summaryrefslogtreecommitdiff log msg author committer range
path: root/src/math/atan.c
blob: 63b0ab25e3cf02ea81bab5a9ee4d99d6c40bb582 (plain)
 ```1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 ``` ``````/* origin: FreeBSD /usr/src/lib/msun/src/s_atan.c */ /* * ==================================================== * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. * * Developed at SunPro, a Sun Microsystems, Inc. business. * Permission to use, copy, modify, and distribute this * software is freely granted, provided that this notice * is preserved. * ==================================================== */ /* atan(x) * Method * 1. Reduce x to positive by atan(x) = -atan(-x). * 2. According to the integer k=4t+0.25 chopped, t=x, the argument * is further reduced to one of the following intervals and the * arctangent of t is evaluated by the corresponding formula: * * [0,7/16] atan(x) = t-t^3*(a1+t^2*(a2+...(a10+t^2*a11)...) * [7/16,11/16] atan(x) = atan(1/2) + atan( (t-0.5)/(1+t/2) ) * [11/16.19/16] atan(x) = atan( 1 ) + atan( (t-1)/(1+t) ) * [19/16,39/16] atan(x) = atan(3/2) + atan( (t-1.5)/(1+1.5t) ) * [39/16,INF] atan(x) = atan(INF) + atan( -1/t ) * * Constants: * The hexadecimal values are the intended ones for the following * constants. The decimal values may be used, provided that the * compiler will convert from decimal to binary accurately enough * to produce the hexadecimal values shown. */ #include "libm.h" static const double atanhi[] = { 4.63647609000806093515e-01, /* atan(0.5)hi 0x3FDDAC67, 0x0561BB4F */ 7.85398163397448278999e-01, /* atan(1.0)hi 0x3FE921FB, 0x54442D18 */ 9.82793723247329054082e-01, /* atan(1.5)hi 0x3FEF730B, 0xD281F69B */ 1.57079632679489655800e+00, /* atan(inf)hi 0x3FF921FB, 0x54442D18 */ }; static const double atanlo[] = { 2.26987774529616870924e-17, /* atan(0.5)lo 0x3C7A2B7F, 0x222F65E2 */ 3.06161699786838301793e-17, /* atan(1.0)lo 0x3C81A626, 0x33145C07 */ 1.39033110312309984516e-17, /* atan(1.5)lo 0x3C700788, 0x7AF0CBBD */ 6.12323399573676603587e-17, /* atan(inf)lo 0x3C91A626, 0x33145C07 */ }; static const double aT[] = { 3.33333333333329318027e-01, /* 0x3FD55555, 0x5555550D */ -1.99999999998764832476e-01, /* 0xBFC99999, 0x9998EBC4 */ 1.42857142725034663711e-01, /* 0x3FC24924, 0x920083FF */ -1.11111104054623557880e-01, /* 0xBFBC71C6, 0xFE231671 */ 9.09088713343650656196e-02, /* 0x3FB745CD, 0xC54C206E */ -7.69187620504482999495e-02, /* 0xBFB3B0F2, 0xAF749A6D */ 6.66107313738753120669e-02, /* 0x3FB10D66, 0xA0D03D51 */ -5.83357013379057348645e-02, /* 0xBFADDE2D, 0x52DEFD9A */ 4.97687799461593236017e-02, /* 0x3FA97B4B, 0x24760DEB */ -3.65315727442169155270e-02, /* 0xBFA2B444, 0x2C6A6C2F */ 1.62858201153657823623e-02, /* 0x3F90AD3A, 0xE322DA11 */ }; double atan(double x) { double_t w,s1,s2,z; uint32_t ix,sign; int id; GET_HIGH_WORD(ix, x); sign = ix >> 31; ix &= 0x7fffffff; if (ix >= 0x44100000) { /* if |x| >= 2^66 */ if (isnan(x)) return x; z = atanhi[3] + 0x1p-120f; return sign ? -z : z; } if (ix < 0x3fdc0000) { /* |x| < 0.4375 */ if (ix < 0x3e400000) { /* |x| < 2^-27 */ if (ix < 0x00100000) /* raise underflow for subnormal x */ FORCE_EVAL((float)x); return x; } id = -1; } else { x = fabs(x); if (ix < 0x3ff30000) { /* |x| < 1.1875 */ if (ix < 0x3fe60000) { /* 7/16 <= |x| < 11/16 */ id = 0; x = (2.0*x-1.0)/(2.0+x); } else { /* 11/16 <= |x| < 19/16 */ id = 1; x = (x-1.0)/(x+1.0); } } else { if (ix < 0x40038000) { /* |x| < 2.4375 */ id = 2; x = (x-1.5)/(1.0+1.5*x); } else { /* 2.4375 <= |x| < 2^66 */ id = 3; x = -1.0/x; } } } /* end of argument reduction */ z = x*x; w = z*z; /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */ s1 = z*(aT[0]+w*(aT[2]+w*(aT[4]+w*(aT[6]+w*(aT[8]+w*aT[10]))))); s2 = w*(aT[1]+w*(aT[3]+w*(aT[5]+w*(aT[7]+w*aT[9])))); if (id < 0) return x - x*(s1+s2); z = atanhi[id] - (x*(s1+s2) - atanlo[id] - x); return sign ? -z : z; } ``````