1 /* s_atanf.c -- float version of s_atan.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 atanhi[] = {
20 4.6364760399e-01, /* atan(0.5)hi 0x3eed6338 */
21 7.8539812565e-01, /* atan(1.0)hi 0x3f490fda */
22 9.8279368877e-01, /* atan(1.5)hi 0x3f7b985e */
23 1.5707962513e+00, /* atan(inf)hi 0x3fc90fda */
24 };
25
26 static const float atanlo[] = {
27 5.0121582440e-09, /* atan(0.5)lo 0x31ac3769 */
28 3.7748947079e-08, /* atan(1.0)lo 0x33222168 */
29 3.4473217170e-08, /* atan(1.5)lo 0x33140fb4 */
30 7.5497894159e-08, /* atan(inf)lo 0x33a22168 */
31 };
32
33 static const float aT[] = {
34 3.3333328366e-01,
35 -1.9999158382e-01,
36 1.4253635705e-01,
37 -1.0648017377e-01,
38 6.1687607318e-02,
39 };
40
41 static const float
42 one = 1.0,
43 huge = 1.0e30;
44
45 float
atanf(float x)46 atanf(float x)
47 {
48 float w,s1,s2,z;
49 int32_t ix,hx,id;
50
51 GET_FLOAT_WORD(hx,x);
52 ix = hx&0x7fffffff;
53 if(ix>=0x4c800000) { /* if |x| >= 2**26 */
54 if(ix>0x7f800000)
55 return x+x; /* NaN */
56 if(hx>0) return atanhi[3]+*(volatile float *)&atanlo[3];
57 else return -atanhi[3]-*(volatile float *)&atanlo[3];
58 } if (ix < 0x3ee00000) { /* |x| < 0.4375 */
59 if (ix < 0x39800000) { /* |x| < 2**-12 */
60 if(huge+x>one) return x; /* raise inexact */
61 }
62 id = -1;
63 } else {
64 x = fabsf(x);
65 if (ix < 0x3f980000) { /* |x| < 1.1875 */
66 if (ix < 0x3f300000) { /* 7/16 <=|x|<11/16 */
67 id = 0; x = ((float)2.0*x-one)/((float)2.0+x);
68 } else { /* 11/16<=|x|< 19/16 */
69 id = 1; x = (x-one)/(x+one);
70 }
71 } else {
72 if (ix < 0x401c0000) { /* |x| < 2.4375 */
73 id = 2; x = (x-(float)1.5)/(one+(float)1.5*x);
74 } else { /* 2.4375 <= |x| < 2**26 */
75 id = 3; x = -(float)1.0/x;
76 }
77 }}
78 /* end of argument reduction */
79 z = x*x;
80 w = z*z;
81 /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
82 s1 = z*(aT[0]+w*(aT[2]+w*aT[4]));
83 s2 = w*(aT[1]+w*aT[3]);
84 if (id<0) return x - x*(s1+s2);
85 else {
86 z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x);
87 return (hx<0)? -z:z;
88 }
89 }
90