mirror of https://gitlab.com/rnger/amath
92 lines
3.3 KiB
C
92 lines
3.3 KiB
C
/*-
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* Copyright (c) 2014-2017 Carsten Sonne Larsen <cs@innolan.net>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* Project homepage:
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* https://amath.innolan.net
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*
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* The original source code can be obtained from:
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* http://www.netlib.org/fdlibm/s_scalbn.c
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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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#include "prim.h"
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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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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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huge = 1.0e+300,
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tiny = 1.0e-300;
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double scalbn(double x, int32_t n)
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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)
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{ /* 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 * copysign(huge, x); /* overflow */
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if (k > 0) /* normal result */
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{
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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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{
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if (n > 50000) /* in case integer overflow in n+k */
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return huge * copysign(huge, 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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