1 /* ef_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 #include "fdlibm.h"
17 
18 #ifdef __STDC__
19 static	const float	one	= 1.0, tiny=1.0e-30;
20 #else
21 static	float	one	= 1.0, tiny=1.0e-30;
22 #endif
23 
24 #ifdef __STDC__
__ieee754_sqrtf(float x)25 	float __ieee754_sqrtf(float x)
26 #else
27 	float __ieee754_sqrtf(x)
28 	float x;
29 #endif
30 {
31 	float z;
32 	__int32_t 	sign = (__int32_t)0x80000000;
33 	__uint32_t r,hx;
34 	__int32_t ix,s,q,m,t,i;
35 
36 	GET_FLOAT_WORD(ix,x);
37 	hx = ix&0x7fffffff;
38 
39     /* take care of Inf and NaN */
40 	if(!FLT_UWORD_IS_FINITE(hx))
41 	    return x*x+x;		/* sqrt(NaN)=NaN, sqrt(+inf)=+inf
42 					   sqrt(-inf)=sNaN */
43     /* take care of zero and -ves */
44 	if(FLT_UWORD_IS_ZERO(hx)) return x;/* sqrt(+-0) = +-0 */
45 	if(ix<0) return (x-x)/(x-x);		/* sqrt(-ve) = sNaN */
46 
47     /* normalize x */
48 	m = (ix>>23);
49 	if(FLT_UWORD_IS_SUBNORMAL(hx)) {		/* subnormal x */
50 	    for(i=0;(ix&0x00800000L)==0;i++) ix<<=1;
51 	    m -= i-1;
52 	}
53 	m -= 127;	/* unbias exponent */
54 	ix = (ix&0x007fffffL)|0x00800000L;
55 	if(m&1)	/* odd m, double x to make it even */
56 	    ix += ix;
57 	m >>= 1;	/* m = [m/2] */
58 
59     /* generate sqrt(x) bit by bit */
60 	ix += ix;
61 	q = s = 0;		/* q = sqrt(x) */
62 	r = 0x01000000L;		/* r = moving bit from right to left */
63 
64 	while(r!=0) {
65 	    t = s+r;
66 	    if(t<=ix) {
67 		s    = t+r;
68 		ix  -= t;
69 		q   += r;
70 	    }
71 	    ix += ix;
72 	    r>>=1;
73 	}
74 
75     /* use floating add to find out rounding direction */
76 	if(ix!=0) {
77 	    z = one-tiny; /* trigger inexact flag */
78 	    if (z>=one) {
79 	        z = one+tiny;
80 		if (z>one)
81 		    q += 2;
82 		else
83 		    q += (q&1);
84 	    }
85 	}
86 	ix = (q>>1)+0x3f000000L;
87 	ix += (m <<23);
88 	SET_FLOAT_WORD(z,ix);
89 	return z;
90 }
91