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 "math.h" 37 #include "math_private.h" 38 39 static const double atanhi[] = { 40 4.63647609000806093515e-01, /* atan(0.5)hi 0x3FDDAC67, 0x0561BB4F */ 41 7.85398163397448278999e-01, /* atan(1.0)hi 0x3FE921FB, 0x54442D18 */ 42 9.82793723247329054082e-01, /* atan(1.5)hi 0x3FEF730B, 0xD281F69B */ 43 1.57079632679489655800e+00, /* atan(inf)hi 0x3FF921FB, 0x54442D18 */ 44 }; 45 46 static const double atanlo[] = { 47 2.26987774529616870924e-17, /* atan(0.5)lo 0x3C7A2B7F, 0x222F65E2 */ 48 3.06161699786838301793e-17, /* atan(1.0)lo 0x3C81A626, 0x33145C07 */ 49 1.39033110312309984516e-17, /* atan(1.5)lo 0x3C700788, 0x7AF0CBBD */ 50 6.12323399573676603587e-17, /* atan(inf)lo 0x3C91A626, 0x33145C07 */ 51 }; 52 53 static const double aT[] = { 54 3.33333333333329318027e-01, /* 0x3FD55555, 0x5555550D */ 55 -1.99999999998764832476e-01, /* 0xBFC99999, 0x9998EBC4 */ 56 1.42857142725034663711e-01, /* 0x3FC24924, 0x920083FF */ 57 -1.11111104054623557880e-01, /* 0xBFBC71C6, 0xFE231671 */ 58 9.09088713343650656196e-02, /* 0x3FB745CD, 0xC54C206E */ 59 -7.69187620504482999495e-02, /* 0xBFB3B0F2, 0xAF749A6D */ 60 6.66107313738753120669e-02, /* 0x3FB10D66, 0xA0D03D51 */ 61 -5.83357013379057348645e-02, /* 0xBFADDE2D, 0x52DEFD9A */ 62 4.97687799461593236017e-02, /* 0x3FA97B4B, 0x24760DEB */ 63 -3.65315727442169155270e-02, /* 0xBFA2B444, 0x2C6A6C2F */ 64 1.62858201153657823623e-02, /* 0x3F90AD3A, 0xE322DA11 */ 65 }; 66 67 static const double 68 one = 1.0, 69 huge = 1.0e300; 70 71 double 72 atan(double x) 73 { 74 double w,s1,s2,z; 75 int32_t ix,hx,id; 76 77 GET_HIGH_WORD(hx,x); 78 ix = hx&0x7fffffff; 79 if(ix>=0x44100000) { /* if |x| >= 2^66 */ 80 u_int32_t low; 81 GET_LOW_WORD(low,x); 82 if(ix>0x7ff00000|| 83 (ix==0x7ff00000&&(low!=0))) 84 return x+x; /* NaN */ 85 if(hx>0) return atanhi[3]+atanlo[3]; 86 else return -atanhi[3]-atanlo[3]; 87 } if (ix < 0x3fdc0000) { /* |x| < 0.4375 */ 88 if (ix < 0x3e200000) { /* |x| < 2^-29 */ 89 if(huge+x>one) return x; /* raise inexact */ 90 } 91 id = -1; 92 } else { 93 x = fabs(x); 94 if (ix < 0x3ff30000) { /* |x| < 1.1875 */ 95 if (ix < 0x3fe60000) { /* 7/16 <=|x|<11/16 */ 96 id = 0; x = (2.0*x-one)/(2.0+x); 97 } else { /* 11/16<=|x|< 19/16 */ 98 id = 1; x = (x-one)/(x+one); 99 } 100 } else { 101 if (ix < 0x40038000) { /* |x| < 2.4375 */ 102 id = 2; x = (x-1.5)/(one+1.5*x); 103 } else { /* 2.4375 <= |x| < 2^66 */ 104 id = 3; x = -1.0/x; 105 } 106 }} 107 /* end of argument reduction */ 108 z = x*x; 109 w = z*z; 110 /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */ 111 s1 = z*(aT[0]+w*(aT[2]+w*(aT[4]+w*(aT[6]+w*(aT[8]+w*aT[10]))))); 112 s2 = w*(aT[1]+w*(aT[3]+w*(aT[5]+w*(aT[7]+w*aT[9])))); 113 if (id<0) return x - x*(s1+s2); 114 else { 115 z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x); 116 return (hx<0)? -z:z; 117 } 118 } 119