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ax_c_float_words_bigendian.m4
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ax_c_float_words_bigendian.m4
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# ===============================================================================
# https://www.gnu.org/software/autoconf-archive/ax_c_float_words_bigendian.html
# ===============================================================================
#
# SYNOPSIS
#
# AX_C_FLOAT_WORDS_BIGENDIAN([ACTION-IF-TRUE], [ACTION-IF-FALSE], [ACTION-IF-UNKNOWN])
#
# DESCRIPTION
#
# Checks the ordering of words within a multi-word float. This check is
# necessary because on some systems (e.g. certain ARM systems), the float
# word ordering can be different from the byte ordering. In a multi-word
# float context, "big-endian" implies that the word containing the sign
# bit is found in the memory location with the lowest address. This
# implementation was inspired by the AC_C_BIGENDIAN macro in autoconf.
#
# The endianness is detected by first compiling C code that contains a
# special double float value, then grepping the resulting object file for
# certain strings of ASCII values. The double is specially crafted to have
# a binary representation that corresponds with a simple string. In this
# implementation, the string "noonsees" was selected because the
# individual word values ("noon" and "sees") are palindromes, thus making
# this test byte-order agnostic. If grep finds the string "noonsees" in
# the object file, the target platform stores float words in big-endian
# order. If grep finds "seesnoon", float words are in little-endian order.
# If neither value is found, the user is instructed to specify the
# ordering.
#
# LICENSE
#
# Copyright (c) 2008 Daniel Amelang <[email protected]>
#
# 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 11
AC_DEFUN([AX_C_FLOAT_WORDS_BIGENDIAN],
[AC_CACHE_CHECK(whether float word ordering is bigendian,
ax_cv_c_float_words_bigendian, [
ax_cv_c_float_words_bigendian=unknown
AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
double d = 90904234967036810337470478905505011476211692735615632014797120844053488865816695273723469097858056257517020191247487429516932130503560650002327564517570778480236724525140520121371739201496540132640109977779420565776568942592.0;
]])], [
if grep noonsees conftest.$ac_objext >/dev/null ; then
ax_cv_c_float_words_bigendian=yes
fi
if grep seesnoon conftest.$ac_objext >/dev/null ; then
if test "$ax_cv_c_float_words_bigendian" = unknown; then
ax_cv_c_float_words_bigendian=no
else
ax_cv_c_float_words_bigendian=unknown
fi
fi
])])
case $ax_cv_c_float_words_bigendian in
yes)
m4_default([$1],
[AC_DEFINE([FLOAT_WORDS_BIGENDIAN], 1,
[Define to 1 if your system stores words within floats
with the most significant word first])]) ;;
no)
$2 ;;
*)
m4_default([$3],
[AC_MSG_ERROR([
Unknown float word ordering. You need to manually preset
ax_cv_c_float_words_bigendian=no (or yes) according to your system.
])]) ;;
esac
])# AX_C_FLOAT_WORDS_BIGENDIAN