1# exponentl.m4 serial 5 2dnl Copyright (C) 2007-2022 Free Software Foundation, Inc. 3dnl This file is free software; the Free Software Foundation 4dnl gives unlimited permission to copy and/or distribute it, 5dnl with or without modifications, as long as this notice is preserved. 6AC_DEFUN([gl_LONG_DOUBLE_EXPONENT_LOCATION], 7[ 8 AC_REQUIRE([gl_BIGENDIAN]) 9 AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles 10 AC_CACHE_CHECK([where to find the exponent in a 'long double'], 11 [gl_cv_cc_long_double_expbit0], 12 [ 13 AC_RUN_IFELSE( 14 [AC_LANG_SOURCE([[ 15#include <float.h> 16#include <stddef.h> 17#include <stdio.h> 18#include <string.h> 19#define NWORDS \ 20 ((sizeof (long double) + sizeof (unsigned int) - 1) / sizeof (unsigned int)) 21typedef union { long double value; unsigned int word[NWORDS]; } 22 memory_long_double; 23static unsigned int ored_words[NWORDS]; 24static unsigned int anded_words[NWORDS]; 25static void add_to_ored_words (long double *x) 26{ 27 memory_long_double m; 28 size_t i; 29 /* Clear it first, in case 30 sizeof (long double) < sizeof (memory_long_double). */ 31 memset (&m, 0, sizeof (memory_long_double)); 32 m.value = *x; 33 for (i = 0; i < NWORDS; i++) 34 { 35 ored_words[i] |= m.word[i]; 36 anded_words[i] &= m.word[i]; 37 } 38} 39int main () 40{ 41 static long double samples[5] = { 0.25L, 0.5L, 1.0L, 2.0L, 4.0L }; 42 size_t j; 43 FILE *fp = fopen ("conftest.out", "w"); 44 if (fp == NULL) 45 return 1; 46 for (j = 0; j < NWORDS; j++) 47 anded_words[j] = ~ (unsigned int) 0; 48 for (j = 0; j < 5; j++) 49 add_to_ored_words (&samples[j]); 50 /* Remove bits that are common (e.g. if representation of the first mantissa 51 bit is explicit). */ 52 for (j = 0; j < NWORDS; j++) 53 ored_words[j] &= ~anded_words[j]; 54 /* Now find the nonzero word. */ 55 for (j = 0; j < NWORDS; j++) 56 if (ored_words[j] != 0) 57 break; 58 if (j < NWORDS) 59 { 60 size_t i; 61 for (i = j + 1; i < NWORDS; i++) 62 if (ored_words[i] != 0) 63 { 64 fprintf (fp, "unknown"); 65 return (fclose (fp) != 0); 66 } 67 for (i = 0; ; i++) 68 if ((ored_words[j] >> i) & 1) 69 { 70 fprintf (fp, "word %d bit %d", (int) j, (int) i); 71 return (fclose (fp) != 0); 72 } 73 } 74 fprintf (fp, "unknown"); 75 return (fclose (fp) != 0); 76} 77 ]])], 78 [gl_cv_cc_long_double_expbit0=`cat conftest.out`], 79 [gl_cv_cc_long_double_expbit0="unknown"], 80 [ 81 dnl When cross-compiling, in general we don't know. It depends on the 82 dnl ABI and compiler version. There are too many cases. 83 gl_cv_cc_long_double_expbit0="unknown" 84 case "$host_os" in 85 mingw*) # On native Windows (little-endian), we know the result 86 # in two cases: mingw, MSVC. 87 AC_EGREP_CPP([Known], [ 88#ifdef __MINGW32__ 89 Known 90#endif 91 ], [gl_cv_cc_long_double_expbit0="word 2 bit 0"]) 92 AC_EGREP_CPP([Known], [ 93#ifdef _MSC_VER 94 Known 95#endif 96 ], [gl_cv_cc_long_double_expbit0="word 1 bit 20"]) 97 ;; 98 esac 99 ]) 100 rm -f conftest.out 101 ]) 102 case "$gl_cv_cc_long_double_expbit0" in 103 word*bit*) 104 word=`echo "$gl_cv_cc_long_double_expbit0" | sed -e 's/word //' -e 's/ bit.*//'` 105 bit=`echo "$gl_cv_cc_long_double_expbit0" | sed -e 's/word.*bit //'` 106 AC_DEFINE_UNQUOTED([LDBL_EXPBIT0_WORD], [$word], 107 [Define as the word index where to find the exponent of 'long double'.]) 108 AC_DEFINE_UNQUOTED([LDBL_EXPBIT0_BIT], [$bit], 109 [Define as the bit index in the word where to find bit 0 of the exponent of 'long double'.]) 110 ;; 111 esac 112]) 113