/* @(#)s_atan.c 5.1 93/09/24 */ /* * ==================================================== * 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. * ==================================================== */ #ifndef lint static char rcsid[] = "\$Id: s_atan.c,v 1.6 1994/08/18 23:06:23 jtc Exp \$"; #endif /* 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 "math.h" #include "math_private.h" #ifdef __STDC__ static const double atanhi[] = { #else static double atanhi[] = { #endif 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 */ }; #ifdef __STDC__ static const double atanlo[] = { #else static double atanlo[] = { #endif 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 */ }; #ifdef __STDC__ static const double aT[] = { #else static double aT[] = { #endif 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 */ }; #ifdef __STDC__ static const double #else static double #endif one = 1.0, huge = 1.0e300; #ifdef __STDC__ double atan(double x) #else double atan(x) double x; #endif { double w,s1,s2,z; int32_t ix,hx,id; GET_HIGH_WORD(hx,x); ix = hx&0x7fffffff; if(ix>=0x44100000) { /* if |x| >= 2^66 */ u_int32_t low; GET_LOW_WORD(low,x); if(ix>0x7ff00000|| (ix==0x7ff00000&&(low!=0))) return x+x; /* NaN */ if(hx>0) return atanhi[3]+atanlo[3]; else return -atanhi[3]-atanlo[3]; } if (ix < 0x3fdc0000) { /* |x| < 0.4375 */ if (ix < 0x3e200000) { /* |x| < 2^-29 */ if(huge+x>one) return x; /* raise inexact */ } 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-one)/(2.0+x); } else { /* 11/16<=|x|< 19/16 */ id = 1; x = (x-one)/(x+one); } } else { if (ix < 0x40038000) { /* |x| < 2.4375 */ id = 2; x = (x-1.5)/(one+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); else { z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x); return (hx<0)? -z:z; } }