File: [cvs.NetBSD.org] / src / lib / libm / src / s_scalbn.c (download)
Revision 1.17, Sat Apr 27 18:43:25 2013 UTC (10 years, 11 months ago) by joerg
Branch: MAIN
Changes since 1.16: +2 -1
lines
Add aliases to scalbn* as ldexp*, they are identical for FLT_RADIX=2.
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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.
* ====================================================
*/
#include <sys/cdefs.h>
#if defined(LIBM_SCCS) && !defined(lint)
__RCSID("$NetBSD: s_scalbn.c,v 1.17 2013/04/27 18:43:25 joerg 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 "namespace.h"
#include "math.h"
#include "math_private.h"
#ifndef _LP64
__strong_alias(_scalbn, _scalbln)
#endif
#ifndef __HAVE_LONG_DOUBLE
__strong_alias(_scalbnl, _scalbn)
__strong_alias(_scalblnl, _scalbln)
__weak_alias(scalbnl, _scalbnl)
__weak_alias(scalblnl, _scalblnl)
#endif
#ifdef __weak_alias
__weak_alias(scalbn, _scalbn)
__weak_alias(scalbln, _scalbln)
__weak_alias(ldexp, _scalbln);
#endif
static const double
two54 = 0x1.0p54, /* 0x43500000, 0x00000000 */
twom54 = 0x1.0p-54, /* 0x3C900000, 0x00000000 */
huge = 1.0e+300,
tiny = 1.0e-300;
#ifdef _LP64
double
scalbn(double x, int n)
{
return scalbln(x, n);
}
#endif
double
scalbln(double x, long n)
{
int32_t k,hx,lx;
EXTRACT_WORDS(hx,lx,x);
k = ((uint32_t)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 = (((uint32_t)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;
}