1 /* e_asinf.c -- float version of e_asin.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 "math.h"
17 #include "math_private.h"
18
19 static const float
20 one = 1.0000000000e+00, /* 0x3F800000 */
21 huge = 1.000e+30;
22
23 /*
24 * The coefficients for the rational approximation were generated over
25 * 0x1p-12f <= x <= 0.5f. The maximum error satisfies log2(e) < -30.084.
26 */
27 static const float
28 pS0 = 1.66666672e-01f, /* 0x3e2aaaab */
29 pS1 = -1.19510300e-01f, /* 0xbdf4c1d1 */
30 pS2 = 5.47002675e-03f, /* 0x3bb33de9 */
31 qS1 = -1.16706085e+00f, /* 0xbf956240 */
32 qS2 = 2.90115148e-01f; /* 0x3e9489f9 */
33
34 static const double
35 pio2 = 1.570796326794896558e+00;
36
37 float
asinf(float x)38 asinf(float x)
39 {
40 double s;
41 float t,w,p,q;
42 int32_t hx,ix;
43 GET_FLOAT_WORD(hx,x);
44 ix = hx&0x7fffffff;
45 if(ix>=0x3f800000) { /* |x| >= 1 */
46 if(ix==0x3f800000) /* |x| == 1 */
47 return x*pio2; /* asin(+-1) = +-pi/2 with inexact */
48 return (x-x)/(x-x); /* asin(|x|>1) is NaN */
49 } else if (ix<0x3f000000) { /* |x|<0.5 */
50 if(ix<0x39800000) { /* |x| < 2**-12 */
51 if(huge+x>one) return x;/* return x with inexact if x!=0*/
52 }
53 t = x*x;
54 p = t*(pS0+t*(pS1+t*pS2));
55 q = one+t*(qS1+t*qS2);
56 w = p/q;
57 return x+x*w;
58 }
59 /* 1> |x|>= 0.5 */
60 w = one-fabsf(x);
61 t = w*(float)0.5;
62 p = t*(pS0+t*(pS1+t*pS2));
63 q = one+t*(qS1+t*qS2);
64 s = sqrt(t);
65 w = p/q;
66 t = pio2-2.0*(s+s*w);
67 if(hx>0) return t; else return -t;
68 }
69