1 /* @(#)s_atan.c 5.1 93/09/24 */
2 /*
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5 *
6 * Developed at SunPro, a Sun Microsystems, Inc. business.
7 * Permission to use, copy, modify, and distribute this
8 * software is freely granted, provided that this notice
9 * is preserved.
10 * ====================================================
11 */
12
13 #include <sys/cdefs.h>
14 __FBSDID("$FreeBSD$");
15
16 /* atan(x)
17 * Method
18 * 1. Reduce x to positive by atan(x) = -atan(-x).
19 * 2. According to the integer k=4t+0.25 chopped, t=x, the argument
20 * is further reduced to one of the following intervals and the
21 * arctangent of t is evaluated by the corresponding formula:
22 *
23 * [0,7/16] atan(x) = t-t^3*(a1+t^2*(a2+...(a10+t^2*a11)...)
24 * [7/16,11/16] atan(x) = atan(1/2) + atan( (t-0.5)/(1+t/2) )
25 * [11/16.19/16] atan(x) = atan( 1 ) + atan( (t-1)/(1+t) )
26 * [19/16,39/16] atan(x) = atan(3/2) + atan( (t-1.5)/(1+1.5t) )
27 * [39/16,INF] atan(x) = atan(INF) + atan( -1/t )
28 *
29 * Constants:
30 * The hexadecimal values are the intended ones for the following
31 * constants. The decimal values may be used, provided that the
32 * compiler will convert from decimal to binary accurately enough
33 * to produce the hexadecimal values shown.
34 */
35
36 #include <float.h>
37
38 #include "math.h"
39 #include "math_private.h"
40
41 static const double atanhi[] = {
42 4.63647609000806093515e-01, /* atan(0.5)hi 0x3FDDAC67, 0x0561BB4F */
43 7.85398163397448278999e-01, /* atan(1.0)hi 0x3FE921FB, 0x54442D18 */
44 9.82793723247329054082e-01, /* atan(1.5)hi 0x3FEF730B, 0xD281F69B */
45 1.57079632679489655800e+00, /* atan(inf)hi 0x3FF921FB, 0x54442D18 */
46 };
47
48 static const double atanlo[] = {
49 2.26987774529616870924e-17, /* atan(0.5)lo 0x3C7A2B7F, 0x222F65E2 */
50 3.06161699786838301793e-17, /* atan(1.0)lo 0x3C81A626, 0x33145C07 */
51 1.39033110312309984516e-17, /* atan(1.5)lo 0x3C700788, 0x7AF0CBBD */
52 6.12323399573676603587e-17, /* atan(inf)lo 0x3C91A626, 0x33145C07 */
53 };
54
55 static const double aT[] = {
56 3.33333333333329318027e-01, /* 0x3FD55555, 0x5555550D */
57 -1.99999999998764832476e-01, /* 0xBFC99999, 0x9998EBC4 */
58 1.42857142725034663711e-01, /* 0x3FC24924, 0x920083FF */
59 -1.11111104054623557880e-01, /* 0xBFBC71C6, 0xFE231671 */
60 9.09088713343650656196e-02, /* 0x3FB745CD, 0xC54C206E */
61 -7.69187620504482999495e-02, /* 0xBFB3B0F2, 0xAF749A6D */
62 6.66107313738753120669e-02, /* 0x3FB10D66, 0xA0D03D51 */
63 -5.83357013379057348645e-02, /* 0xBFADDE2D, 0x52DEFD9A */
64 4.97687799461593236017e-02, /* 0x3FA97B4B, 0x24760DEB */
65 -3.65315727442169155270e-02, /* 0xBFA2B444, 0x2C6A6C2F */
66 1.62858201153657823623e-02, /* 0x3F90AD3A, 0xE322DA11 */
67 };
68
69 static const double
70 one = 1.0,
71 huge = 1.0e300;
72
73 double
atan(double x)74 atan(double x)
75 {
76 double w,s1,s2,z;
77 int32_t ix,hx,id;
78
79 GET_HIGH_WORD(hx,x);
80 ix = hx&0x7fffffff;
81 if(ix>=0x44100000) { /* if |x| >= 2^66 */
82 u_int32_t low;
83 GET_LOW_WORD(low,x);
84 if(ix>0x7ff00000||
85 (ix==0x7ff00000&&(low!=0)))
86 return x+x; /* NaN */
87 if(hx>0) return atanhi[3]+*(volatile double *)&atanlo[3];
88 else return -atanhi[3]-*(volatile double *)&atanlo[3];
89 } if (ix < 0x3fdc0000) { /* |x| < 0.4375 */
90 if (ix < 0x3e400000) { /* |x| < 2^-27 */
91 if(huge+x>one) return x; /* raise inexact */
92 }
93 id = -1;
94 } else {
95 x = fabs(x);
96 if (ix < 0x3ff30000) { /* |x| < 1.1875 */
97 if (ix < 0x3fe60000) { /* 7/16 <=|x|<11/16 */
98 id = 0; x = (2.0*x-one)/(2.0+x);
99 } else { /* 11/16<=|x|< 19/16 */
100 id = 1; x = (x-one)/(x+one);
101 }
102 } else {
103 if (ix < 0x40038000) { /* |x| < 2.4375 */
104 id = 2; x = (x-1.5)/(one+1.5*x);
105 } else { /* 2.4375 <= |x| < 2^66 */
106 id = 3; x = -1.0/x;
107 }
108 }}
109 /* end of argument reduction */
110 z = x*x;
111 w = z*z;
112 /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
113 s1 = z*(aT[0]+w*(aT[2]+w*(aT[4]+w*(aT[6]+w*(aT[8]+w*aT[10])))));
114 s2 = w*(aT[1]+w*(aT[3]+w*(aT[5]+w*(aT[7]+w*aT[9]))));
115 if (id<0) return x - x*(s1+s2);
116 else {
117 z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x);
118 return (hx<0)? -z:z;
119 }
120 }
121
122 #if LDBL_MANT_DIG == 53
123 __weak_reference(atan, atanl);
124 #endif
125