e_atan2.c revision 141296
1141296Sdas 2141296Sdas/* @(#)e_atan2.c 1.3 95/01/18 */ 32116Sjkh/* 42116Sjkh * ==================================================== 52116Sjkh * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 62116Sjkh * 7141296Sdas * Developed at SunSoft, a Sun Microsystems, Inc. business. 82116Sjkh * Permission to use, copy, modify, and distribute this 9141296Sdas * software is freely granted, provided that this notice 102116Sjkh * is preserved. 112116Sjkh * ==================================================== 12141296Sdas * 132116Sjkh */ 142116Sjkh 152116Sjkh#ifndef lint 1650476Speterstatic char rcsid[] = "$FreeBSD: head/lib/msun/src/e_atan2.c 141296 2005-02-04 18:26:06Z das $"; 172116Sjkh#endif 182116Sjkh 192116Sjkh/* __ieee754_atan2(y,x) 202116Sjkh * Method : 212116Sjkh * 1. Reduce y to positive by atan2(y,x)=-atan2(-y,x). 22141296Sdas * 2. Reduce x to positive by (if x and y are unexceptional): 232116Sjkh * ARG (x+iy) = arctan(y/x) ... if x > 0, 242116Sjkh * ARG (x+iy) = pi - arctan[y/(-x)] ... if x < 0, 252116Sjkh * 262116Sjkh * Special cases: 272116Sjkh * 282116Sjkh * ATAN2((anything), NaN ) is NaN; 292116Sjkh * ATAN2(NAN , (anything) ) is NaN; 302116Sjkh * ATAN2(+-0, +(anything but NaN)) is +-0 ; 312116Sjkh * ATAN2(+-0, -(anything but NaN)) is +-pi ; 322116Sjkh * ATAN2(+-(anything but 0 and NaN), 0) is +-pi/2; 332116Sjkh * ATAN2(+-(anything but INF and NaN), +INF) is +-0 ; 342116Sjkh * ATAN2(+-(anything but INF and NaN), -INF) is +-pi; 352116Sjkh * ATAN2(+-INF,+INF ) is +-pi/4 ; 362116Sjkh * ATAN2(+-INF,-INF ) is +-3pi/4; 372116Sjkh * ATAN2(+-INF, (anything but,0,NaN, and INF)) is +-pi/2; 382116Sjkh * 392116Sjkh * Constants: 40141296Sdas * The hexadecimal values are the intended ones for the following 41141296Sdas * constants. The decimal values may be used, provided that the 42141296Sdas * compiler will convert from decimal to binary accurately enough 432116Sjkh * to produce the hexadecimal values shown. 442116Sjkh */ 452116Sjkh 462116Sjkh#include "math.h" 472116Sjkh#include "math_private.h" 482116Sjkh 498870Srgrimesstatic const double 502116Sjkhtiny = 1.0e-300, 512116Sjkhzero = 0.0, 522116Sjkhpi_o_4 = 7.8539816339744827900E-01, /* 0x3FE921FB, 0x54442D18 */ 532116Sjkhpi_o_2 = 1.5707963267948965580E+00, /* 0x3FF921FB, 0x54442D18 */ 542116Sjkhpi = 3.1415926535897931160E+00, /* 0x400921FB, 0x54442D18 */ 552116Sjkhpi_lo = 1.2246467991473531772E-16; /* 0x3CA1A626, 0x33145C07 */ 562116Sjkh 5797407Salfreddouble 58117912Speter__ieee754_atan2(double y, double x) 598870Srgrimes{ 602116Sjkh double z; 612116Sjkh int32_t k,m,hx,hy,ix,iy; 622116Sjkh u_int32_t lx,ly; 632116Sjkh 642116Sjkh EXTRACT_WORDS(hx,lx,x); 652116Sjkh ix = hx&0x7fffffff; 662116Sjkh EXTRACT_WORDS(hy,ly,y); 672116Sjkh iy = hy&0x7fffffff; 682116Sjkh if(((ix|((lx|-lx)>>31))>0x7ff00000)|| 692116Sjkh ((iy|((ly|-ly)>>31))>0x7ff00000)) /* x or y is NaN */ 702116Sjkh return x+y; 71141296Sdas if((hx-0x3ff00000|lx)==0) return atan(y); /* x=1.0 */ 722116Sjkh m = ((hy>>31)&1)|((hx>>30)&2); /* 2*sign(x)+sign(y) */ 732116Sjkh 742116Sjkh /* when y = 0 */ 752116Sjkh if((iy|ly)==0) { 762116Sjkh switch(m) { 77141296Sdas case 0: 782116Sjkh case 1: return y; /* atan(+-0,+anything)=+-0 */ 792116Sjkh case 2: return pi+tiny;/* atan(+0,-anything) = pi */ 802116Sjkh case 3: return -pi-tiny;/* atan(-0,-anything) =-pi */ 812116Sjkh } 822116Sjkh } 832116Sjkh /* when x = 0 */ 842116Sjkh if((ix|lx)==0) return (hy<0)? -pi_o_2-tiny: pi_o_2+tiny; 85141296Sdas 862116Sjkh /* when x is INF */ 872116Sjkh if(ix==0x7ff00000) { 882116Sjkh if(iy==0x7ff00000) { 892116Sjkh switch(m) { 902116Sjkh case 0: return pi_o_4+tiny;/* atan(+INF,+INF) */ 912116Sjkh case 1: return -pi_o_4-tiny;/* atan(-INF,+INF) */ 922116Sjkh case 2: return 3.0*pi_o_4+tiny;/*atan(+INF,-INF)*/ 932116Sjkh case 3: return -3.0*pi_o_4-tiny;/*atan(-INF,-INF)*/ 942116Sjkh } 952116Sjkh } else { 962116Sjkh switch(m) { 972116Sjkh case 0: return zero ; /* atan(+...,+INF) */ 982116Sjkh case 1: return -zero ; /* atan(-...,+INF) */ 992116Sjkh case 2: return pi+tiny ; /* atan(+...,-INF) */ 1002116Sjkh case 3: return -pi-tiny ; /* atan(-...,-INF) */ 1012116Sjkh } 1022116Sjkh } 1032116Sjkh } 1042116Sjkh /* when y is INF */ 1052116Sjkh if(iy==0x7ff00000) return (hy<0)? -pi_o_2-tiny: pi_o_2+tiny; 1062116Sjkh 1072116Sjkh /* compute y/x */ 1082116Sjkh k = (iy-ix)>>20; 1092116Sjkh if(k > 60) z=pi_o_2+0.5*pi_lo; /* |y/x| > 2**60 */ 1102116Sjkh else if(hx<0&&k<-60) z=0.0; /* |y|/x < -2**60 */ 1112116Sjkh else z=atan(fabs(y/x)); /* safe to do y/x */ 1122116Sjkh switch (m) { 1132116Sjkh case 0: return z ; /* atan(+,+) */ 1142116Sjkh case 1: { 1152116Sjkh u_int32_t zh; 1162116Sjkh GET_HIGH_WORD(zh,z); 1172116Sjkh SET_HIGH_WORD(z,zh ^ 0x80000000); 1182116Sjkh } 1192116Sjkh return z ; /* atan(-,+) */ 1202116Sjkh case 2: return pi-(z-pi_lo);/* atan(+,-) */ 1212116Sjkh default: /* case 3 */ 1222116Sjkh return (z-pi_lo)-pi;/* atan(-,-) */ 1232116Sjkh } 1242116Sjkh} 125