mirror of https://github.com/python/cpython
84 lines
3.1 KiB
Plaintext
84 lines
3.1 KiB
Plaintext
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# ===============================================================================
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# https://www.gnu.org/software/autoconf-archive/ax_c_float_words_bigendian.html
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# ===============================================================================
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#
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# SYNOPSIS
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#
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# AX_C_FLOAT_WORDS_BIGENDIAN([ACTION-IF-TRUE], [ACTION-IF-FALSE], [ACTION-IF-UNKNOWN])
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#
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# DESCRIPTION
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#
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# Checks the ordering of words within a multi-word float. This check is
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# necessary because on some systems (e.g. certain ARM systems), the float
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# word ordering can be different from the byte ordering. In a multi-word
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# float context, "big-endian" implies that the word containing the sign
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# bit is found in the memory location with the lowest address. This
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# implementation was inspired by the AC_C_BIGENDIAN macro in autoconf.
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#
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# The endianness is detected by first compiling C code that contains a
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# special double float value, then grepping the resulting object file for
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# certain strings of ASCII values. The double is specially crafted to have
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# a binary representation that corresponds with a simple string. In this
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# implementation, the string "noonsees" was selected because the
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# individual word values ("noon" and "sees") are palindromes, thus making
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# this test byte-order agnostic. If grep finds the string "noonsees" in
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# the object file, the target platform stores float words in big-endian
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# order. If grep finds "seesnoon", float words are in little-endian order.
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# If neither value is found, the user is instructed to specify the
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# ordering.
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#
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# LICENSE
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#
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# Copyright (c) 2008 Daniel Amelang <dan@amelang.net>
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#
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# Copying and distribution of this file, with or without modification, are
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# permitted in any medium without royalty provided the copyright notice
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# and this notice are preserved. This file is offered as-is, without any
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# warranty.
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#serial 11
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AC_DEFUN([AX_C_FLOAT_WORDS_BIGENDIAN],
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[AC_CACHE_CHECK(whether float word ordering is bigendian,
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ax_cv_c_float_words_bigendian, [
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ax_cv_c_float_words_bigendian=unknown
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AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
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double d = 90904234967036810337470478905505011476211692735615632014797120844053488865816695273723469097858056257517020191247487429516932130503560650002327564517570778480236724525140520121371739201496540132640109977779420565776568942592.0;
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]])], [
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if grep noonsees conftest.$ac_objext >/dev/null ; then
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ax_cv_c_float_words_bigendian=yes
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fi
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if grep seesnoon conftest.$ac_objext >/dev/null ; then
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if test "$ax_cv_c_float_words_bigendian" = unknown; then
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ax_cv_c_float_words_bigendian=no
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else
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ax_cv_c_float_words_bigendian=unknown
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fi
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fi
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])])
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case $ax_cv_c_float_words_bigendian in
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yes)
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m4_default([$1],
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[AC_DEFINE([FLOAT_WORDS_BIGENDIAN], 1,
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[Define to 1 if your system stores words within floats
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with the most significant word first])]) ;;
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no)
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$2 ;;
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*)
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m4_default([$3],
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[AC_MSG_ERROR([
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Unknown float word ordering. You need to manually preset
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ax_cv_c_float_words_bigendian=no (or yes) according to your system.
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])]) ;;
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esac
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])# AX_C_FLOAT_WORDS_BIGENDIAN
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