ref: a39ae178fcc4387fe63efea4d15b34d52f4a13de
dir: /libmath/fdlibm/s_scalbn.c/
/* derived from /netlib/fdlibm */
/* @(#)s_scalbn.c 1.3 95/01/18 */
/*
* ====================================================
* 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.
* ====================================================
*/
/*
* 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"
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)
{
int k,hx,lx;
hx = __HI(x);
lx = __LO(x);
k = (hx&0x7ff00000)>>20; /* extract exponent */
if (k==0) { /* 0 or subnormal x */
if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
x *= two54;
hx = __HI(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 */
{__HI(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 */
__HI(x) = (hx&0x800fffff)|(k<<20);
return x*twom54;
}