1/* e_sqrtf.c -- float version of e_sqrt.c.
2 */
3
4/*
5 * ====================================================
6 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
7 *
8 * Developed at SunPro, a Sun Microsystems, Inc. business.
9 * Permission to use, copy, modify, and distribute this
10 * software is freely granted, provided that this notice
11 * is preserved.
12 * ====================================================
13 */
14
15#include <math.h>
16#include <math_private.h>
17#include <libm-alias-finite.h>
18#include <math-use-builtins.h>
19
20float
21__ieee754_sqrtf(float x)
22{
23#if USE_SQRTF_BUILTIN
24 return __builtin_sqrtf (x);
25#else
26 /* Use generic implementation. */
27 float z;
28 int32_t sign = (int)0x80000000;
29 int32_t ix,s,q,m,t,i;
30 uint32_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 = 0x1p0 - 0x1.4484cp-100; /* trigger inexact flag. */
76 if (z >= 0x1p0) {
77 z = 0x1p0 + 0x1.4484cp-100;
78 if (z > 0x1p0)
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#endif /* ! USE_SQRTF_BUILTIN */
89}
90#ifndef __ieee754_sqrtf
91libm_alias_finite (__ieee754_sqrtf, __sqrtf)
92#endif
93

source code of glibc/sysdeps/ieee754/flt-32/e_sqrtf.c