/*
 * 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 __exp2 = exp2

/* INDENT OFF */
/*
 * exp2(x)
 * Code by K.C. Ng for SUN 4.0 libm.
 * Method :
 *      exp2(x) = 2**x = 2**((x-anint(x))+anint(x))
 *              = 2**anint(x)*2**(x-anint(x))
 *              = 2**anint(x)*exp((x-anint(x))*ln2)
 */
/* INDENT ON */

#include "libm.h"

static const double C[] = {
        0.0,
        1.0,
        0.5,
        6.93147180559945286227e-01,
        1.0e300,
        1.0e-300,
};

#define zero    C[0]
#define one     C[1]
#define half    C[2]
#define ln2     C[3]
#define huge    C[4]
#define tiny    C[5]

double
exp2(double x) {
        int     ix, hx, k;
        double  t;

        ix = ((int *)&x)[HIWORD];
        hx = ix & ~0x80000000;

        if (hx >= 0x4090e000) { /* |x| >= 1080 or x is nan */
                if (hx >= 0x7ff00000) { /* x is inf or nan */
                        if (ix == 0xfff00000 && ((int *)&x)[LOWORD] == 0)
                                return (zero);
                        return (x * x);
                }
                t = (ix < 0)? tiny : huge;
                return (t * t);
        }

        if (hx < 0x3fe00000) {  /* |x| < 0.5 */
                if (hx < 0x3c000000)
                        return (one + x);
                return (exp(ln2 * x));
        }

        k = (int)x;
        if (x != (double)k)
                k = (int)((ix < 0)? x - half : x + half);
        return (scalbn(exp(ln2 * (x - (double)k)), k));
}