common/m9x/nexttoward.c

/*
 * 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.
 */

#pragma weak nexttoward = __nexttoward

/*
 * nexttoward(x, y) delivers the next representable number after x
 * in the direction of y.  If x and y are both zero, the result is
 * zero with the same sign as y.  If either x or y is NaN, the result
 * is NaN.
 *
 * If x != y and the result is infinite, overflow is raised; if
 * x != y and the result is subnormal or zero, underflow is raised.
 * (This is wrong, but it's what C99 apparently wants.)
 */

#include "libm.h"

#if defined(__sparc)

static union {
    unsigned i[2];
    double d;
} C[] = {
    0x00100000, 0,
    0x7fe00000, 0,
    0x7fffffff, 0xffffffff
};

#define tiny    C[0].d
#define huge    C[1].d
#define qnan    C[2].d

enum fcc_type {
    fcc_equal = 0,
    fcc_less = 1,
    fcc_greater = 2,
    fcc_unordered = 3
};

#ifdef __sparcv9
#define _Q_cmp  _Qp_cmp
#endif

extern enum fcc_type _Q_cmp(const long double *, const long double *);

double
__nexttoward(double x, long double y) {
    union {
        unsigned i[2];
        double d;
    } xx;
    union {
        unsigned i[4];
        long double q;
    } yy;
    long double lx;
    unsigned hx;
    volatile double dummy;
    enum fcc_type rel;

    /*
     * It would be somewhat more efficient to check for NaN and
     * zero operands before converting x to long double and then
     * to code the comparison in line rather than calling _Q_cmp.
     * However, since this code probably won't get used much,
     * I'm opting in favor of simplicity instead.
     */
    lx = xx.d = x;
    hx = (xx.i[0] & ~0x80000000) | xx.i[1];

    /* check for each of four possible orderings */
    rel = _Q_cmp(&lx, &y);
    if (rel == fcc_unordered)
        return (qnan);

    if (rel == fcc_equal) {
        if (hx == 0) {  /* x is zero; return zero with y's sign */
            yy.q = y;
            xx.i[0] = yy.i[0];
            return (xx.d);
        }
        return (x);
    }

    if (rel == fcc_less) {
        if (hx == 0) {  /* x is zero */
            xx.i[0] = 0;
            xx.i[1] = 0x00000001;
        } else if ((int)xx.i[0] >= 0) { /* x is positive */
            if (++xx.i[1] == 0)
                xx.i[0]++;
        } else {
            if (xx.i[1]-- == 0)
                xx.i[0]--;
        }
    } else {
        if (hx == 0) {  /* x is zero */
            xx.i[0] = 0x80000000;
            xx.i[1] = 0x00000001;
        } else if ((int)xx.i[0] >= 0) { /* x is positive */
            if (xx.i[1]-- == 0)
                xx.i[0]--;
        } else {
            if (++xx.i[1] == 0)
                xx.i[0]++;
        }
    }

    /* raise exceptions as needed */
    hx = xx.i[0] & ~0x80000000;
    if (hx == 0x7ff00000) {
        dummy = huge;
        dummy *= huge;
    } else if (hx < 0x00100000) {
        dummy = tiny;
        dummy *= tiny;
    }

    return (xx.d);
}

#elif defined(__x86)

static union {
    unsigned i[2];
    double d;
} C[] = {
    0, 0x00100000,
    0, 0x7fe00000,
};

#define tiny    C[0].d
#define huge    C[1].d

double
__nexttoward(double x, long double y) {
    union {
        unsigned i[2];
        double d;
    } xx;
    unsigned hx;
    long double lx;
    volatile double dummy;

    lx = xx.d = x;
    hx = (xx.i[1] & ~0x80000000) | xx.i[0];

    /* check for each of four possible orderings */
    if (isunordered(lx, y))
        return ((double) (lx + y));

    if (lx == y)
        return ((double) y);

    if (lx < y) {
        if (hx == 0) {  /* x is zero */
            xx.i[0] = 0x00000001;
            xx.i[1] = 0;
        } else if ((int)xx.i[1] >= 0) { /* x is positive */
            if (++xx.i[0] == 0)
                xx.i[1]++;
        } else {
            if (xx.i[0]-- == 0)
                xx.i[1]--;
        }
    } else {
        if (hx == 0) {  /* x is zero */
            xx.i[0] = 0x00000001;
            xx.i[1] = 0x80000000;
        } else if ((int)xx.i[1] >= 0) { /* x is positive */
            if (xx.i[0]-- == 0)
                xx.i[1]--;
        } else {
            if (++xx.i[0] == 0)
                xx.i[1]++;
        }
    }

    /* raise exceptions as needed */
    hx = xx.i[1] & ~0x80000000;
    if (hx == 0x7ff00000) {
        dummy = huge;
        dummy *= huge;
    } else if (hx < 0x00100000) {
        dummy = tiny;
        dummy *= tiny;
    }

    return (xx.d);
}

#else
#error Unknown architecture
#endif