mirror of
https://sourceware.org/git/glibc.git
synced 2024-12-12 22:30:12 +00:00
61 lines
1.8 KiB
C
61 lines
1.8 KiB
C
/*
|
|
* ====================================================
|
|
* 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.
|
|
* ====================================================
|
|
*/
|
|
|
|
/*
|
|
* 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 <math.h>
|
|
#include <math_private.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)
|
|
{
|
|
int32_t k,hx,lx;
|
|
EXTRACT_WORDS(hx,lx,x);
|
|
k = (hx&0x7ff00000)>>20; /* extract exponent */
|
|
if (__builtin_expect(k==0, 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 (__builtin_expect(k==0x7ff, 0)) return x+x; /* NaN or Inf */
|
|
if (__builtin_expect(n< -50000, 0))
|
|
return tiny*__copysign(tiny,x); /*underflow*/
|
|
if (__builtin_expect(n> 50000 || k+n > 0x7fe, 0))
|
|
return huge*__copysign(huge,x); /* overflow */
|
|
/* Now k and n are bounded we know that k = k+n does not
|
|
overflow. */
|
|
k = k+n;
|
|
if (__builtin_expect(k > 0, 1)) /* normal result */
|
|
{SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
|
|
if (k <= -54)
|
|
return tiny*__copysign(tiny,x); /*underflow*/
|
|
k += 54; /* subnormal result */
|
|
SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
|
|
return x*twom54;
|
|
}
|
|
weak_alias (__scalbn, scalbn)
|
|
#ifdef NO_LONG_DOUBLE
|
|
strong_alias (__scalbn, __scalbnl)
|
|
weak_alias (__scalbn, scalbnl)
|
|
#endif
|