Subversion Repositories openrisc_2011-10-31

/* @(#)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.

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

 */

/*

FUNCTION

<<scalbn>>, <<scalbnf>>, <<scalbln>>, <<scalblnf>>--scale by power of FLT_RADIX (=2)

INDEX

        scalbn

INDEX

        scalbnf

INDEX

        scalbln

INDEX

        scalblnf

ANSI_SYNOPSIS

        #include <math.h>

        double scalbn(double <[x]>, int <[n]>);

        float scalbnf(float <[x]>, int <[n]>);

        double scalbln(double <[x]>, long int <[n]>);

        float scalblnf(float <[x]>, long int <[n]>);

DESCRIPTION

The <<scalbn>> and <<scalbln>> functions compute

        @ifnottex

        <[x]> times FLT_RADIX to the power <[n]>.

        @end ifnottex

        @tex

        $x \cdot FLT\_RADIX^n$.

        @end tex

efficiently.  The result is computed by manipulating the exponent, rather than

by actually performing an exponentiation or multiplication.  In this

floating-point implementation FLT_RADIX=2, which makes the <<scalbn>>

functions equivalent to the <<ldexp>> functions.

RETURNS

<[x]> times 2 to the power <[n]>.  A range error may occur.

PORTABILITY

ANSI C, POSIX

SEEALSO

<<ldexp>>

*/

/*

 * 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 "fdlibm.h"

#ifndef _DOUBLE_IS_32BITS

#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;

}

#endif /* _DOUBLE_IS_32BITS */