minix/lib/math/sqrt.c

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2005-04-21 16:53:53 +02:00
/*
* (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
* See the copyright notice in the ACK home directory, in the file "Copyright".
*
* Author: Ceriel J.H. Jacobs
*/
/* $Header$ */
#include <math.h>
#include <float.h>
#include <errno.h>
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#include "localmath.h"
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#define NITER 5
double
sqrt(double x)
{
int exponent;
double val;
if (__IsNan(x)) {
errno = EDOM;
return x;
}
if (x <= 0) {
if (x < 0) errno = EDOM;
return 0;
}
if (x > DBL_MAX) return x; /* for infinity */
val = frexp(x, &exponent);
if (exponent & 1) {
exponent--;
val *= 2;
}
val = ldexp(val + 1.0, exponent/2 - 1);
/* was: val = (val + 1.0)/2.0; val = ldexp(val, exponent/2); */
for (exponent = NITER - 1; exponent >= 0; exponent--) {
val = (val + x / val) / 2.0;
}
return val;
}