# frexp.m4 serial 3
dnl Copyright (C) 2007 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_FUNC_FREXP],
[
  AC_REQUIRE([gl_MATH_H_DEFAULTS])
  FREXP_LIBM=
  AC_CACHE_CHECK([whether frexp() can be used without linking with libm],
    [gl_cv_func_frexp_no_libm],
    [
      AC_TRY_LINK([#include <math.h>
                   double x;],
                  [int e; return frexp (x, &e) > 0;],
        [gl_cv_func_frexp_no_libm=yes],
        [gl_cv_func_frexp_no_libm=no])
    ])
  if test $gl_cv_func_frexp_no_libm = no; then
    AC_CACHE_CHECK([whether frexp() can be used with libm],
      [gl_cv_func_frexp_in_libm],
      [
        save_LIBS="$LIBS"
        LIBS="$LIBS -lm"
        AC_TRY_LINK([#include <math.h>
                     double x;],
                    [int e; return frexp (x, &e) > 0;],
          [gl_cv_func_frexp_in_libm=yes],
          [gl_cv_func_frexp_in_libm=no])
        LIBS="$save_LIBS"
      ])
    if test $gl_cv_func_frexp_in_libm = yes; then
      FREXP_LIBM=-lm
    fi
  fi
  if test $gl_cv_func_frexp_no_libm = yes \
     || test $gl_cv_func_frexp_in_libm = yes; then
    save_LIBS="$LIBS"
    LIBS="$LIBS $FREXP_LIBM"
    gl_FUNC_FREXP_WORKS
    LIBS="$save_LIBS"
    case "$gl_cv_func_frexp_works" in
      *yes) gl_func_frexp=yes ;;
      *)    gl_func_frexp=no; REPLACE_FREXP=1; FREXP_LIBM= ;;
    esac
  else
    gl_func_frexp=no
  fi
  if test $gl_func_frexp = yes; then
    AC_DEFINE([HAVE_FREXP], 1,
      [Define if the frexp() function is available and works.])
  else
    AC_LIBOBJ([frexp])
  fi
  AC_SUBST([FREXP_LIBM])
])

dnl Test whether frexp() works also on denormalized numbers (this fails e.g. on
dnl NetBSD 3.0) and on infinite numbers (this fails e.g. on IRIX 6.5).
AC_DEFUN([gl_FUNC_FREXP_WORKS],
[
  AC_REQUIRE([AC_PROG_CC])
  AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
  AC_CACHE_CHECK([whether frexp works], [gl_cv_func_frexp_works],
    [
      AC_TRY_RUN([
#include <float.h>
#include <math.h>
int main()
{
  int i;
  volatile double x;
  /* Test on denormalized numbers.  */
  for (i = 1, x = 1.0; i >= DBL_MIN_EXP; i--, x *= 0.5)
    ;
  if (x > 0.0)
    {
      int exp;
      double y = frexp (x, &exp);
      /* On machines with IEEE754 arithmetic: x = 1.11254e-308, exp = -1022.
         On NetBSD: y = 0.75. Correct: y = 0.5.  */
      if (y != 0.5)
        return 1;
    }
  /* Test on infinite numbers.  */
  x = 1.0 / 0.0;
  {
    int exp;
    double y = frexp (x, &exp);
    if (y != x)
      return 1;
  }
  return 0;
}], [gl_cv_func_frexp_works=yes], [gl_cv_func_frexp_works=no],
      [case "$host_os" in
         netbsd* | irix*) gl_cv_func_frexp_works="guessing no";;
         *)               gl_cv_func_frexp_works="guessing yes";;
       esac
      ])
    ])
])