e_sqrtf.c revision 97409 
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: head/lib/msun/src/e_sqrtf.c 97409 2002-05-28 17:51:46Z alfred $";
18#endif
19
20#include "math.h"
21#include "math_private.h"
22
23static	const float	one	= 1.0, tiny=1.0e-30;
24
25	float __ieee754_sqrtf(float x)
26{
27	float z;
28	int32_t sign = (int)0x80000000;
29	int32_t ix,s,q,m,t,i;
30	u_int32_t r;
31
32	GET_FLOAT_WORD(ix,x);
33
34    /* take care of Inf and NaN */
35	if((ix&0x7f800000)==0x7f800000) {
36	    return x*x+x;		/* sqrt(NaN)=NaN, sqrt(+inf)=+inf
37					   sqrt(-inf)=sNaN */
38	}
39    /* take care of zero */
40	if(ix<=0) {
41	    if((ix&(~sign))==0) return x;/* sqrt(+-0) = +-0 */
42	    else if(ix<0)
43		return (x-x)/(x-x);		/* sqrt(-ve) = sNaN */
44	}
45    /* normalize x */
46	m = (ix>>23);
47	if(m==0) {				/* subnormal x */
48	    for(i=0;(ix&0x00800000)==0;i++) ix<<=1;
49	    m -= i-1;
50	}
51	m -= 127;	/* unbias exponent */
52	ix = (ix&0x007fffff)|0x00800000;
53	if(m&1)	/* odd m, double x to make it even */
54	    ix += ix;
55	m >>= 1;	/* m = [m/2] */
56
57    /* generate sqrt(x) bit by bit */
58	ix += ix;
59	q = s = 0;		/* q = sqrt(x) */
60	r = 0x01000000;		/* r = moving bit from right to left */
61
62	while(r!=0) {
63	    t = s+r;
64	    if(t<=ix) {
65		s    = t+r;
66		ix  -= t;
67		q   += r;
68	    }
69	    ix += ix;
70	    r>>=1;
71	}
72
73    /* use floating add to find out rounding direction */
74	if(ix!=0) {
75	    z = one-tiny; /* trigger inexact flag */
76	    if (z>=one) {
77	        z = one+tiny;
78		if (z>one)
79		    q += 2;
80		else
81		    q += (q&1);
82	    }
83	}
84	ix = (q>>1)+0x3f000000;
85	ix += (m <<23);
86	SET_FLOAT_WORD(z,ix);
87	return z;
88}
89