Ross Burton | 2a9c380 | 2018-09-19 07:25:48 +0100 | [diff] [blame] | 1 | # =============================================================================== |
| 2 | # https://www.gnu.org/software/autoconf-archive/ax_c_float_words_bigendian.html |
| 3 | # =============================================================================== |
| 4 | # |
| 5 | # SYNOPSIS |
| 6 | # |
| 7 | # AX_C_FLOAT_WORDS_BIGENDIAN([ACTION-IF-TRUE], [ACTION-IF-FALSE], [ACTION-IF-UNKNOWN]) |
| 8 | # |
| 9 | # DESCRIPTION |
| 10 | # |
| 11 | # Checks the ordering of words within a multi-word float. This check is |
| 12 | # necessary because on some systems (e.g. certain ARM systems), the float |
| 13 | # word ordering can be different from the byte ordering. In a multi-word |
| 14 | # float context, "big-endian" implies that the word containing the sign |
| 15 | # bit is found in the memory location with the lowest address. This |
| 16 | # implementation was inspired by the AC_C_BIGENDIAN macro in autoconf. |
| 17 | # |
| 18 | # The endianness is detected by first compiling C code that contains a |
| 19 | # special double float value, then grepping the resulting object file for |
| 20 | # certain strings of ASCII values. The double is specially crafted to have |
| 21 | # a binary representation that corresponds with a simple string. In this |
| 22 | # implementation, the string "noonsees" was selected because the |
| 23 | # individual word values ("noon" and "sees") are palindromes, thus making |
| 24 | # this test byte-order agnostic. If grep finds the string "noonsees" in |
| 25 | # the object file, the target platform stores float words in big-endian |
| 26 | # order. If grep finds "seesnoon", float words are in little-endian order. |
| 27 | # If neither value is found, the user is instructed to specify the |
| 28 | # ordering. |
| 29 | # |
| 30 | # LICENSE |
| 31 | # |
| 32 | # Copyright (c) 2008 Daniel Amelang <dan@amelang.net> |
| 33 | # |
| 34 | # Copying and distribution of this file, with or without modification, are |
| 35 | # permitted in any medium without royalty provided the copyright notice |
| 36 | # and this notice are preserved. This file is offered as-is, without any |
| 37 | # warranty. |
| 38 | |
| 39 | #serial 11 |
| 40 | |
| 41 | AC_DEFUN([AX_C_FLOAT_WORDS_BIGENDIAN], |
| 42 | [AC_CACHE_CHECK(whether float word ordering is bigendian, |
| 43 | ax_cv_c_float_words_bigendian, [ |
| 44 | |
| 45 | ax_cv_c_float_words_bigendian=unknown |
| 46 | AC_COMPILE_IFELSE([AC_LANG_SOURCE([[ |
| 47 | |
| 48 | double d = 90904234967036810337470478905505011476211692735615632014797120844053488865816695273723469097858056257517020191247487429516932130503560650002327564517570778480236724525140520121371739201496540132640109977779420565776568942592.0; |
| 49 | |
| 50 | ]])], [ |
| 51 | |
Arnon Yaari | 5dd8360 | 2020-04-01 18:19:09 +0300 | [diff] [blame] | 52 | if $GREP noonsees conftest.$ac_objext >/dev/null ; then |
Ross Burton | 2a9c380 | 2018-09-19 07:25:48 +0100 | [diff] [blame] | 53 | ax_cv_c_float_words_bigendian=yes |
| 54 | fi |
Arnon Yaari | 5dd8360 | 2020-04-01 18:19:09 +0300 | [diff] [blame] | 55 | if $GREP seesnoon conftest.$ac_objext >/dev/null ; then |
Ross Burton | 2a9c380 | 2018-09-19 07:25:48 +0100 | [diff] [blame] | 56 | if test "$ax_cv_c_float_words_bigendian" = unknown; then |
| 57 | ax_cv_c_float_words_bigendian=no |
| 58 | else |
| 59 | ax_cv_c_float_words_bigendian=unknown |
| 60 | fi |
| 61 | fi |
| 62 | |
| 63 | ])]) |
| 64 | |
| 65 | case $ax_cv_c_float_words_bigendian in |
| 66 | yes) |
| 67 | m4_default([$1], |
| 68 | [AC_DEFINE([FLOAT_WORDS_BIGENDIAN], 1, |
| 69 | [Define to 1 if your system stores words within floats |
| 70 | with the most significant word first])]) ;; |
| 71 | no) |
| 72 | $2 ;; |
| 73 | *) |
| 74 | m4_default([$3], |
| 75 | [AC_MSG_ERROR([ |
| 76 | |
| 77 | Unknown float word ordering. You need to manually preset |
| 78 | ax_cv_c_float_words_bigendian=no (or yes) according to your system. |
| 79 | |
| 80 | ])]) ;; |
| 81 | esac |
| 82 | |
| 83 | ])# AX_C_FLOAT_WORDS_BIGENDIAN |