/* @(#)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"

libm_hidden_proto(copysign)

#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;

libm_hidden_proto(scalbn)

#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;

}

libm_hidden_def(scalbn)