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s_scalbn.c
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/
s_scalbn.c
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/*
* ====================================================
* 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.
* ====================================================
*/
/*
* scalbln(double x, long n)
* scalbln(x,n) returns x * 2**n computed by exponent
* manipulation rather than by actually performing an
* exponentiation or a multiplication.
*/
#include "math_libm.h"
#include "math_private.h"
#include <limits.h>
#ifdef __WATCOMC__ /* Watcom defines huge=__huge */
#undef huge
#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 scalbln(double x, long n)
{
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)
return x; /* +-0 */
x *= two54;
GET_HIGH_WORD(hx, x);
k = ((hx & 0x7ff00000) >> 20) - 54;
}
if (k == 0x7ff)
return x + x; /* NaN or Inf */
k = k + n;
if (k > 0x7fe)
return huge * copysign(huge, x); /* overflow */
if (n < -50000)
return tiny * copysign(tiny, x); /* underflow */
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;
}
libm_hidden_def(scalbln)
double scalbn(double x, int n)
{
return scalbln(x, n);
}
libm_hidden_def(scalbn)