/*
 * 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