xref: /freebsd/lib/msun/src/e_acosf.c (revision 06c3fb27)
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 #include "math.h"
18 #include "math_private.h"
19 
20 static const float
21 one =  1.0000000000e+00, /* 0x3F800000 */
22 pi =  3.1415925026e+00, /* 0x40490fda */
23 pio2_hi =  1.5707962513e+00; /* 0x3fc90fda */
24 static volatile float
25 pio2_lo =  7.5497894159e-08; /* 0x33a22168 */
26 static const float
27 pS0 =  1.6666586697e-01,
28 pS1 = -4.2743422091e-02,
29 pS2 = -8.6563630030e-03,
30 qS1 = -7.0662963390e-01;
31 
32 float
33 acosf(float x)
34 {
35 	float z,p,q,r,w,s,c,df;
36 	int32_t hx,ix;
37 	GET_FLOAT_WORD(hx,x);
38 	ix = hx&0x7fffffff;
39 	if(ix>=0x3f800000) {		/* |x| >= 1 */
40 	    if(ix==0x3f800000) {	/* |x| == 1 */
41 		if(hx>0) return 0.0;	/* acos(1) = 0 */
42 		else return pi+(float)2.0*pio2_lo;	/* acos(-1)= pi */
43 	    }
44 	    return (x-x)/(x-x);		/* acos(|x|>1) is NaN */
45 	}
46 	if(ix<0x3f000000) {	/* |x| < 0.5 */
47 	    if(ix<=0x32800000) return pio2_hi+pio2_lo;/*if|x|<2**-26*/
48 	    z = x*x;
49 	    p = z*(pS0+z*(pS1+z*pS2));
50 	    q = one+z*qS1;
51 	    r = p/q;
52 	    return pio2_hi - (x - (pio2_lo-x*r));
53 	} else  if (hx<0) {		/* x < -0.5 */
54 	    z = (one+x)*(float)0.5;
55 	    p = z*(pS0+z*(pS1+z*pS2));
56 	    q = one+z*qS1;
57 	    s = sqrtf(z);
58 	    r = p/q;
59 	    w = r*s-pio2_lo;
60 	    return pi - (float)2.0*(s+w);
61 	} else {			/* x > 0.5 */
62 	    int32_t idf;
63 	    z = (one-x)*(float)0.5;
64 	    s = sqrtf(z);
65 	    df = s;
66 	    GET_FLOAT_WORD(idf,df);
67 	    SET_FLOAT_WORD(df,idf&0xfffff000);
68 	    c  = (z-df*df)/(s+df);
69 	    p = z*(pS0+z*(pS1+z*pS2));
70 	    q = one+z*qS1;
71 	    r = p/q;
72 	    w = r*s+c;
73 	    return (float)2.0*(df+w);
74 	}
75 }
76