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/* @(#)s_scalbn.c 5.1 93/09/24 */

/*

 * ====================================================

 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.

 *

 * Developed at SunPro, a Sun Microsystems, Inc. business.

 * Permission to use, copy, modify, and distribute this

 * software is freely granted, provided that this notice

 * is preserved.

 * ====================================================

 */

#if defined(LIBM_SCCS) && !defined(lint)

static char rcsid[] = "$NetBSD: s_scalbn.c,v 1.8 1995/05/10 20:48:08 jtc Exp $";

#endif

/*

 * 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.

 */

#include "math.h"

#include "math_private.h"

#ifdef __STDC__

static const double

#else

static double

#endif

two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */

twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */

huge   = 1.0e+300,

tiny   = 1.0e-300;

#ifdef __STDC__

        double scalbn (double x, int n)

#else

        double scalbn (x,n)

        double x; int n;

#endif

{

        int32_t 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;

}