libm/src/s_nan.c

/*-
 * Copyright (c) 2007 David Schultz
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * $FreeBSD$
 */

#include <sys/endian.h>
#include <ctype.h>
#include <float.h>
#include <math.h>
#include <stdint.h>
#include <strings.h>

#include "math_private.h"

/* digittoint is in the FreeBSD C library, but not Bionic at this point */
static int
digittoint(char ch)
{
    int d;

    d = ch - '0';
    if ((unsigned)d < 10) {
        return d;
    }
    d = ch - 'a';
    if ((unsigned)d < 6) {
        return d + 10;
    }
    d = ch - 'A';
    if ((unsigned)d < 6) {
        return d + 10;
    }
    return -1;
}

/*
 * Scan a string of hexadecimal digits (the format nan(3) expects) and
 * make a bit array (using the local endianness). We stop when we
 * encounter an invalid character, NUL, etc.  If we overflow, we do
 * the same as gcc's __builtin_nan(), namely, discard the high order bits.
 *
 * The format this routine accepts needs to be compatible with what is used
 * in contrib/gdtoa/hexnan.c (for strtod/scanf) and what is used in
 * __builtin_nan(). In fact, we're only 100% compatible for strings we
 * consider valid, so we might be violating the C standard. But it's
 * impossible to use nan(3) portably anyway, so this seems good enough.
 */
void
_scan_nan(uint32_t *words, int num_words, const char *s)
{
	int si;		/* index into s */
	int bitpos;	/* index into words (in bits) */

	bzero(words, num_words * sizeof(uint32_t));

	/* Allow a leading '0x'. (It's expected, but redundant.) */
	if (s[0] == '0' && (s[1] == 'x' || s[1] == 'X'))
		s += 2;

	/* Scan forwards in the string, looking for the end of the sequence. */
	for (si = 0; isxdigit(s[si]); si++)
		;

	/* Scan backwards, filling in the bits in words[] as we go. */
#if _BYTE_ORDER == _LITTLE_ENDIAN
	for (bitpos = 0; bitpos < 32 * num_words; bitpos += 4) {
#else
	for (bitpos = 32 * num_words - 4; bitpos >= 0; bitpos -= 4) {
#endif
		if (--si < 0)
			break;
		words[bitpos / 32] |= digittoint(s[si]) << (bitpos % 32);
	}
}

double
nan(const char *s)
{
	union {
		double d;
		uint32_t bits[2];
	} u;

	_scan_nan(u.bits, 2, s);
#if _BYTE_ORDER == _LITTLE_ENDIAN
	u.bits[1] |= 0x7ff80000;
#else
	u.bits[0] |= 0x7ff80000;
#endif
	return (u.d);
}

float
nanf(const char *s)
{
	union {
		float f;
		uint32_t bits[1];
	} u;

	_scan_nan(u.bits, 1, s);
	u.bits[0] |= 0x7fc00000;
	return (u.f);
}

#if (LDBL_MANT_DIG == 53)
__weak_alias(nanl, nan);
#endif