| 1 | # exponentf.m4 serial 2 |
| 2 | dnl Copyright (C) 2007-2008, 2010-2014 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 | ]) |