Hexadecimal float literals, for perl #122219

Do not use system strtod/strtold since its C99 (which we do not require).

If we can fit the mantissa bits of a NV to a UV (which is the case for
the most common format, 64-bit IEEE 754 double, which has 52 mantissa bits)
we will use that, and only in the end convert to NV.  If we cannot fit
the bits, accumulate the bits incrementally to a NV.

1 files changed, 9 insertions, 0 deletions

diff --git a/pod/perldata.pod b/pod/perldata.pod
index d8edfe94f1..fe39783dd3 100644
--- a/pod/perldata.pod
+++ b/pod/perldata.pod
@@ -402,6 +402,7 @@ integer formats:
     0xdead_beef         # more hex   
     0377                # octal (only numbers, begins with 0)
     0b011011            # binary
+    0x1.999ap-4         # hexadecimal floating point (the 'p' is required)
 
 You are allowed to use underscores (underbars) in numeric literals
 between digits for legibility (but not multiple underscores in a row:
@@ -425,6 +426,14 @@ Hexadecimal, octal, or binary, representations in string literals
 representation.  The hex() and oct() functions make these conversions
 for you.  See L<perlfunc/hex> and L<perlfunc/oct> for more details.
 
+Hexadecimal floating point can start just like a hexadecimal literal,
+and it can be followed by an optional fractional hexadecimal part,
+but it must be followed by C<p>, an optional sign, and a power of two.
+The format is useful for accurately presenting floating point values,
+avoiding conversions to or from decimal floating point, and therefore
+avoiding possible loss in precision.  Notice that while most current
+platforms use the 64-bit IEEE 754 floating point, not all do.
+
 You can also embed newlines directly in your strings, i.e., they can end
 on a different line than they begin.  This is nice, but if you forget
 your trailing quote, the error will not be reported until Perl finds