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# ===============================================================================
# https://www.gnu.org/software/autoconf-archive/ax_prog_cc_char_subscripts.html
# ===============================================================================
#
# SYNOPSIS
#
# AX_PROG_CC_CHAR_SUBSCRIPTS(substvar [,hard])
#
# DESCRIPTION
#
# Try to find a compiler option that enables usage of char-type to index a
# value-field. This one needs unsigned-chars and it must suppress warnings
# about usage of chars for subscripting. for gcc -funsigned-char
# -Wno-char-subscripts
#
# Currently this macro knows about GCC. hopefully will evolve to use:
# Solaris C compiler, Digital Unix C compiler, C for AIX Compiler, HP-UX C
# compiler, and IRIX C compiler.
#
# LICENSE
#
# Copyright (c) 2008 Guido U. Draheim <guidod@gmx.de>
#
# Copying and distribution of this file, with or without modification, are
# permitted in any medium without royalty provided the copyright notice
# and this notice are preserved. This file is offered as-is, without any
# warranty.
#serial 9
AU_ALIAS([AC_PROG_CC_CHAR_SUBSCRIPTS], [AX_PROG_CC_CHAR_SUBSCRIPTS])
AC_DEFUN([AX_PROG_CC_CHAR_SUBSCRIPTS], [
pushdef([CV],ac_cv_prog_cc_char_subscripts)dnl
hard=$2
if test -z "$hard"; then
msg="C to enable char subscripts"
else
msg="C to ensure char subscripts"
fi
AC_CACHE_CHECK($msg, CV, [
cat > conftest.c <<EOF
int main (void)
{
char v = 1;
int x[[2]] = { 3 , 4 };
return x[[v]];
}
EOF
cp conftest.c writetest.c
dnl GCC
if test "$GCC" = "yes";
then
if test -z "$hard"; then
CV="-funsigned-char -Wno-char-subscripts"
else
CV="-funsigned-char -Wno-char-subscripts"
fi
if test -n "`${CC-cc} -c $CV conftest.c 2>&1`" ; then
CV="suppressed: did not work"
fi
dnl Solaris C compiler
# Solaris sunpro has no option for unsignedchar but
# signedchar is the default for char. Duhh.
dnl HP-UX C compiler
dnl Digital Unix C compiler
elif ! $CC > /dev/null 2>&1 &&
$CC -c -unsigned conftest.c > /dev/null 2>&1 &&
test -f conftest.o
then
# char : unsigned char
CV="-unsigned"
rm conftest.o
if test -n "`${CC-cc} -c $CV conftest.c 2>&1`" ; then
CV="suppressed: did not work"
fi
dnl C for AIX Compiler
dnl IRIX C compiler
# char is unsigned by default for IRIX C.
fi
rm -f conftest.*
])
if test -z "[$]$1" ; then
if test -n "$CV" ; then
case "$CV" in
suppressed*) $1="" ;; # known but suppressed
*) $1="$CV" ;;
esac
fi
fi
AC_SUBST($1)
popdef([CV])dnl
])
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