/* @(#)s_scalbn.c 1.3 95/01/18 */

/*
 * Copyright (c) 2015-2017 Carsten Sonne Larsen  <cs@innolan.dk>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * The origin source code can be obtained from:
 * http://www.netlib.org/fdlibm/s_scalbn.c
 * 
 */

/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 *
 */

#include "prim.h"
#include "math.h"

/*
 * scalbn (double x, int n)
 * scalbn(x,n) returns x* 2**n  computed by  exponent
 * manipulation rather than by actually performing an
 * exponentiation or a multiplication.
 */

static const double
two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
huge   = 1.0e+300,
tiny   = 1.0e-300;

double scalbn (double x, int n)
{
    sword  k,hx,lx;
    EXTRACT_WORDS(hx,lx,x);
    k = (hx&0x7ff00000)>>20;		/* extract exponent */
    if (k==0) {				/* 0 or subnormal x */
        if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
        x *= two54;
        GET_HIGH_WORD(hx,x);
        k = ((hx&0x7ff00000)>>20) - 54;
        if (n< -50000) return tiny*x; 	/*underflow*/
    }
    if (k==0x7ff) return x+x;		/* NaN or Inf */
    k = k+n;
    if (k >  0x7fe) return huge*copysign(huge,x); /* overflow  */
    if (k > 0) 				/* normal result */
    {
        SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
        return x;
    }
    if (k <= -54) {
        if (n > 50000)  	/* in case integer overflow in n+k */
            return huge*copysign(huge,x);	/*overflow*/
        else return tiny*copysign(tiny,x); 	/*underflow*/
    }
    k += 54;				/* subnormal result */
    SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
    return x*twom54;
}
