source: trunk/minix/lib/math/sqrt.c@ 15

/*
 * (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: /cvsup/minix/src/lib/math/sqrt.c,v 1.1.1.1 2005/04/21 14:56:26 beng Exp $ */

#include        <math.h>
#include        <float.h>
#include        <errno.h>

#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;
}