mirror of https://github.com/encounter/SDL.git
80 lines
2.3 KiB
C
80 lines
2.3 KiB
C
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/* @(#)s_scalbn.c 5.1 93/09/24 */
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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 SunPro, 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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#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 $";
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#endif
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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_libm.h"
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#include "math_private.h"
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libm_hidden_proto(copysign)
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#ifdef __STDC__
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static const double
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#else
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static double
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#endif
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two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
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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)
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#ifdef __STDC__
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double scalbn(double x, int n)
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#else
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double scalbn(x, n)
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double x;
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int n;
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#endif
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{
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int32_t k, hx, lx;
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EXTRACT_WORDS(hx, lx, 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)
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return x; /* +-0 */
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x *= two54;
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GET_HIGH_WORD(hx, x);
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k = ((hx & 0x7ff00000) >> 20) - 54;
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if (n < -50000)
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return tiny * x; /* underflow */
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}
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if (k == 0x7ff)
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return x + x; /* NaN or Inf */
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k = k + n;
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if (k > 0x7fe)
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return huge_val * copysign(huge_val, x); /* overflow */
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if (k > 0) { /* normal result */
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SET_HIGH_WORD(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 huge_val * copysign(huge_val, x); /* overflow */
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else
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return tiny * copysign(tiny, x); /* underflow */
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}
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k += 54; /* subnormal result */
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SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
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return x * twom54;
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}
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libm_hidden_def(scalbn)
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