1 # exponentd.m4 serial 3 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_DOUBLE_EXPONENT_LOCATION], 7 [ 8 AC_CACHE_CHECK([where to find the exponent in a 'double'], 9 [gl_cv_cc_double_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 (double) + sizeof (unsigned int) - 1) / sizeof (unsigned int)) 19 typedef union { double value; unsigned int word[NWORDS]; } memory_double; 20 static unsigned int ored_words[NWORDS]; 21 static unsigned int anded_words[NWORDS]; 22 static void add_to_ored_words (double x) 23 { 24 memory_double m; 25 size_t i; 26 /* Clear it first, in case sizeof (double) < sizeof (memory_double). */ 27 memset (&m, 0, sizeof (memory_double)); 28 m.value = x; 29 for (i = 0; i < NWORDS; i++) 30 { 31 ored_words[i] |= m.word[i]; 32 anded_words[i] &= m.word[i]; 33 } 34 } 35 int main () 36 { 37 size_t j; 38 FILE *fp = fopen ("conftest.out", "w"); 39 if (fp == NULL) 40 return 1; 41 for (j = 0; j < NWORDS; j++) 42 anded_words[j] = ~ (unsigned int) 0; 43 add_to_ored_words (0.25); 44 add_to_ored_words (0.5); 45 add_to_ored_words (1.0); 46 add_to_ored_words (2.0); 47 add_to_ored_words (4.0); 48 /* Remove bits that are common (e.g. if representation of the first mantissa 49 bit is explicit). */ 50 for (j = 0; j < NWORDS; j++) 51 ored_words[j] &= ~anded_words[j]; 52 /* Now find the nonzero word. */ 53 for (j = 0; j < NWORDS; j++) 54 if (ored_words[j] != 0) 55 break; 56 if (j < NWORDS) 57 { 58 size_t i; 59 for (i = j + 1; i < NWORDS; i++) 60 if (ored_words[i] != 0) 61 { 62 fprintf (fp, "unknown"); 63 return (fclose (fp) != 0); 64 } 65 for (i = 0; ; i++) 66 if ((ored_words[j] >> i) & 1) 67 { 68 fprintf (fp, "word %d bit %d", (int) j, (int) i); 69 return (fclose (fp) != 0); 70 } 71 } 72 fprintf (fp, "unknown"); 73 return (fclose (fp) != 0); 74 } 75 ]])], 76 [gl_cv_cc_double_expbit0=`cat conftest.out`], 77 [gl_cv_cc_double_expbit0="unknown"], 78 [ 79 dnl On ARM, there are two 'double' floating-point formats, used by 80 dnl different sets of instructions: The older FPA instructions assume 81 dnl that they are stored in big-endian word order, while the words 82 dnl (like integer types) are stored in little-endian byte order. 83 dnl The newer VFP instructions assume little-endian order 84 dnl consistently. 85 AC_EGREP_CPP([mixed_endianness], [ 86 #if defined arm || defined __arm || defined __arm__ 87 mixed_endianness 88 #endif 89 ], 90 [gl_cv_cc_double_expbit0="unknown"], 91 [ 92 pushdef([AC_MSG_CHECKING],[:])dnl 93 pushdef([AC_MSG_RESULT],[:])dnl 94 pushdef([AC_MSG_RESULT_UNQUOTED],[:])dnl 95 AC_C_BIGENDIAN( 96 [gl_cv_cc_double_expbit0="word 0 bit 20"], 97 [gl_cv_cc_double_expbit0="word 1 bit 20"], 98 [gl_cv_cc_double_expbit0="unknown"]) 99 popdef([AC_MSG_RESULT_UNQUOTED])dnl 100 popdef([AC_MSG_RESULT])dnl 101 popdef([AC_MSG_CHECKING])dnl 102 ]) 103 ]) 104 rm -f conftest.out 105 ]) 106 case "$gl_cv_cc_double_expbit0" in 107 word*bit*) 108 word=`echo "$gl_cv_cc_double_expbit0" | sed -e 's/word //' -e 's/ bit.*//'` 109 bit=`echo "$gl_cv_cc_double_expbit0" | sed -e 's/word.*bit //'` 110 AC_DEFINE_UNQUOTED([DBL_EXPBIT0_WORD], [$word], 111 [Define as the word index where to find the exponent of 'double'.]) 112 AC_DEFINE_UNQUOTED([DBL_EXPBIT0_BIT], [$bit], 113 [Define as the bit index in the word where to find bit 0 of the exponent of 'double'.]) 114 ;; 115 esac 116 ]) 117
