e_sqrtf.c revision 2116 
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[] = "$Id: e_sqrtf.c,v 1.2 1994/08/18 23:06:07 jtc Exp $";
18#endif
19
20#include "math.h"
21#include "math_private.h"
22
23#ifdef __STDC__
24static	const float	one	= 1.0, tiny=1.0e-30;
25#else
26static	float	one	= 1.0, tiny=1.0e-30;
27#endif
28
29#ifdef __STDC__
30	float __ieee754_sqrtf(float x)
31#else
32	float __ieee754_sqrtf(x)
33	float x;
34#endif
35{
36	float z;
37	int32_t sign = (int)0x80000000;
38	int32_t ix,s,q,m,t,i;
39	u_int32_t r;
40
41	GET_FLOAT_WORD(ix,x);
42
43    /* take care of Inf and NaN */
44	if((ix&0x7f800000)==0x7f800000) {
45	    return x*x+x;		/* sqrt(NaN)=NaN, sqrt(+inf)=+inf
46					   sqrt(-inf)=sNaN */
47	}
48    /* take care of zero */
49	if(ix<=0) {
50	    if((ix&(~sign))==0) return x;/* sqrt(+-0) = +-0 */
51	    else if(ix<0)
52		return (x-x)/(x-x);		/* sqrt(-ve) = sNaN */
53	}
54    /* normalize x */
55	m = (ix>>23);
56	if(m==0) {				/* subnormal x */
57	    for(i=0;(ix&0x00800000)==0;i++) ix<<=1;
58	    m -= i-1;
59	}
60	m -= 127;	/* unbias exponent */
61	ix = (ix&0x007fffff)|0x00800000;
62	if(m&1)	/* odd m, double x to make it even */
63	    ix += ix;
64	m >>= 1;	/* m = [m/2] */
65
66    /* generate sqrt(x) bit by bit */
67	ix += ix;
68	q = s = 0;		/* q = sqrt(x) */
69	r = 0x01000000;		/* r = moving bit from right to left */
70
71	while(r!=0) {
72	    t = s+r;
73	    if(t<=ix) {
74		s    = t+r;
75		ix  -= t;
76		q   += r;
77	    }
78	    ix += ix;
79	    r>>=1;
80	}
81
82    /* use floating add to find out rounding direction */
83	if(ix!=0) {
84	    z = one-tiny; /* trigger inexact flag */
85	    if (z>=one) {
86	        z = one+tiny;
87		if (z>one)
88		    q += 2;
89		else
90		    q += (q&1);
91	    }
92	}
93	ix = (q>>1)+0x3f000000;
94	ix += (m <<23);
95	SET_FLOAT_WORD(z,ix);
96	return z;
97}
98