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s_scalbn.c
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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.
* ====================================================
*/
#if defined(LIBM_SCCS) && !defined(lint)
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static const char rcsid[] =
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"$NetBSD: s_scalbn.c,v 1.8 1995/05/10 20:48:08 jtc 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 "math.h"
#include "math_private.h"
libm_hidden_proto(copysign)
#ifdef __STDC__
static const double
#else
static double
#endif
two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
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huge_val = 1.0e+300, tiny = 1.0e-300;
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libm_hidden_proto(scalbn)
#ifdef __STDC__
double scalbn(double x, int n)
#else
double scalbn(x, n)
double x;
int n;
#endif
{
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 (n < -50000)
return tiny * x; /*underflow */
}
if (k == 0x7ff)
return x + x; /* NaN or Inf */
k = k + n;
if (k > 0x7fe)
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return huge_val * copysign(huge_val, x); /* overflow */
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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 */
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return huge_val * copysign(huge_val, x); /*overflow */
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else
return tiny * copysign(tiny, x); /*underflow */
}
k += 54; /* subnormal result */
SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
return x * twom54;
}
libm_hidden_def(scalbn)