# exponentf.m4 serial 2

dnl Copyright (C) 2007-2008, 2010-2018 Free Software Foundation, Inc.

dnl This file is free software; the Free Software Foundation

dnl gives unlimited permission to copy and/or distribute it,

dnl with or without modifications, as long as this notice is preserved.

AC_DEFUN([gl_FLOAT_EXPONENT_LOCATION],

[

  AC_CACHE_CHECK([where to find the exponent in a 'float'],

    [gl_cv_cc_float_expbit0],

    [

      AC_RUN_IFELSE(

        [AC_LANG_SOURCE([[

#include <float.h>

#include <stddef.h>

#include <stdio.h>

#include <string.h>

#define NWORDS \

  ((sizeof (float) + sizeof (unsigned int) - 1) / sizeof (unsigned int))

typedef union { float value; unsigned int word[NWORDS]; } memory_float;

static unsigned int ored_words[NWORDS];

static unsigned int anded_words[NWORDS];

static void add_to_ored_words (float x)

{

  memory_float m;

  size_t i;

  /* Clear it first, in case

     sizeof (float) < sizeof (memory_float).  */

  memset (&m, 0, sizeof (memory_float));

  m.value = x;

  for (i = 0; i < NWORDS; i++)

    {

      ored_words[i] |= m.word[i];

      anded_words[i] &= m.word[i];

    }

}

int main ()

{

  size_t j;

  FILE *fp = fopen ("conftest.out", "w");

  if (fp == NULL)

    return 1;

  for (j = 0; j < NWORDS; j++)

    anded_words[j] = ~ (unsigned int) 0;

  add_to_ored_words (0.25f);

  add_to_ored_words (0.5f);

  add_to_ored_words (1.0f);

  add_to_ored_words (2.0f);

  add_to_ored_words (4.0f);

  /* Remove bits that are common (e.g. if representation of the first mantissa

     bit is explicit).  */

  for (j = 0; j < NWORDS; j++)

    ored_words[j] &= ~anded_words[j];

  /* Now find the nonzero word.  */

  for (j = 0; j < NWORDS; j++)

    if (ored_words[j] != 0)

      break;

  if (j < NWORDS)

    {

      size_t i;

      for (i = j + 1; i < NWORDS; i++)

        if (ored_words[i] != 0)

          {

            fprintf (fp, "unknown");

            return (fclose (fp) != 0);

          }

      for (i = 0; ; i++)

        if ((ored_words[j] >> i) & 1)

          {

            fprintf (fp, "word %d bit %d", (int) j, (int) i);

            return (fclose (fp) != 0);

          }

    }

  fprintf (fp, "unknown");

  return (fclose (fp) != 0);

}

        ]])],

        [gl_cv_cc_float_expbit0=`cat conftest.out`],

        [gl_cv_cc_float_expbit0="unknown"],

        [gl_cv_cc_float_expbit0="word 0 bit 23"])

      rm -f conftest.out

    ])

  case "$gl_cv_cc_float_expbit0" in

    word*bit*)

      word=`echo "$gl_cv_cc_float_expbit0" | sed -e 's/word //' -e 's/ bit.*//'`

      bit=`echo "$gl_cv_cc_float_expbit0" | sed -e 's/word.*bit //'`

      AC_DEFINE_UNQUOTED([FLT_EXPBIT0_WORD], [$word],

        [Define as the word index where to find the exponent of 'float'.])

      AC_DEFINE_UNQUOTED([FLT_EXPBIT0_BIT], [$bit],

        [Define as the bit index in the word where to find bit 0 of the exponent of 'float'.])

      ;;

  esac

])