common/Q/logbl.c

	logbl.c revision 25c28e83beb90e7c80452a7c818c5e6f73a07dc8
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
 */
/*
 * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#if defined(ELFOBJ)
#pragma weak logbl = __logbl
#endif

#include "libm.h"
#include "xpg6.h"   /* __xpg6 */
#define _C99SUSv3_logb  _C99SUSv3_logb_subnormal_is_like_ilogb

#if defined(__sparc)
#define ISNORMALL(k, x) (k != 0x7fff)           /* assuming k != 0 */
#define X86PDNRM(k, x)
#define XSCALE_OFFSET   0x406f              /* 0x3fff + 112 */
static const long double xscale = 5192296858534827628530496329220096.0L;
                                /* 2^112 */
#elif defined(__x86)
/*
 * if pseudo-denormal, replace by the equivalent normal
 */
#define X86PDNRM(k, x)  if (k == 0 && (((int *) &x)[1] & 0x80000000) != 0) \
                ((int *) &x)[2] |= k = 1
#if defined(HANDLE_UNSUPPORTED)             /* assuming k != 0 */
#define ISNORMALL(k, x) (k != 0x7fff && (((int *) &x)[1] & 0x80000000) != 0)
#else
#define ISNORMALL(k, x) (k != 0x7fff)
#endif
#define XSCALE_OFFSET   0x403e              /* 0x3fff + 63 */
static const long double xscale = 9223372036854775808.0L;   /* 2^63 */
#endif

static long double
raise_division(long double v) {
#pragma STDC FENV_ACCESS ON
    static const long double zero = 0.0L;
    return (v / zero);
}

long double
logbl(long double x) {
    int k = XBIASED_EXP(x);

    X86PDNRM(k, x);
    if (k == 0) {
        if (ISZEROL(x))
            return (raise_division(-1.0L));
        else if ((__xpg6 & _C99SUSv3_logb) != 0) {
            x *= xscale;        /* scale up by 2^112 or 2^63 */
            return (long double) (XBIASED_EXP(x) - XSCALE_OFFSET);
        } else
            return (-16382.L);
    } else if (ISNORMALL(k, x))
        return ((long double) (k - 0x3fff));
    else
        return (x * x);
}