/*
 * 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 nearbyint = __nearbyint

/*
 * nearbyint(x) returns the nearest fp integer to x in the direction
 * corresponding to the current rounding direction without raising
 * the inexact exception.
 *
 * nearbyint(x) is x unchanged if x is +/-0 or +/-inf.  If x is NaN,
 * nearbyint(x) is also NaN.
 */

#include "libm.h"
#include <fenv.h>

double
__nearbyint(double x) {
        union {
                unsigned i[2];
                double d;
        } xx;
        unsigned hx, sx, i, frac;
        int rm, j;

        xx.d = x;
        sx = xx.i[HIWORD] & 0x80000000;
        hx = xx.i[HIWORD] & ~0x80000000;

        /* handle trivial cases */
        if (hx >= 0x43300000) { /* x is nan, inf, or already integral */
                if (hx >= 0x7ff00000)   /* x is inf or nan */
#if defined(FPADD_TRAPS_INCOMPLETE_ON_NAN)
                        return (hx >= 0x7ff80000 ? x : x + x);
                        /* assumes sparc-like QNaN */
#else
                        return (x + x);
#endif
                return (x);
        } else if ((hx | xx.i[LOWORD]) == 0)    /* x is zero */
                return (x);

        /* get the rounding mode */
        rm = fegetround();

        /* flip the sense of directed roundings if x is negative */
        if (sx && (rm == FE_UPWARD || rm == FE_DOWNWARD))
                rm = (FE_UPWARD + FE_DOWNWARD) - rm;

        /* handle |x| < 1 */
        if (hx < 0x3ff00000) {
                if (rm == FE_UPWARD || (rm == FE_TONEAREST &&
                        (hx >= 0x3fe00000 && ((hx & 0xfffff) | xx.i[LOWORD]))))
                        xx.i[HIWORD] = sx | 0x3ff00000;
                else
                        xx.i[HIWORD] = sx;
                xx.i[LOWORD] = 0;
                return (xx.d);
        }

        /* round x at the integer bit */
        j = 0x433 - (hx >> 20);
        if (j >= 32) {
                i = 1 << (j - 32);
                frac = ((xx.i[HIWORD] << 1) << (63 - j)) |
                        (xx.i[LOWORD] >> (j - 32));
                if (xx.i[LOWORD] & (i - 1))
                        frac |= 1;
                if (!frac)
                        return (x);
                xx.i[LOWORD] = 0;
                xx.i[HIWORD] &= ~(i - 1);
                if ((rm == FE_UPWARD) || ((rm == FE_TONEAREST) &&
                        ((frac > 0x80000000u) || ((frac == 0x80000000) &&
                        (xx.i[HIWORD] & i)))))
                        xx.i[HIWORD] += i;
        } else {
                i = 1 << j;
                frac = (xx.i[LOWORD] << 1) << (31 - j);
                if (!frac)
                        return (x);
                xx.i[LOWORD] &= ~(i - 1);
                if ((rm == FE_UPWARD) || ((rm == FE_TONEAREST) &&
                        (frac > 0x80000000u || ((frac == 0x80000000) &&
                        (xx.i[LOWORD] & i))))) {
                        xx.i[LOWORD] += i;
                        if (xx.i[LOWORD] == 0)
                                xx.i[HIWORD]++;
                }
        }
        return (xx.d);
}