43 lines
786 B
C
43 lines
786 B
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 <float.h>
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#include <errno.h>
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#define NITER 5
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double
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sqrt(double x)
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{
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int exponent;
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double val;
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if (__IsNan(x)) {
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errno = EDOM;
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return x;
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}
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if (x <= 0) {
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if (x < 0) errno = EDOM;
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return 0;
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}
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if (x > DBL_MAX) return x; /* for infinity */
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val = frexp(x, &exponent);
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if (exponent & 1) {
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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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val = (val + x / val) / 2.0;
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}
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return val;
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}
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