56 lines
1.1 KiB
C
56 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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/* $Header$ */
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#include <math.h>
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#include <errno.h>
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extern int errno;
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double
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log(x)
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double x;
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{
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/* log(x) = z*P(z*z)/Q(z*z), z = (x-1)/(x+1), x in [1/sqrt(2), sqrt(2)]
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*/
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/* Hart & Cheney #2707 */
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static double p[5] = {
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0.7504094990777122217455611007e+02,
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-0.1345669115050430235318253537e+03,
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0.7413719213248602512779336470e+02,
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-0.1277249755012330819984385000e+02,
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0.3327108381087686938144000000e+00
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};
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static double q[5] = {
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0.3752047495388561108727775374e+02,
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-0.7979028073715004879439951583e+02,
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0.5616126132118257292058560360e+02,
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-0.1450868091858082685362325000e+02,
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0.1000000000000000000000000000e+01
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};
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extern double frexp();
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double z, zsqr;
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int exponent;
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if (x <= 0) {
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errno = EDOM;
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return 0;
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}
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x = frexp(x, &exponent);
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while (x < M_1_SQRT2) {
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x += x;
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exponent--;
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}
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z = (x-1)/(x+1);
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zsqr = z*z;
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return z * POLYNOM4(zsqr, p) / POLYNOM4(zsqr, q) + exponent * M_LN2;
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}
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