gen/common/fmod.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (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 1988 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#pragma ident   "%Z%%M% %I% %E% SMI"

/* Special version adapted from libm for use in libc. */

static int  n0 = 0, n1 = 1;

static double   two52 = 4.503599627370496000E+15;
static double   twom52 = 2.220446049250313081E-16;

static double
setexception(int n, double x)
{
    return (0.0);
}

double
copysign(double x, double y)
{
    long           *px = (long *) &x;
    long           *py = (long *) &y;
    px[n0] = (px[n0] & 0x7fffffff) | (py[n0] & 0x80000000);
    return (x);
}

static double
fabs(double x)
{
    long           *px = (long *) &x;
    px[0] &= 0x7fffffff;

    return (x);
}

static int
finite(double x)
{
    long           *px = (long *) &x;
    return ((px[n0] & 0x7ff00000) != 0x7ff00000);
}

static int
ilogb(double x)
{
    long           *px = (long *) &x, k;
    k = px[n0] & 0x7ff00000;
    if (k == 0) {
        if ((px[n1] | (px[n0] & 0x7fffffff)) == 0)
            return (0x80000001);
        else {
            x *= two52;
            return ((px[n0] & 0x7ff00000) >> 20) - 1075;
        }
    } else if (k != 0x7ff00000)
        return (k >> 20) - 1023;
    else
        return (0x7fffffff);
}

static double
scalbn(double x, int n)
{
    long           *px = (long *) &x, k;
    double          twom54 = twom52 * 0.25;
    k = (px[n0] & 0x7ff00000) >> 20;
    if (k == 0x7ff)
        return (x + x);
    if ((px[n1] | (px[n0] & 0x7fffffff)) == 0)
        return (x);
    if (k == 0) {
        x *= two52;
        k = ((px[n0] & 0x7ff00000) >> 20) - 52;
    }
    k = k + n;
    if (n > 5000)
        return (setexception(2, x));
    if (n < -5000)
        return (setexception(1, x));
    if (k > 0x7fe)
        return (setexception(2, x));
    if (k <= -54)
        return (setexception(1, x));
    if (k > 0) {
        px[n0] = (px[n0] & 0x800fffff) | (k << 20);
        return (x);
    }
    k += 54;
    px[n0] = (px[n0] & 0x800fffff) | (k << 20);
    return (x * twom54);
}

double
fmod(double x, double y)
{
    int             ny, nr;
    double          r, z, w;

    int finite(), ilogb();
    double fabs(), scalbn(), copysign();

    /* purge off exception values */
    if (!finite(x) || y != y || y == 0.0) {
        return ((x * y) / (x * y));
    }
    /* scale and subtract to get the remainder */
    r = fabs(x);
    y = fabs(y);
    ny = ilogb(y);
    while (r >= y) {
        nr = ilogb(r);
        if (nr == ny)
            w = y;
        else {
            z = scalbn(y, nr - ny - 1);
            w = z + z;
        }
        if (r >= w)
            r -= w;
        else
            r -= z;
    }

    /* restore sign */
    return (copysign(r, x));
}