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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.
* ====================================================
*/
/*
FUNCTION
<<scalbn>>, <<scalbnf>>---scale by power of two
INDEX
scalbn
INDEX
scalbnf
ANSI_SYNOPSIS
#include <math.h>
double scalbn(double <[x]>, int <[y]>);
float scalbnf(float <[x]>, int <[y]>);
TRAD_SYNOPSIS
#include <math.h>
double scalbn(<[x]>,<[y]>)
double <[x]>;
int <[y]>;
float scalbnf(<[x]>,<[y]>)
float <[x]>;
int <[y]>;
DESCRIPTION
<<scalbn>> and <<scalbnf>> scale <[x]> by <[n]>, returning <[x]> times
2 to the power <[n]>. The result is computed by manipulating the
exponent, rather than by actually performing an exponentiation or
multiplication.
RETURNS
<[x]> times 2 to the power <[n]>.
PORTABILITY
Neither <<scalbn>> nor <<scalbnf>> is required by ANSI C or by the System V
Interface Definition (Issue 2).
*/
/*
* 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 */
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