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Diffstat (limited to 'm4')
| -rw-r--r-- | m4/ax_c_float_words_bigendian.m4 | 83 |
1 files changed, 83 insertions, 0 deletions
diff --git a/m4/ax_c_float_words_bigendian.m4 b/m4/ax_c_float_words_bigendian.m4 new file mode 100644 index 0000000..216b90d --- /dev/null +++ b/m4/ax_c_float_words_bigendian.m4 @@ -0,0 +1,83 @@ +# =============================================================================== +# 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 <dan@amelang.net> +# +# 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 |