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[] = "$FreeBSD$";
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 #if defined(LK) && ARCH_ARM && ARM_WITH_VFP
26 /* use ARM w/VFP sqrt instruction */
27 float
__ieee754_sqrtf(float x)28 __ieee754_sqrtf(float x)
29 {
30 float res;
31
32 __asm__("vsqrt.f32 %0, %1" : "=t"(res) : "t"(x));
33
34 return res;
35 }
36
37 #else
38
39 float
__ieee754_sqrtf(float x)40 __ieee754_sqrtf(float x)
41 {
42 float z;
43 int32_t sign = (int)0x80000000;
44 int32_t ix,s,q,m,t,i;
45 u_int32_t r;
46
47 GET_FLOAT_WORD(ix,x);
48
49 /* take care of Inf and NaN */
50 if ((ix&0x7f800000)==0x7f800000) {
51 return x*x+x; /* sqrt(NaN)=NaN, sqrt(+inf)=+inf
52 sqrt(-inf)=sNaN */
53 }
54 /* take care of zero */
55 if (ix<=0) {
56 if ((ix&(~sign))==0) return x; /* sqrt(+-0) = +-0 */
57 else if (ix<0)
58 return (x-x)/(x-x); /* sqrt(-ve) = sNaN */
59 }
60 /* normalize x */
61 m = (ix>>23);
62 if (m==0) { /* subnormal x */
63 for (i=0; (ix&0x00800000)==0; i++) ix<<=1;
64 m -= i-1;
65 }
66 m -= 127; /* unbias exponent */
67 ix = (ix&0x007fffff)|0x00800000;
68 if (m&1) /* odd m, double x to make it even */
69 ix += ix;
70 m >>= 1; /* m = [m/2] */
71
72 /* generate sqrt(x) bit by bit */
73 ix += ix;
74 q = s = 0; /* q = sqrt(x) */
75 r = 0x01000000; /* r = moving bit from right to left */
76
77 while (r!=0) {
78 t = s+r;
79 if (t<=ix) {
80 s = t+r;
81 ix -= t;
82 q += r;
83 }
84 ix += ix;
85 r>>=1;
86 }
87
88 /* use floating add to find out rounding direction */
89 if (ix!=0) {
90 z = one-tiny; /* trigger inexact flag */
91 if (z>=one) {
92 z = one+tiny;
93 if (z>one)
94 q += 2;
95 else
96 q += (q&1);
97 }
98 }
99 ix = (q>>1)+0x3f000000;
100 ix += (m <<23);
101 SET_FLOAT_WORD(z,ix);
102 return z;
103 }
104
105 #endif
106
107