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---
e_sqrtf.c (2023B)
---
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
17 static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_sqrtf.c,v 1.7 2002/05/28 18:15:04 alfred Exp $";
18 #endif
19
20 #include "math.h"
21 #include "math_private.h"
22
23 static const float one = 1.0, tiny=1.0e-30;
24
25 float
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 }