1 /* origin: FreeBSD /usr/src/lib/msun/src/e_acosf.c */
2 /*
3 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
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 "libm.h"
17
18 static const float
19 pio2_hi = 1.5707962513e+00, /* 0x3fc90fda */
20 pio2_lo = 7.5497894159e-08, /* 0x33a22168 */
21 pS0 = 1.6666586697e-01,
22 pS1 = -4.2743422091e-02,
23 pS2 = -8.6563630030e-03,
24 qS1 = -7.0662963390e-01;
25
R(float z)26 static float R(float z)
27 {
28 float_t p, q;
29 p = z*(pS0+z*(pS1+z*pS2));
30 q = 1.0f+z*qS1;
31 return p/q;
32 }
33
acosf(float x)34 float acosf(float x)
35 {
36 float z,w,s,c,df;
37 uint32_t hx,ix;
38
39 GET_FLOAT_WORD(hx, x);
40 ix = hx & 0x7fffffff;
41 /* |x| >= 1 or nan */
42 if (ix >= 0x3f800000) {
43 if (ix == 0x3f800000) {
44 if (hx >> 31)
45 return 2*pio2_hi + 0x1p-120f;
46 return 0;
47 }
48 return 0/(x-x);
49 }
50 /* |x| < 0.5 */
51 if (ix < 0x3f000000) {
52 if (ix <= 0x32800000) /* |x| < 2**-26 */
53 return pio2_hi + 0x1p-120f;
54 return pio2_hi - (x - (pio2_lo-x*R(x*x)));
55 }
56 /* x < -0.5 */
57 if (hx >> 31) {
58 z = (1+x)*0.5f;
59 s = sqrtf(z);
60 w = R(z)*s-pio2_lo;
61 return 2*(pio2_hi - (s+w));
62 }
63 /* x > 0.5 */
64 z = (1-x)*0.5f;
65 s = sqrtf(z);
66 GET_FLOAT_WORD(hx,s);
67 SET_FLOAT_WORD(df,hx&0xfffff000);
68 c = (z-df*df)/(s+df);
69 w = R(z)*s+c;
70 return 2*(df+w);
71 }
72