diff options
| -rw-r--r-- | Misc/NEWS.d/next/Build/2018-09-18-16-28-31.bpo-34585.CGMu0h.rst | 3 | ||||
| -rw-r--r-- | configure.ac | 76 | ||||
| -rw-r--r-- | m4/ax_c_float_words_bigendian.m4 | 83 |
3 files changed, 99 insertions, 63 deletions
diff --git a/Misc/NEWS.d/next/Build/2018-09-18-16-28-31.bpo-34585.CGMu0h.rst b/Misc/NEWS.d/next/Build/2018-09-18-16-28-31.bpo-34585.CGMu0h.rst new file mode 100644 index 0000000..01318e6 --- /dev/null +++ b/Misc/NEWS.d/next/Build/2018-09-18-16-28-31.bpo-34585.CGMu0h.rst @@ -0,0 +1,3 @@ +Check for floating-point byte order in configure.ac using compilation tests +instead of executing code, so that these checks work in cross-compiled +builds. diff --git a/configure.ac b/configure.ac index 03638f8..96331ec 100644 --- a/configure.ac +++ b/configure.ac @@ -4206,74 +4206,24 @@ fi # * Check for various properties of floating point * # ************************************************** -AC_MSG_CHECKING(whether C doubles are little-endian IEEE 754 binary64) -AC_CACHE_VAL(ac_cv_little_endian_double, [ -AC_RUN_IFELSE([AC_LANG_SOURCE([[ -#include <string.h> -int main() { - double x = 9006104071832581.0; - if (memcmp(&x, "\x05\x04\x03\x02\x01\xff\x3f\x43", 8) == 0) - return 0; - else - return 1; -} -]])], -[ac_cv_little_endian_double=yes], -[ac_cv_little_endian_double=no], -[ac_cv_little_endian_double=no])]) -AC_MSG_RESULT($ac_cv_little_endian_double) -if test "$ac_cv_little_endian_double" = yes -then - AC_DEFINE(DOUBLE_IS_LITTLE_ENDIAN_IEEE754, 1, - [Define if C doubles are 64-bit IEEE 754 binary format, stored - with the least significant byte first]) -fi - -AC_MSG_CHECKING(whether C doubles are big-endian IEEE 754 binary64) -AC_CACHE_VAL(ac_cv_big_endian_double, [ -AC_RUN_IFELSE([AC_LANG_SOURCE([[ -#include <string.h> -int main() { - double x = 9006104071832581.0; - if (memcmp(&x, "\x43\x3f\xff\x01\x02\x03\x04\x05", 8) == 0) - return 0; - else - return 1; -} -]])], -[ac_cv_big_endian_double=yes], -[ac_cv_big_endian_double=no], -[ac_cv_big_endian_double=no])]) -AC_MSG_RESULT($ac_cv_big_endian_double) -if test "$ac_cv_big_endian_double" = yes +AX_C_FLOAT_WORDS_BIGENDIAN +if test "$ax_cv_c_float_words_bigendian" = "yes" then AC_DEFINE(DOUBLE_IS_BIG_ENDIAN_IEEE754, 1, [Define if C doubles are 64-bit IEEE 754 binary format, stored with the most significant byte first]) -fi - -# Some ARM platforms use a mixed-endian representation for doubles. -# While Python doesn't currently have full support for these platforms -# (see e.g., issue 1762561), we can at least make sure that float <-> string -# conversions work. -AC_MSG_CHECKING(whether C doubles are ARM mixed-endian IEEE 754 binary64) -AC_CACHE_VAL(ac_cv_mixed_endian_double, [ -AC_RUN_IFELSE([AC_LANG_SOURCE([[ -#include <string.h> -int main() { - double x = 9006104071832581.0; - if (memcmp(&x, "\x01\xff\x3f\x43\x05\x04\x03\x02", 8) == 0) - return 0; - else - return 1; -} -]])], -[ac_cv_mixed_endian_double=yes], -[ac_cv_mixed_endian_double=no], -[ac_cv_mixed_endian_double=no])]) -AC_MSG_RESULT($ac_cv_mixed_endian_double) -if test "$ac_cv_mixed_endian_double" = yes +elif test "$ax_cv_c_float_words_bigendian" = "no" then + AC_DEFINE(DOUBLE_IS_LITTLE_ENDIAN_IEEE754, 1, + [Define if C doubles are 64-bit IEEE 754 binary format, stored + with the least significant byte first]) +else + # Some ARM platforms use a mixed-endian representation for doubles. + # While Python doesn't currently have full support for these platforms + # (see e.g., issue 1762561), we can at least make sure that float <-> string + # conversions work. + # FLOAT_WORDS_BIGENDIAN doesnt actually detect this case, but if it's not big + # or little, then it must be this? AC_DEFINE(DOUBLE_IS_ARM_MIXED_ENDIAN_IEEE754, 1, [Define if C doubles are 64-bit IEEE 754 binary format, stored in ARM mixed-endian order (byte order 45670123)]) 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 |