/* origin: FreeBSD /usr/src/lib/msun/src/s_scalbn.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 "libm.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)
{
// FIXME: k+n check depends on signed int overflow.. use unsigned hx
// TODO: when long != int:
// scalbln(x,long n) { if(n>9999)n=9999; else if(n<-9999)n=-9999; return scalbn(x,n); }
// TODO: n < -50000 ...
int32_t k,hx,lx;
EXTRACT_WORDS(hx, lx, x);
k = (hx&0x7ff00000)>>20; /* extract exponent */
if (k == 0) { /* 0 or subnormal x */
if ((lx|(hx&0x7fffffff)) == 0) /* +-0 */
return x;
x *= two54;
GET_HIGH_WORD(hx, x);
k = ((hx&0x7ff00000)>>20) - 54;
if (n < -50000)
return tiny*x; /*underflow*/
}
if (k == 0x7ff) /* NaN or Inf */
return x + x;
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*/
return tiny*copysign(tiny, x); /*underflow*/
k += 54; /* subnormal result */
SET_HIGH_WORD(x, (hx&0x800fffff)|(k<<20));
return x*twom54;
}
