ => 1} split /,\s*/, ($what || '')};
+      # Figure out what types we're dealing with, and assign all unknowns to the
+      # default type
+    }
+    my @new_items;
+    foreach my $orig (@items) {
+      my ($name, $item);
+      if (ref $orig) {
+        # Make a copy which is a normalised version of the ref passed in.
+        $name = $orig->{name};
+        my ($type, $macro, $value) = @$orig{qw (type macro value)};
+        $type ||= $default_type;
+        $what->{$type} = 1;
+        $item = {name=>$name, type=>$type};
+
+        undef $macro if defined $macro and $macro eq $name;
+        $item->{macro} = $macro if defined $macro;
+        undef $value if defined $value and $value eq $name;
+        $item->{value} = $value if defined $value;
+        foreach my $key (qw(default pre post def_pre def_post)) {
+          my $value = $orig->{$key};
+          $item->{$key} = $value if defined $value;
+          # warn "$key $value";
+        }
+      } else {
+        $name = $orig;
+        $item = {name=>$name, type=>$default_type};
+        $what->{$default_type} = 1;
+      }
+      warn +(ref ($self) || $self)
+	. "doesn't know how to handle values of type $_ used in macro $name"
+	  unless $self->valid_type ($item->{type});
+      # tr///c is broken on 5.6.1 for utf8, so my original tr/\0-\177//c
+      # doesn't work. Upgrade to 5.8
+      # if ($name !~ tr/\0-\177//c || $] < 5.005_50) {
+      if ($name =~ tr/\0-\177// == length $name || $] < 5.005_50) {
+        # No characters outside 7 bit ASCII.
+        if (exists $items->{$name}) {
+          die "Multiple definitions for macro $name";
+        }
+        $items->{$name} = $item;
+      } else {
+        # No characters outside 8 bit. This is hardest.
+        if (exists $items->{$name} and ref $items->{$name} ne 'ARRAY') {
+          confess "Unexpected ASCII definition for macro $name";
+        }
+        # Again, 5.6.1 tr broken, so s/5\.6.*/5\.8\.0/;
+        # if ($name !~ tr/\0-\377//c) {
+        if ($name =~ tr/\0-\377// == length $name) {
+#          if ($] < 5.007) {
+#            $name = pack "C*", unpack "U*", $name;
+#          }
+          $item->{utf8} = 'no';
+          $items->{$name}[1] = $item;
+          push @new_items, $item;
+          # Copy item, to create the utf8 variant.
+          $item = {%$item};
+        }
+        # Encode the name as utf8 bytes.
+        unless ($is_perl56) {
+          utf8::encode($name);
+        } else {
+#          warn "Was >$name< " . length ${name};
+          $name = pack 'C*', unpack 'C*', $name . pack 'U*';
+#          warn "Now '${name}' " . length ${name};
+        }
+        if ($items->{$name}[0]) {
+          die "Multiple definitions for macro $name";
+        }
+        $item->{utf8} = 'yes';
+        $item->{name} = $name;
+        $items->{$name}[0] = $item;
+        # We have need for the utf8 flag.
+        $what->{''} = 1;
+      }
+      push @new_items, $item;
+    }
+    @items = @new_items;
+    # use Data::Dumper; print Dumper @items;
+  }
+  my $params = $self->params ($what);
+
+  # Probably "static int"
+  my ($body, @subs);
+  $body = $self->C_constant_return_type($params) . "\n$subname ("
+    # Eg "pTHX_ "
+    . $self->C_constant_prefix_param_defintion($params)
+      # Probably "const char *name"
+      . $self->C_constant_name_param_definition($params);
+  # Something like ", STRLEN len"
+  $body .= ", " . $self->C_constant_namelen_param_definition($params)
+    unless defined $namelen;
+  $body .= $self->C_constant_param_defintion($params);
+  $body .= ") {\n";
+
+  if (defined $namelen) {
+    # We are a child subroutine. Print the simple description
+    my $comment = 'When generated this function returned values for the list'
+      . ' of names given here.  However, subsequent manual editing may have'
+        . ' added or removed some.';
+    $body .= $self->switch_clause ({indent=>2, comment=>$comment},
+				   $namelen, $items, @items);
+  } else {
+    # We are the top level.
+    $body .= "  /* Initially switch on the length of the name.  */\n";
+    $body .= $self->dogfood ({package => $package, subname => $subname,
+			      default_type => $default_type, what => $what,
+			      indent => $indent, breakout => $breakout},
+			     @items);
+    $body .= '  switch ('.$self->C_constant_namelen_param().") {\n";
+    # Need to group names of the same length
+    my @by_length;
+    foreach (@items) {
+      push @{$by_length[length $_->{name}]}, $_;
+    }
+    foreach my $i (0 .. $#by_length) {
+      next unless $by_length[$i];	# None of this length
+      $body .= "  case $i:\n";
+      if (@{$by_length[$i]} == 1) {
+        my $only_thing = $by_length[$i]->[0];
+        if ($only_thing->{utf8}) {
+          if ($only_thing->{utf8} eq 'yes') {
+            # With utf8 on flag item is passed in element 0
+            $body .= $self->match_clause (undef, [$only_thing]);
+          } else {
+            # With utf8 off flag item is passed in element 1
+            $body .= $self->match_clause (undef, [undef, $only_thing]);
+          }
+        } else {
+          $body .= $self->match_clause (undef, $only_thing);
+        }
+      } elsif (@{$by_length[$i]} < $breakout) {
+        $body .= $self->switch_clause ({indent=>4},
+				       $i, $items, @{$by_length[$i]});
+      } else {
+        # Only use the minimal set of parameters actually needed by the types
+        # of the names of this length.
+        my $what = {};
+        foreach (@{$by_length[$i]}) {
+          $what->{$_->{type}} = 1;
+          $what->{''} = 1 if $_->{utf8};
+        }
+        $params = $self->params ($what);
+        push @subs, $self->C_constant ({package=>$package,
+					subname=>"${subname}_$i",
+					default_type => $default_type,
+					types => $what, indent => $indent,
+					breakout => [$i, $items]},
+				       @{$by_length[$i]});
+        $body .= "    return ${subname}_$i ("
+	  # Eg "aTHX_ "
+	  . $self->C_constant_prefix_param($params)
+	    # Probably "name"
+	    . $self->name_param($params);
+	$body .= $self->C_constant_param($params);
+        $body .= ");\n";
+      }
+      $body .= "    break;\n";
+    }
+    $body .= "  }\n";
+  }
+  my $notfound = $self->return_statement_for_notfound();
+  $body .= "  $notfound\n" if $notfound;
+  $body .= "}\n";
+  return (@subs, $body);
+}
+
+1;
+__END__
+
+=back
+
+=head1 BUGS
+
+Not everything is documented yet.
+
+Probably others.
+
+=head1 AUTHOR
+
+Nicholas Clark <nick@ccl4.org> based on the code in C<h2xs> by Larry Wall and
+others
diff --git a/lib/ExtUtils/Constant/Utils.pm b/lib/ExtUtils/Constant/Utils.pm
new file mode 100644
index 0000000000..3ef2228c87
--- /dev/null
+++ b/lib/ExtUtils/Constant/Utils.pm
@@ -0,0 +1,123 @@
+package ExtUtils::Constant::Utils;
+
+use strict;
+use vars qw($VERSION @EXPORT_OK @ISA $is_perl56);
+use Carp;
+
+@ISA = 'Exporter';
+@EXPORT_OK = qw(C_stringify perl_stringify);
+$VERSION = '0.01';
+
+$is_perl56 = ($] < 5.007 && $] > 5.005_50);
+
+=head1 NAME
+
+ExtUtils::Constant::Utils - helper functions for ExtUtils::Constant
+
+=head1 SYNOPSIS
+
+    use ExtUtils::Constant::Utils qw (C_stringify);
+    $C_code = C_stringify $stuff;
+
+=head1 DESCRIPTION
+
+ExtUtils::Constant::Utils packages up utility subroutines used by
+ExtUtils::Constant, ExtUtils::Constant::Base and derived classes. All its
+functions are explicitly exportable.
+
+=head1 USAGE
+
+=over 4
+
+=item C_stringify NAME
+
+A function which returns a 7 bit ASCII correctly \ escaped version of the
+string passed suitable for C's "" or ''. It will die if passed Unicode
+characters.
+
+=cut
+
+# Hopefully make a happy C identifier.
+sub C_stringify {
+  local $_ = shift;
+  return unless defined $_;
+  # grr 5.6.1
+  confess "Wide character in '$_' intended as a C identifier"
+    if tr/\0-\377// != length;
+  # grr 5.6.1 moreso because its regexps will break on data that happens to
+  # be utf8, which includes my 8 bit test cases.
+  $_ = pack 'C*', unpack 'U*', $_ . pack 'U*' if $is_perl56;
+  s/\\/\\\\/g;
+  s/([\"\'])/\\$1/g;	# Grr. fix perl mode.
+  s/\n/\\n/g;		# Ensure newlines don't end up in octal
+  s/\r/\\r/g;
+  s/\t/\\t/g;
+  s/\f/\\f/g;
+  s/\a/\\a/g;
+  s/([^\0-\177])/sprintf "\\%03o", ord $1/ge;
+  unless ($] < 5.006) {
+    # This will elicit a warning on 5.005_03 about [: :] being reserved unless
+    # I cheat
+    my $cheat = '([[:^print:]])';
+    s/$cheat/sprintf "\\%03o", ord $1/ge;
+  } else {
+    require POSIX;
+    s/([^A-Za-z0-9_])/POSIX::isprint($1) ? $1 : sprintf "\\%03o", ord $1/ge;
+  }
+  $_;
+}
+
+=item perl_stringify NAME
+
+A function which returns a 7 bit ASCII correctly \ escaped version of the
+string passed suitable for a perl "" string.
+
+=cut
+
+# Hopefully make a happy perl identifier.
+sub perl_stringify {
+  local $_ = shift;
+  return unless defined $_;
+  s/\\/\\\\/g;
+  s/([\"\'])/\\$1/g;	# Grr. fix perl mode.
+  s/\n/\\n/g;		# Ensure newlines don't end up in octal
+  s/\r/\\r/g;
+  s/\t/\\t/g;
+  s/\f/\\f/g;
+  s/\a/\\a/g;
+  unless ($] < 5.006) {
+    if ($] > 5.007) {
+      s/([^\0-\177])/sprintf "\\x{%X}", ord $1/ge;
+    } else {
+      # Grr 5.6.1. And I don't think I can use utf8; to force the regexp
+      # because 5.005_03 will fail.
+      # This is grim, but I also can't split on //
+      my $copy;
+      foreach my $index (0 .. length ($_) - 1) {
+        my $char = substr ($_, $index, 1);
+        $copy .= ($char le "\177") ? $char : sprintf "\\x{%X}", ord $char;
+      }
+      $_ = $copy;
+    }
+    # This will elicit a warning on 5.005_03 about [: :] being reserved unless
+    # I cheat
+    my $cheat = '([[:^print:]])';
+    s/$cheat/sprintf "\\%03o", ord $1/ge;
+  } else {
+    # Turns out "\x{}" notation only arrived with 5.6
+    s/([^\0-\177])/sprintf "\\x%02X", ord $1/ge;
+    require POSIX;
+    s/([^A-Za-z0-9_])/POSIX::isprint($1) ? $1 : sprintf "\\%03o", ord $1/ge;
+  }
+  $_;
+}
+
+1;
+__END__
+
+=back
+
+=head1 AUTHOR
+
+Nicholas Clark <nick@ccl4.org> based on the code in C<h2xs> by Larry Wall and
+others
diff --git a/lib/ExtUtils/Constant/XS.pm b/lib/ExtUtils/Constant/XS.pm
new file mode 100644
index 0000000000..2faab85022
--- /dev/null
+++ b/lib/ExtUtils/Constant/XS.pm
@@ -0,0 +1,252 @@
+package ExtUtils::Constant::XS;
+
+use strict;
+use vars qw($VERSION %XS_Constant %XS_TypeSet @ISA @EXPORT_OK $is_perl56);
+use Carp;
+use ExtUtils::Constant::Utils 'perl_stringify';
+require ExtUtils::Constant::Base;
+
+
+@ISA = qw(ExtUtils::Constant::Base Exporter);
+@EXPORT_OK = qw(%XS_Constant %XS_TypeSet);
+
+$VERSION = '0.01';
+
+$is_perl56 = ($] < 5.007 && $] > 5.005_50);
+
+=head1 NAME
+
+ExtUtils::Constant::Base - base class for ExtUtils::Constant objects
+
+=head1 SYNOPSIS
+
+    require ExtUtils::Constant::XS;
+
+=head1 DESCRIPTION
+
+ExtUtils::Constant::XS overrides ExtUtils::Constant::Base to generate C
+code for XS modules' constants.
+
+=head1 BUGS
+
+Nothing is documented.
+
+Probably others.
+
+=head1 AUTHOR
+
+Nicholas Clark <nick@ccl4.org> based on the code in C<h2xs> by Larry Wall and
+others
+
+=cut
+
+# '' is used as a flag to indicate non-ascii macro names, and hence the need
+# to pass in the utf8 on/off flag.
+%XS_Constant = (
+		''    => '',
+		IV    => 'PUSHi(iv)',
+		UV    => 'PUSHu((UV)iv)',
+		NV    => 'PUSHn(nv)',
+		PV    => 'PUSHp(pv, strlen(pv))',
+		PVN   => 'PUSHp(pv, iv)',
+		SV    => 'PUSHs(sv)',
+		YES   => 'PUSHs(&PL_sv_yes)',
+		NO    => 'PUSHs(&PL_sv_no)',
+		UNDEF => '',	# implicit undef
+);
+
+%XS_TypeSet = (
+		IV    => '*iv_return = ',
+		UV    => '*iv_return = (IV)',
+		NV    => '*nv_return = ',
+		PV    => '*pv_return = ',
+		PVN   => ['*pv_return = ', '*iv_return = (IV)'],
+		SV    => '*sv_return = ',
+		YES   => undef,
+		NO    => undef,
+		UNDEF => undef,
+);
+
+sub header {
+  my $start = 1;
+  my @lines;
+  push @lines, "#define PERL_constant_NOTFOUND\t$start\n"; $start++;
+  push @lines, "#define PERL_constant_NOTDEF\t$start\n"; $start++;
+  foreach (sort keys %XS_Constant) {
+    next if $_ eq '';
+    push @lines, "#define PERL_constant_IS$_\t$start\n"; $start++;
+  }
+  push @lines, << 'EOT';
+
+#ifndef NVTYPE
+typedef double NV; /* 5.6 and later define NVTYPE, and typedef NV to it.  */
+#endif
+#ifndef aTHX_
+#define aTHX_ /* 5.6 or later define this for threading support.  */
+#endif
+#ifndef pTHX_
+#define pTHX_ /* 5.6 or later define this for threading support.  */
+#endif
+EOT
+
+  return join '', @lines;
+}
+
+sub valid_type {
+  my ($self, $type) = @_;
+  return exists $XS_TypeSet{$type};
+}
+
+# This might actually be a return statement
+sub assignment_clause_for_type {
+  my $self = shift;
+  # In the future may pass in an options hash
+  my $type = shift;
+  $type = $type->{type} if ref $type;
+  my $typeset = $XS_TypeSet{$type};
+  if (ref $typeset) {
+    die "Type $type is aggregate, but only single value given"
+      if @_ == 1;
+    return map {"$typeset->[$_]$_[$_];"} 0 .. $#$typeset;
+  } elsif (defined $typeset) {
+    confess "Aggregate value given for type $type"
+      if @_ > 1;
+    return "$typeset$_[0];";
+  }
+  return ();
+}
+
+sub return_statement_for_type {
+  my ($self, $type) = @_;
+  $type = $type->{type} if ref $type;
+  "return PERL_constant_IS$type;";
+}
+
+sub return_statement_for_notdef {
+  # my ($self) = @_;
+  "return PERL_constant_NOTDEF;";
+}
+
+sub return_statement_for_notfound {
+  # my ($self) = @_;
+  "return PERL_constant_NOTFOUND;";
+}
+
+sub default_type {
+  'IV';
+}
+
+sub macro_from_name {
+  my ($self, $item) = @_;
+  my $macro = $item->{name};
+  $macro = $item->{value} unless defined $macro;
+  $macro;
+}
+
+# Keep to the traditional perl source macro
+sub memEQ {
+  "memEQ";
+}
+
+sub params {
+  my ($self, $what) = @_;
+  foreach (sort keys %$what) {
+    warn "ExtUtils::Constant doesn't know how to handle values of type $_" unless defined $XS_Constant{$_};
+  }
+  my $params = {};
+  $params->{''} = 1 if $what->{''};
+  $params->{IV} = 1 if $what->{IV} || $what->{UV} || $what->{PVN};
+  $params->{NV} = 1 if $what->{NV};
+  $params->{PV} = 1 if $what->{PV} || $what->{PVN};
+  $params->{SV} = 1 if $what->{SV};
+  return $params;
+}
+
+
+sub C_constant_prefix_param {
+  "aTHX_ ";
+}
+
+sub C_constant_prefix_param_defintion {
+  "pTHX_ ";
+}
+
+sub C_constant_namelen_param_definition {
+  'STRLEN ' . $_[0] -> C_constant_namelen_param;
+}
+
+sub C_constant_param_defintion {
+  my ($self, $params) = @_;
+  my $body = '';
+  $body .= ", int utf8" if $params->{''};
+  $body .= ", IV *iv_return" if $params->{IV};
+  $body .= ", NV *nv_return" if $params->{NV};
+  $body .= ", const char **pv_return" if $params->{PV};
+  $body .= ", SV **sv_return" if $params->{SV};
+  $body;
+}
+
+sub C_constant_param {
+  my ($self, $params) = @_;
+  my $body = '';
+  $body .= ", utf8" if $params->{''};
+  $body .= ", iv_return" if $params->{IV};
+  $body .= ", nv_return" if $params->{NV};
+  $body .= ", pv_return" if $params->{PV};
+  $body .= ", sv_return" if $params->{SV};
+  $body;
+}
+
+sub dogfood {
+  my ($self, $args, @items) = @_;
+  my ($package, $subname, $default_type, $what, $indent, $breakout) =
+    @{$args}{qw(package subname default_type what indent breakout)};
+  my $result = <<"EOT";
+  /* When generated this function returned values for the list of names given
+     in this section of perl code.  Rather than manually editing these functions
+     to add or remove constants, which would result in this comment and section
+     of code becoming inaccurate, we recommend that you edit this section of
+     code, and use it to regenerate a new set of constant functions which you
+     then use to replace the originals.
+
+     Regenerate these constant functions by feeding this entire source file to
+     perl -x
+
+#!$^X -w
+use ExtUtils::Constant qw (constant_types C_constant XS_constant);
+
+EOT
+  $result .= $self->dump_names ({default_type=>$default_type, what=>$what,
+				 indent=>0, declare_types=>1},
+				@items);
+  $result .= <<'EOT';
+
+print constant_types(); # macro defs
+EOT
+  $package = perl_stringify($package);
+  $result .=
+    "foreach (C_constant (\"$package\", '$subname', '$default_type', \$types, ";
+  # The form of the indent parameter isn't defined. (Yet)
+  if (defined $indent) {
+    require Data::Dumper;
+    $Data::Dumper::Terse=1;
+    $Data::Dumper::Terse=1; # Not used once. :-)
+    chomp ($indent = Data::Dumper::Dumper ($indent));
+    $result .= $indent;
+  } else {
+    $result .= 'undef';
+  }
+  $result .= ", $breakout" . ', @names) ) {
+    print $_, "\n"; # C constant subs
+}
+print "#### XS Section:\n";
+print XS_constant ("' . $package . '", $types);
+__END__
+   */
+
+';
+
+  $result;
+}
+
+1;