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
18static const float
19pio2_hi = 1.5707962513e+00, /* 0x3fc90fda */
20pio2_lo = 7.5497894159e-08, /* 0x33a22168 */
21pS0 =  1.6666586697e-01,
22pS1 = -4.2743422091e-02,
23pS2 = -8.6563630030e-03,
24qS1 = -7.0662963390e-01;
25
26static 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
34float 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