xref: /freebsd/lib/msun/src/e_acosf.c (revision e0345583223ac3daf6814f9a3efd3d1440b6315e)
1 /* e_acosf.c -- float version of e_acos.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 #include <sys/cdefs.h>
17 __FBSDID("$FreeBSD$");
18 
19 #include "math.h"
20 #include "math_private.h"
21 
22 static const float
23 one =  1.0000000000e+00, /* 0x3F800000 */
24 pi =  3.1415925026e+00, /* 0x40490fda */
25 pio2_hi =  1.5707962513e+00; /* 0x3fc90fda */
26 static volatile float
27 pio2_lo =  7.5497894159e-08; /* 0x33a22168 */
28 static const float
29 pS0 =  1.6666586697e-01,
30 pS1 = -4.2743422091e-02,
31 pS2 = -8.6563630030e-03,
32 qS1 = -7.0662963390e-01;
33 
34 float
35 __ieee754_acosf(float x)
36 {
37 	float z,p,q,r,w,s,c,df;
38 	int32_t hx,ix;
39 	GET_FLOAT_WORD(hx,x);
40 	ix = hx&0x7fffffff;
41 	if(ix>=0x3f800000) {		/* |x| >= 1 */
42 	    if(ix==0x3f800000) {	/* |x| == 1 */
43 		if(hx>0) return 0.0;	/* acos(1) = 0 */
44 		else return pi+(float)2.0*pio2_lo;	/* acos(-1)= pi */
45 	    }
46 	    return (x-x)/(x-x);		/* acos(|x|>1) is NaN */
47 	}
48 	if(ix<0x3f000000) {	/* |x| < 0.5 */
49 	    if(ix<=0x32800000) return pio2_hi+pio2_lo;/*if|x|<2**-26*/
50 	    z = x*x;
51 	    p = z*(pS0+z*(pS1+z*pS2));
52 	    q = one+z*qS1;
53 	    r = p/q;
54 	    return pio2_hi - (x - (pio2_lo-x*r));
55 	} else  if (hx<0) {		/* x < -0.5 */
56 	    z = (one+x)*(float)0.5;
57 	    p = z*(pS0+z*(pS1+z*pS2));
58 	    q = one+z*qS1;
59 	    s = sqrtf(z);
60 	    r = p/q;
61 	    w = r*s-pio2_lo;
62 	    return pi - (float)2.0*(s+w);
63 	} else {			/* x > 0.5 */
64 	    int32_t idf;
65 	    z = (one-x)*(float)0.5;
66 	    s = sqrtf(z);
67 	    df = s;
68 	    GET_FLOAT_WORD(idf,df);
69 	    SET_FLOAT_WORD(df,idf&0xfffff000);
70 	    c  = (z-df*df)/(s+df);
71 	    p = z*(pS0+z*(pS1+z*pS2));
72 	    q = one+z*qS1;
73 	    r = p/q;
74 	    w = r*s+c;
75 	    return (float)2.0*(df+w);
76 	}
77 }
78