File: [cvs.NetBSD.org] / src / lib / libm / src / s_scalbn.c (download)
Revision 1.14, Fri Apr 23 19:17:07 2010 UTC (13 years, 11 months ago) by drochner
Branch: MAIN
CVS Tags: matt-mips64-premerge-20101231, cherry-xenmp-base, cherry-xenmp, bouyer-quota2-nbase, bouyer-quota2-base, bouyer-quota2 Changes since 1.13: +6 -1
lines
-build ldexp/frexp/modf locally again rather than relying on libc
reaching over, to get things into a sane state,
-do the usual namespace protection game with scalbn(f) because it
is used internally
(more symbol renamings are necessary)
The weak_alias change for mc68881 is untested.
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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 1.14 2010/04/23 19:17:07 drochner 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"
#ifdef __weak_alias
__weak_alias(scalbn, _scalbn)
#endif
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)
{
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;
}