74 lines
1.1 KiB
C
74 lines
1.1 KiB
C
/*
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* (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
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* See the copyright notice in the ACK home directory, in the file "Copyright".
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*
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* Author: Ceriel J.H. Jacobs
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*/
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/* $Id$ */
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#define __NO_DEFS
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#include <math.h>
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#include "pc.h"
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#define NITER 5
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static double Ldexp(double fl, int exp)
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{
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int sign = 1;
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int currexp;
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if (fl < 0)
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{
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fl = -fl;
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sign = -1;
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}
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fl = _fef(fl, &currexp);
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exp += currexp;
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if (exp > 0)
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{
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while (exp > 30)
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{
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fl *= (double)(1L << 30);
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exp -= 30;
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}
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fl *= (double)(1L << exp);
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}
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else
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{
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while (exp < -30)
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{
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fl /= (double)(1L << 30);
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exp += 30;
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}
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fl /= (double)(1L << -exp);
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}
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return sign * fl;
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}
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double _sqt(double x)
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{
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int exponent;
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double val;
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if (x <= 0)
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{
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if (x < 0)
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_trp(ESQT);
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return 0;
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}
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val = _fef(x, &exponent);
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if (exponent & 1)
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{
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exponent--;
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val *= 2;
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}
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val = Ldexp(val + 1.0, exponent / 2 - 1);
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/* was: val = (val + 1.0)/2.0; val = Ldexp(val, exponent/2); */
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for (exponent = NITER - 1; exponent >= 0; exponent--)
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{
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val = (val + x / val) / 2.0;
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}
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return val;
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}
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