s_scalbn.c revision 6b15695578f07a3f72c4c9475c1a261a3021472a
/* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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* The Original Code is Mozilla Communicator client code, released
* March 31, 1998.
*
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* Portions created by the Initial Developer are Copyright (C) 1998
* the Initial Developer. All Rights Reserved.
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/* @(#)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"
#ifdef __STDC__
static const double
#else
static double
#endif
two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
really_big = 1.0e+300,
tiny = 1.0e-300;
#ifdef __STDC__
double fd_scalbn (double x, int n)
#else
double fd_scalbn (x,n)
double x; int n;
#endif
{
fd_twoints u;
int k,hx,lx;
u.d = x;
hx = __HI(u);
lx = __LO(u);
k = (hx&0x7ff00000)>>20; /* extract exponent */
if (k==0) { /* 0 or subnormal x */
if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
x *= two54;
u.d = x;
hx = __HI(u);
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 really_big*fd_copysign(really_big,x); /* overflow */
if (k > 0) /* normal result */
{u.d = x; __HI(u) = (hx&0x800fffff)|(k<<20); x = u.d; return x;}
if (k <= -54) {
if (n > 50000) /* in case integer overflow in n+k */
return really_big*fd_copysign(really_big,x); /*overflow*/
else return tiny*fd_copysign(tiny,x); /*underflow*/
}
k += 54; /* subnormal result */
u.d = x;
__HI(u) = (hx&0x800fffff)|(k<<20);
x = u.d;
return x*twom54;
}