zenilib  0.5.3.0
s_atan.c
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1 /*
2  * ====================================================
4  *
5  * Developed at SunPro, a Sun Microsystems, Inc. business.
6  * Permission to use, copy, modify, and distribute this
7  * software is freely granted, provided that this notice
8  * is preserved.
9  * ====================================================
10  */
11
12 /* atan(x)
13  * Method
14  * 1. Reduce x to positive by atan(x) = -atan(-x).
15  * 2. According to the integer k=4t+0.25 chopped, t=x, the argument
16  * is further reduced to one of the following intervals and the
17  * arctangent of t is evaluated by the corresponding formula:
18  *
19  * [0,7/16] atan(x) = t-t^3*(a1+t^2*(a2+...(a10+t^2*a11)...)
20  * [7/16,11/16] atan(x) = atan(1/2) + atan( (t-0.5)/(1+t/2) )
21  * [11/16.19/16] atan(x) = atan( 1 ) + atan( (t-1)/(1+t) )
22  * [19/16,39/16] atan(x) = atan(3/2) + atan( (t-1.5)/(1+1.5t) )
23  * [39/16,INF] atan(x) = atan(INF) + atan( -1/t )
24  *
25  * Constants:
26  * The hexadecimal values are the intended ones for the following
27  * constants. The decimal values may be used, provided that the
28  * compiler will convert from decimal to binary accurately enough
29  * to produce the hexadecimal values shown.
30  */
31
32 #include "math_libm.h"
33 #include "math_private.h"
34
35 static const double atanhi[] = {
36  4.63647609000806093515e-01, /* atan(0.5)hi 0x3FDDAC67, 0x0561BB4F */
37  7.85398163397448278999e-01, /* atan(1.0)hi 0x3FE921FB, 0x54442D18 */
38  9.82793723247329054082e-01, /* atan(1.5)hi 0x3FEF730B, 0xD281F69B */
39  1.57079632679489655800e+00, /* atan(inf)hi 0x3FF921FB, 0x54442D18 */
40 };
41
42 static const double atanlo[] = {
43  2.26987774529616870924e-17, /* atan(0.5)lo 0x3C7A2B7F, 0x222F65E2 */
44  3.06161699786838301793e-17, /* atan(1.0)lo 0x3C81A626, 0x33145C07 */
45  1.39033110312309984516e-17, /* atan(1.5)lo 0x3C700788, 0x7AF0CBBD */
46  6.12323399573676603587e-17, /* atan(inf)lo 0x3C91A626, 0x33145C07 */
47 };
48
49 static const double aT[] = {
50  3.33333333333329318027e-01, /* 0x3FD55555, 0x5555550D */
51  -1.99999999998764832476e-01, /* 0xBFC99999, 0x9998EBC4 */
52  1.42857142725034663711e-01, /* 0x3FC24924, 0x920083FF */
53  -1.11111104054623557880e-01, /* 0xBFBC71C6, 0xFE231671 */
54  9.09088713343650656196e-02, /* 0x3FB745CD, 0xC54C206E */
55  -7.69187620504482999495e-02, /* 0xBFB3B0F2, 0xAF749A6D */
56  6.66107313738753120669e-02, /* 0x3FB10D66, 0xA0D03D51 */
57  -5.83357013379057348645e-02, /* 0xBFADDE2D, 0x52DEFD9A */
58  4.97687799461593236017e-02, /* 0x3FA97B4B, 0x24760DEB */
59  -3.65315727442169155270e-02, /* 0xBFA2B444, 0x2C6A6C2F */
60  1.62858201153657823623e-02, /* 0x3F90AD3A, 0xE322DA11 */
61 };
62
63 static const double
64 one = 1.0,
65 huge = 1.0e300;
66
67 double atan(double x)
68 {
69  double w,s1,s2,z;
70  int32_t ix,hx,id;
71
72  GET_HIGH_WORD(hx,x);
73  ix = hx&0x7fffffff;
74  if(ix>=0x44100000) { /* if |x| >= 2^66 */
75  u_int32_t low;
76  GET_LOW_WORD(low,x);
77  if(ix>0x7ff00000||
78  (ix==0x7ff00000&&(low!=0)))
79  return x+x; /* NaN */
80  if(hx>0) return atanhi[3]+atanlo[3];
81  else return -atanhi[3]-atanlo[3];
82  } if (ix < 0x3fdc0000) { /* |x| < 0.4375 */
83  if (ix < 0x3e200000) { /* |x| < 2^-29 */
84  if(huge+x>one) return x; /* raise inexact */
85  }
86  id = -1;
87  } else {
88  x = fabs(x);
89  if (ix < 0x3ff30000) { /* |x| < 1.1875 */
90  if (ix < 0x3fe60000) { /* 7/16 <=|x|<11/16 */
91  id = 0; x = (2.0*x-one)/(2.0+x);
92  } else { /* 11/16<=|x|< 19/16 */
93  id = 1; x = (x-one)/(x+one);
94  }
95  } else {
96  if (ix < 0x40038000) { /* |x| < 2.4375 */
97  id = 2; x = (x-1.5)/(one+1.5*x);
98  } else { /* 2.4375 <= |x| < 2^66 */
99  id = 3; x = -1.0/x;
100  }
101  }}
102  /* end of argument reduction */
103  z = x*x;
104  w = z*z;
105  /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
106  s1 = z*(aT[0]+w*(aT[2]+w*(aT[4]+w*(aT[6]+w*(aT[8]+w*aT[10])))));
107  s2 = w*(aT[1]+w*(aT[3]+w*(aT[5]+w*(aT[7]+w*aT[9]))));
108  if (id<0) return x - x*(s1+s2);
109  else {
110  z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x);
111  return (hx<0)? -z:z;
112  }
113 }
static const double aT[]
Definition: s_atan.c:49
#define GET_HIGH_WORD(i, d)
Definition: math_private.h:102
GET_LOW_WORD(low, x)
EGLSurface EGLint x
Definition: eglext.h:293
long int32_t
Definition: types.h:9
GLuint id
Definition: gl2ext.h:1142
static const double one
Definition: s_atan.c:64
unsigned int u_int32_t
Definition: math_private.h:29
static const double atanhi[]
Definition: s_atan.c:35
#define libm_hidden_def(x)
Definition: math_private.h:26
GLuint GLfloat GLfloat GLfloat GLfloat GLfloat GLfloat GLfloat GLfloat s1
Definition: glew.h:11582
int32_t hx
Definition: e_log.c:102
int32_t ix
Definition: e_rem_pio2.c:100
u_int32_t low
Definition: e_rem_pio2.c:101
static const double huge
Definition: s_atan.c:65
GLint GLint GLint GLint z
Definition: gl2ext.h:1214
GLint GLint GLint GLint GLint w
Definition: gl2ext.h:1215
double atan(double x)
Definition: s_atan.c:67
double fabs(double x)
Definition: s_fabs.c:29
static const double atanlo[]
Definition: s_atan.c:42