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Add patch for ax_c_float_words_bigendian.m4 to autoconf-archive#23
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erlend-aasland merged 1 commit intopython:mainfromerlend-aasland:ax-c-float-words-bigendianOct 16, 2024
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,92 @@ | ||
| diff --git a/m4/ax_c_float_words_bigendian.m4 b/m4/ax_c_float_words_bigendian.m4 | ||
| index 216b90d8..52036844 100644 | ||
| --- a/m4/ax_c_float_words_bigendian.m4 | ||
| +++ b/m4/ax_c_float_words_bigendian.m4 | ||
| @@ -27,32 +27,81 @@ | ||
| # If neither value is found, the user is instructed to specify the | ||
| # ordering. | ||
| # | ||
| +# Early versions of this macro (i.e., before serial 12) would not work | ||
| +# when interprocedural optimization (via link-time optimization) was | ||
| +# enabled. This would happen when, say, the GCC/clang "-flto" flag, or the | ||
| +# ICC "-ipo" flag was used, for example. The problem was that under | ||
| +# these conditions, the compiler did not allocate for and write the special | ||
| +# float value in the data segment of the object file, since doing so might | ||
| +# not prove optimal once more context was available. Thus, the special value | ||
| +# (in platform-dependent binary form) could not be found in the object file, | ||
| +# and the macro would fail. | ||
| +# | ||
| +# The solution to the above problem was to: | ||
| +# | ||
| +# 1) Compile and link a whole test program rather than just compile an | ||
| +# object file. This ensures that we reach the point where even an | ||
| +# interprocedural optimizing compiler writes values to the data segment. | ||
| +# | ||
| +# 2) Add code that requires the compiler to write the special value to | ||
| +# the data segment, as opposed to "optimizing away" the variable's | ||
| +# allocation. This could be done via compiler keywords or options, but | ||
| +# it's tricky to make this work for all versions of all compilers with | ||
| +# all optimization settings. The chosen solution was to make the exit | ||
| +# code of the test program depend on the storing of the special value | ||
| +# in memory (in the data segment). Because the exit code can be | ||
| +# verified, any compiler that aspires to be correct will produce a | ||
| +# program binary that contains the value, which the macro can then find. | ||
| +# | ||
| +# How does the exit code depend on the special value residing in memory? | ||
| +# Memory, unlike variables and registers, can be addressed indirectly at run | ||
| +# time. The exit code of this test program is a result of indirectly reading | ||
| +# and writing to the memory region where the special value is supposed to | ||
| +# reside. The actual memory addresses used and the values to be written are | ||
| +# derived from the the program input ("argv") and are therefore not known at | ||
| +# compile or link time. The compiler has no choice but to defer the | ||
| +# computation to run time, and to prepare by allocating and populating the | ||
| +# data segment with the special value. For further details, refer to the | ||
| +# source code of the test program. | ||
| +# | ||
| +# Note that the test program is never meant to be run. It only exists to host | ||
| +# a double float value in a given platform's binary format. Thus, error | ||
| +# handling is not included. | ||
| +# | ||
| # LICENSE | ||
| # | ||
| -# Copyright (c) 2008 Daniel Amelang <dan@amelang.net> | ||
| +# Copyright (c) 2008, 2023 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 | ||
| +#serial 12 | ||
| 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([[ | ||
| +AC_LINK_IFELSE([AC_LANG_SOURCE([[ | ||
| + | ||
| +#include <stdlib.h> | ||
| + | ||
| +static double m[] = {9.090423496703681e+223, 0.0}; | ||
| -double d = 90904234967036810337470478905505011476211692735615632014797120844053488865816695273723469097858056257517020191247487429516932130503560650002327564517570778480236724525140520121371739201496540132640109977779420565776568942592.0; | ||
| +int main (int argc, char *argv[]) | ||
| +{ | ||
| + m[atoi (argv[1])] += atof (argv[2]); | ||
| + return m[atoi (argv[3])] > 0.0; | ||
| +} | ||
| ]])], [ | ||
| -if grep noonsees conftest.$ac_objext >/dev/null ; then | ||
| +if grep noonsees conftest$EXEEXT >/dev/null ; then | ||
| ax_cv_c_float_words_bigendian=yes | ||
| fi | ||
| -if grep seesnoon conftest.$ac_objext >/dev/null ; then | ||
| +if grep seesnoon conftest$EXEEXT >/dev/null ; then | ||
| if test "$ax_cv_c_float_words_bigendian" = unknown; then | ||
| ax_cv_c_float_words_bigendian=no | ||
| else |
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