Hi,
A printf substitute should be able to print numbers in hexadecimal notation
(conversion 'a' or 'A'), and for this is needs to test whether a number is
NaN. The 'x == x' trick doesn't do it, because - as far as I know - this
can trap if x is a signalling NaN. So we need an isnan() function. But
isnan() is available in libm on many systems (AIX, Cygwin, HP-UX, OSF/1,
Solaris), and our users don't want to add a $(PRINTF_LIBM) variable to the
*_LDFLAGS of each of their programs. We can only use it for printf if it
is in libc.
This does it, with a few (hopefully reasonable) assumptions on the
representation of 'double'.
2007-02-24 Bruno Haible <[EMAIL PROTECTED]>
* modules/isnan-nolibm: New file.
* lib/isnan.h: New file.
* lib/isnan.c: New file.
* m4/isnan.m4: New file.
=========================== modules/isnan-nolibm ==============================
Description:
isnan() function: test for NaN, without requiring libm.
Files:
lib/isnan.h
lib/isnan.c
m4/isnan.m4
Depends-on:
configure.ac:
gl_FUNC_ISNAN_NO_LIBM
Makefile.am:
Include:
#include "isnan.h"
License:
LGPL
Maintainer:
Bruno Haible
============================= lib/isnan.h =====================================
/* Test for NaN that does not need libm.
Copyright (C) 2007 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation,
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
#if HAVE_ISNAN_IN_LIBC
/* Get declaration of isnan. */
# include <math.h>
#else
/* Test whether X is a NaN. */
# undef isnan
# define isnan rpl_isnan
extern int isnan (double x);
#endif
============================= lib/isnan.c =====================================
/* Test for NaN that does not need libm.
Copyright (C) 2007 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation,
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
/* Written by Bruno Haible <[EMAIL PROTECTED]>, 2007. */
#include <config.h>
#include <float.h>
#include <string.h>
#define DBL_EXP_MASK ((DBL_MAX_EXP - DBL_MIN_EXP) | 7)
#define NWORDS \
((sizeof (double) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
typedef union { double value; unsigned int word[NWORDS]; } memory_double;
int
rpl_isnan (double x)
{
#if defined DBL_EXPBIT0_WORD && defined DBL_EXPBIT0_BIT
/* Be careful to not do any floating-point operation on x, such as x == x,
because x may be a signaling NaN. */
static memory_double nan = { 0.0 / 0.0 };
static double plus_inf = 1.0 / 0.0;
static double minus_inf = -1.0 / 0.0;
memory_double m;
/* A NaN can be recognized through its exponent. But exclude +Infinity and
-Infinity, which have the same exponent. */
m.value = x;
if ((((m.word[DBL_EXPBIT0_WORD] >> DBL_EXPBIT0_BIT)
^ (nan.word[DBL_EXPBIT0_WORD] >> DBL_EXPBIT0_BIT))
& DBL_EXP_MASK)
== 0)
return (memcmp (&m.value, &plus_inf, sizeof (double)) != 0
&& memcmp (&m.value, &minus_inf, sizeof (double)) != 0);
else
return 0;
#else
/* The configuration did not find sufficient information. Give up about
the signaling NaNs, handle only the quiet NaNs. */
if (x == x)
return 0;
else
return 1;
#endif
}
============================= m4/isnan.m4 =====================================
# isnan.m4 serial 1
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.
dnl Check how to get or define isnan() without linking with libm.
AC_DEFUN([gl_FUNC_ISNAN_NO_LIBM],
[
AC_CHECK_FUNC([isnan],
[gl_cv_func_isnan_no_libm=yes],
[gl_cv_func_isnan_no_libm=no])
if test $gl_cv_func_isnan_no_libm = yes; then
AC_DEFINE([HAVE_ISNAN_IN_LIBC], 1,
[Define if the isnan() function is available in libc.])
else
AC_LIBOBJ([isnan])
gl_DOUBLE_EXPONENT_LOCATION
fi
])
AC_DEFUN([gl_DOUBLE_EXPONENT_LOCATION],
[
AC_CACHE_CHECK([where to find the exponent in a 'double'],
[gl_cv_cc_double_expbit0],
[
AC_TRY_RUN([
#include <float.h>
#include <stddef.h>
#include <stdio.h>
#include <string.h>
#define NWORDS \
((sizeof (double) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
typedef union { double value; unsigned int word[NWORDS]; } memory_double;
static unsigned int ored_words[NWORDS];
static unsigned int anded_words[NWORDS];
static void add_to_ored_words (double x)
{
memory_double m;
size_t i;
/* Clear it first, in case sizeof (double) < sizeof (memory_double). */
memset (&m, 0, sizeof (memory_double));
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 (0.25);
add_to_ored_words (0.5);
add_to_ored_words (1.0);
add_to_ored_words (2.0);
add_to_ored_words (4.0);
/* 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_double_expbit0=`cat conftest.out`],
[gl_cv_cc_double_expbit0="unknown"],
[
dnl On ARM, integer types are stored in little-endian byte order,
dnl but floats are stored in big-endian word order.
AC_EGREP_CPP([mixed_endianness], [
#if defined arm || defined __arm || defined __arm__
mixed_endianness
#endif
],
[gl_cv_cc_double_expbit0="word 0 bit 20"],
[
AC_C_BIGENDIAN(
[gl_cv_cc_double_expbit0="word 0 bit 20"],
[gl_cv_cc_double_expbit0="word 1 bit 20"],
[gl_cv_cc_double_expbit0="unknown"])
])
])
rm -f conftest.out
])
case "$gl_cv_cc_double_expbit0" in
word*bit*)
word=`echo "$gl_cv_cc_double_expbit0" | sed -e 's/word //' -e 's/
bit.*//'`
bit=`echo "$gl_cv_cc_double_expbit0" | sed -e 's/word.*bit //'`
AC_DEFINE_UNQUOTED([DBL_EXPBIT0_WORD], [$word],
[Define as the word index where to find the exponent of 'double'.])
AC_DEFINE_UNQUOTED([DBL_EXPBIT0_BIT], [$bit],
[Define as the bit index in the word where to find bit 0 of the
exponent of 'double'.])
;;
esac
])
