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58 lines
1.7 KiB
C
58 lines
1.7 KiB
C
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/* @(#)s_scalbn.c 1.3 95/01/18 */
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunSoft, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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/*
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* scalbn (double x, int n)
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* scalbn(x,n) returns x* 2**n computed by exponent
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* manipulation rather than by actually performing an
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* exponentiation or a multiplication.
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*/
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#include "math.h"
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static const double
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two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
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twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
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hugev = 1.0e+300,
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tinyv = 1.0e-300;
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double scalbn(double x, int n) {
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int k, hx, lx;
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hx = __HI(x);
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lx = __LO(x);
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k = (hx & 0x7ff00000) >> 20; /* extract exponent */
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if(k == 0) { /* 0 or subnormal x */
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if((lx | (hx & 0x7fffffff)) == 0) return x; /* +-0 */
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x *= two54;
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hx = __HI(x);
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k = ((hx & 0x7ff00000) >> 20) - 54;
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if(n < -50000) return tinyv * x; /*underflow*/
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}
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if(k == 0x7ff) return x + x; /* NaN or Inf */
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k = k + n;
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if(k > 0x7fe) return hugev * copysign(hugev, x); /* overflow */
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if(k > 0) /* normal result */
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{
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__HI(x) = (hx & 0x800fffff) | (k << 20);
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return x;
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}
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if(k <= -54)
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if(n > 50000) /* in case integer overflow in n+k */
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return hugev * copysign(hugev, x); /*overflow*/
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else
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return tinyv * copysign(tinyv, x); /*underflow*/
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k += 54; /* subnormal result */
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__HI(x) = (hx & 0x800fffff) | (k << 20);
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return x * twom54;
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}
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