1 # exponentf.m4 serial 2 2 dnl Copyright (C) 2007-2008, 2010-2012 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_FLOAT_EXPONENT_LOCATION], 7 [ 8 AC_CACHE_CHECK([where to find the exponent in a 'float'], 9 [gl_cv_cc_float_expbit0], 10 [ 11 AC_RUN_IFELSE( 12 [AC_LANG_SOURCE([[ 13 #include <float.h> 14 #include <stddef.h> 15 #include <stdio.h> 16 #include <string.h> 17 #define NWORDS \ 18 ((sizeof (float) + sizeof (unsigned int) - 1) / sizeof (unsigned int)) 19 typedef union { float value; unsigned int word[NWORDS]; } memory_float; 20 static unsigned int ored_words[NWORDS]; 21 static unsigned int anded_words[NWORDS]; 22 static void add_to_ored_words (float x) 23 { 24 memory_float m; 25 size_t i; 26 /* Clear it first, in case 27 sizeof (float) < sizeof (memory_float). */ 28 memset (&m, 0, sizeof (memory_float)); 29 m.value = x; 30 for (i = 0; i < NWORDS; i++) 31 { 32 ored_words[i] |= m.word[i]; 33 anded_words[i] &= m.word[i]; 34 } 35 } 36 int main () 37 { 38 size_t j; 39 FILE *fp = fopen ("conftest.out", "w"); 40 if (fp == NULL) 41 return 1; 42 for (j = 0; j < NWORDS; j++) 43 anded_words[j] = ~ (unsigned int) 0; 44 add_to_ored_words (0.25f); 45 add_to_ored_words (0.5f); 46 add_to_ored_words (1.0f); 47 add_to_ored_words (2.0f); 48 add_to_ored_words (4.0f); 49 /* Remove bits that are common (e.g. if representation of the first mantissa 50 bit is explicit). */ 51 for (j = 0; j < NWORDS; j++) 52 ored_words[j] &= ~anded_words[j]; 53 /* Now find the nonzero word. */ 54 for (j = 0; j < NWORDS; j++) 55 if (ored_words[j] != 0) 56 break; 57 if (j < NWORDS) 58 { 59 size_t i; 60 for (i = j + 1; i < NWORDS; i++) 61 if (ored_words[i] != 0) 62 { 63 fprintf (fp, "unknown"); 64 return (fclose (fp) != 0); 65 } 66 for (i = 0; ; i++) 67 if ((ored_words[j] >> i) & 1) 68 { 69 fprintf (fp, "word %d bit %d", (int) j, (int) i); 70 return (fclose (fp) != 0); 71 } 72 } 73 fprintf (fp, "unknown"); 74 return (fclose (fp) != 0); 75 } 76 ]])], 77 [gl_cv_cc_float_expbit0=`cat conftest.out`], 78 [gl_cv_cc_float_expbit0="unknown"], 79 [gl_cv_cc_float_expbit0="word 0 bit 23"]) 80 rm -f conftest.out 81 ]) 82 case "$gl_cv_cc_float_expbit0" in 83 word*bit*) 84 word=`echo "$gl_cv_cc_float_expbit0" | sed -e 's/word //' -e 's/ bit.*//'` 85 bit=`echo "$gl_cv_cc_float_expbit0" | sed -e 's/word.*bit //'` 86 AC_DEFINE_UNQUOTED([FLT_EXPBIT0_WORD], [$word], 87 [Define as the word index where to find the exponent of 'float'.]) 88 AC_DEFINE_UNQUOTED([FLT_EXPBIT0_BIT], [$bit], 89 [Define as the bit index in the word where to find bit 0 of the exponent of 'float'.]) 90 ;; 91 esac 92 ]) 93
