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