1 # exponentl.m4 serial 3 2 dnl Copyright (C) 2007-2012 Free Software Foundation, Inc. 3 dnl This file is free software; the Free Software Foundation 4 dnl gives unlimited permission to copy and/or distribute it, 5 dnl with or without modifications, as long as this notice is preserved. 6 AC_DEFUN([gl_LONG_DOUBLE_EXPONENT_LOCATION], 7 [ 8 AC_REQUIRE([gl_BIGENDIAN]) 9 AC_CACHE_CHECK([where to find the exponent in a 'long double'], 10 [gl_cv_cc_long_double_expbit0], 11 [ 12 AC_RUN_IFELSE( 13 [AC_LANG_SOURCE([[ 14 #include <float.h> 15 #include <stddef.h> 16 #include <stdio.h> 17 #include <string.h> 18 #define NWORDS \ 19 ((sizeof (long double) + sizeof (unsigned int) - 1) / sizeof (unsigned int)) 20 typedef union { long double value; unsigned int word[NWORDS]; } 21 memory_long_double; 22 static unsigned int ored_words[NWORDS]; 23 static unsigned int anded_words[NWORDS]; 24 static void add_to_ored_words (long double x) 25 { 26 memory_long_double m; 27 size_t i; 28 /* Clear it first, in case 29 sizeof (long double) < sizeof (memory_long_double). */ 30 memset (&m, 0, sizeof (memory_long_double)); 31 m.value = x; 32 for (i = 0; i < NWORDS; i++) 33 { 34 ored_words[i] |= m.word[i]; 35 anded_words[i] &= m.word[i]; 36 } 37 } 38 int main () 39 { 40 size_t j; 41 FILE *fp = fopen ("conftest.out", "w"); 42 if (fp == NULL) 43 return 1; 44 for (j = 0; j < NWORDS; j++) 45 anded_words[j] = ~ (unsigned int) 0; 46 add_to_ored_words (0.25L); 47 add_to_ored_words (0.5L); 48 add_to_ored_words (1.0L); 49 add_to_ored_words (2.0L); 50 add_to_ored_words (4.0L); 51 /* Remove bits that are common (e.g. if representation of the first mantissa 52 bit is explicit). */ 53 for (j = 0; j < NWORDS; j++) 54 ored_words[j] &= ~anded_words[j]; 55 /* Now find the nonzero word. */ 56 for (j = 0; j < NWORDS; j++) 57 if (ored_words[j] != 0) 58 break; 59 if (j < NWORDS) 60 { 61 size_t i; 62 for (i = j + 1; i < NWORDS; i++) 63 if (ored_words[i] != 0) 64 { 65 fprintf (fp, "unknown"); 66 return (fclose (fp) != 0); 67 } 68 for (i = 0; ; i++) 69 if ((ored_words[j] >> i) & 1) 70 { 71 fprintf (fp, "word %d bit %d", (int) j, (int) i); 72 return (fclose (fp) != 0); 73 } 74 } 75 fprintf (fp, "unknown"); 76 return (fclose (fp) != 0); 77 } 78 ]])], 79 [gl_cv_cc_long_double_expbit0=`cat conftest.out`], 80 [gl_cv_cc_long_double_expbit0="unknown"], 81 [ 82 dnl When cross-compiling, we don't know. It depends on the 83 dnl ABI and compiler version. There are too many cases. 84 gl_cv_cc_long_double_expbit0="unknown" 85 ]) 86 rm -f conftest.out 87 ]) 88 case "$gl_cv_cc_long_double_expbit0" in 89 word*bit*) 90 word=`echo "$gl_cv_cc_long_double_expbit0" | sed -e 's/word //' -e 's/ bit.*//'` 91 bit=`echo "$gl_cv_cc_long_double_expbit0" | sed -e 's/word.*bit //'` 92 AC_DEFINE_UNQUOTED([LDBL_EXPBIT0_WORD], [$word], 93 [Define as the word index where to find the exponent of 'long double'.]) 94 AC_DEFINE_UNQUOTED([LDBL_EXPBIT0_BIT], [$bit], 95 [Define as the bit index in the word where to find bit 0 of the exponent of 'long double'.]) 96 ;; 97 esac 98 ]) 99
