1/* e_sqrtf.c -- float version of e_sqrt.c.
2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
3 */
4
5/*
6 * ====================================================
7 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
8 *
9 * Developed at SunPro, a Sun Microsystems, Inc. business.
10 * Permission to use, copy, modify, and distribute this
11 * software is freely granted, provided that this notice
12 * is preserved.
13 * ====================================================
14 */
15
16#ifndef lint
17static char rcsid[] = "$FreeBSD$";
18#endif
19
20#include "math.h"
21#include "math_private.h"
22
23static	const float	one	= 1.0, tiny=1.0e-30;
24
25float
26__ieee754_sqrtf(float x)
27{
28	float z;
29	int32_t sign = (int)0x80000000;
30	int32_t ix,s,q,m,t,i;
31	u_int32_t r;
32
33	GET_FLOAT_WORD(ix,x);
34
35    /* take care of Inf and NaN */
36	if((ix&0x7f800000)==0x7f800000) {
37	    return x*x+x;		/* sqrt(NaN)=NaN, sqrt(+inf)=+inf
38					   sqrt(-inf)=sNaN */
39	}
40    /* take care of zero */
41	if(ix<=0) {
42	    if((ix&(~sign))==0) return x;/* sqrt(+-0) = +-0 */
43	    else if(ix<0)
44		return (x-x)/(x-x);		/* sqrt(-ve) = sNaN */
45	}
46    /* normalize x */
47	m = (ix>>23);
48	if(m==0) {				/* subnormal x */
49	    for(i=0;(ix&0x00800000)==0;i++) ix<<=1;
50	    m -= i-1;
51	}
52	m -= 127;	/* unbias exponent */
53	ix = (ix&0x007fffff)|0x00800000;
54	if(m&1)	/* odd m, double x to make it even */
55	    ix += ix;
56	m >>= 1;	/* m = [m/2] */
57
58    /* generate sqrt(x) bit by bit */
59	ix += ix;
60	q = s = 0;		/* q = sqrt(x) */
61	r = 0x01000000;		/* r = moving bit from right to left */
62
63	while(r!=0) {
64	    t = s+r;
65	    if(t<=ix) {
66		s    = t+r;
67		ix  -= t;
68		q   += r;
69	    }
70	    ix += ix;
71	    r>>=1;
72	}
73
74    /* use floating add to find out rounding direction */
75	if(ix!=0) {
76	    z = one-tiny; /* trigger inexact flag */
77	    if (z>=one) {
78	        z = one+tiny;
79		if (z>one)
80		    q += 2;
81		else
82		    q += (q&1);
83	    }
84	}
85	ix = (q>>1)+0x3f000000;
86	ix += (m <<23);
87	SET_FLOAT_WORD(z,ix);
88	return z;
89}
90