e_atan2.c revision 50476
1/* @(#)e_atan2.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#ifndef lint 14static char rcsid[] = "$FreeBSD: head/lib/msun/src/e_atan2.c 50476 1999-08-28 00:22:10Z peter $"; 15#endif 16 17/* __ieee754_atan2(y,x) 18 * Method : 19 * 1. Reduce y to positive by atan2(y,x)=-atan2(-y,x). 20 * 2. Reduce x to positive by (if x and y are unexceptional): 21 * ARG (x+iy) = arctan(y/x) ... if x > 0, 22 * ARG (x+iy) = pi - arctan[y/(-x)] ... if x < 0, 23 * 24 * Special cases: 25 * 26 * ATAN2((anything), NaN ) is NaN; 27 * ATAN2(NAN , (anything) ) is NaN; 28 * ATAN2(+-0, +(anything but NaN)) is +-0 ; 29 * ATAN2(+-0, -(anything but NaN)) is +-pi ; 30 * ATAN2(+-(anything but 0 and NaN), 0) is +-pi/2; 31 * ATAN2(+-(anything but INF and NaN), +INF) is +-0 ; 32 * ATAN2(+-(anything but INF and NaN), -INF) is +-pi; 33 * ATAN2(+-INF,+INF ) is +-pi/4 ; 34 * ATAN2(+-INF,-INF ) is +-3pi/4; 35 * ATAN2(+-INF, (anything but,0,NaN, and INF)) is +-pi/2; 36 * 37 * Constants: 38 * The hexadecimal values are the intended ones for the following 39 * constants. The decimal values may be used, provided that the 40 * compiler will convert from decimal to binary accurately enough 41 * to produce the hexadecimal values shown. 42 */ 43 44#include "math.h" 45#include "math_private.h" 46 47#ifdef __STDC__ 48static const double 49#else 50static double 51#endif 52tiny = 1.0e-300, 53zero = 0.0, 54pi_o_4 = 7.8539816339744827900E-01, /* 0x3FE921FB, 0x54442D18 */ 55pi_o_2 = 1.5707963267948965580E+00, /* 0x3FF921FB, 0x54442D18 */ 56pi = 3.1415926535897931160E+00, /* 0x400921FB, 0x54442D18 */ 57pi_lo = 1.2246467991473531772E-16; /* 0x3CA1A626, 0x33145C07 */ 58 59#ifdef __STDC__ 60 double __generic___ieee754_atan2(double y, double x) 61#else 62 double __generic___ieee754_atan2(y,x) 63 double y,x; 64#endif 65{ 66 double z; 67 int32_t k,m,hx,hy,ix,iy; 68 u_int32_t lx,ly; 69 70 EXTRACT_WORDS(hx,lx,x); 71 ix = hx&0x7fffffff; 72 EXTRACT_WORDS(hy,ly,y); 73 iy = hy&0x7fffffff; 74 if(((ix|((lx|-lx)>>31))>0x7ff00000)|| 75 ((iy|((ly|-ly)>>31))>0x7ff00000)) /* x or y is NaN */ 76 return x+y; 77 if(((hx-0x3ff00000)|lx)==0) return atan(y); /* x=1.0 */ 78 m = ((hy>>31)&1)|((hx>>30)&2); /* 2*sign(x)+sign(y) */ 79 80 /* when y = 0 */ 81 if((iy|ly)==0) { 82 switch(m) { 83 case 0: 84 case 1: return y; /* atan(+-0,+anything)=+-0 */ 85 case 2: return pi+tiny;/* atan(+0,-anything) = pi */ 86 case 3: return -pi-tiny;/* atan(-0,-anything) =-pi */ 87 } 88 } 89 /* when x = 0 */ 90 if((ix|lx)==0) return (hy<0)? -pi_o_2-tiny: pi_o_2+tiny; 91 92 /* when x is INF */ 93 if(ix==0x7ff00000) { 94 if(iy==0x7ff00000) { 95 switch(m) { 96 case 0: return pi_o_4+tiny;/* atan(+INF,+INF) */ 97 case 1: return -pi_o_4-tiny;/* atan(-INF,+INF) */ 98 case 2: return 3.0*pi_o_4+tiny;/*atan(+INF,-INF)*/ 99 case 3: return -3.0*pi_o_4-tiny;/*atan(-INF,-INF)*/ 100 } 101 } else { 102 switch(m) { 103 case 0: return zero ; /* atan(+...,+INF) */ 104 case 1: return -zero ; /* atan(-...,+INF) */ 105 case 2: return pi+tiny ; /* atan(+...,-INF) */ 106 case 3: return -pi-tiny ; /* atan(-...,-INF) */ 107 } 108 } 109 } 110 /* when y is INF */ 111 if(iy==0x7ff00000) return (hy<0)? -pi_o_2-tiny: pi_o_2+tiny; 112 113 /* compute y/x */ 114 k = (iy-ix)>>20; 115 if(k > 60) z=pi_o_2+0.5*pi_lo; /* |y/x| > 2**60 */ 116 else if(hx<0&&k<-60) z=0.0; /* |y|/x < -2**60 */ 117 else z=atan(fabs(y/x)); /* safe to do y/x */ 118 switch (m) { 119 case 0: return z ; /* atan(+,+) */ 120 case 1: { 121 u_int32_t zh; 122 GET_HIGH_WORD(zh,z); 123 SET_HIGH_WORD(z,zh ^ 0x80000000); 124 } 125 return z ; /* atan(-,+) */ 126 case 2: return pi-(z-pi_lo);/* atan(+,-) */ 127 default: /* case 3 */ 128 return (z-pi_lo)-pi;/* atan(-,-) */ 129 } 130} 131