120 lines
3.2 KiB
C
120 lines
3.2 KiB
C
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#ifndef lint
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static char sccsid[] = "@(#)atan2.c 1.1 92/07/30 SMI";
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#endif
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/*
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* Copyright (c) 1988 by Sun Microsystems, Inc.
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*/
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/* atan2(y,x)
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* Code originated from 4.3bsd.
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* Modified by K.C. Ng for SUN 4.0 libm.
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* Method :
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* 1. Reduce y to positive by atan2(y,x)=-atan2(-y,x).
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* 2. Reduce x to positive by (if x and y are unexceptional):
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* ARG (x+iy) = arctan(y/x) ... if x > 0,
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* ARG (x+iy) = pi - arctan[y/(-x)] ... if x < 0,
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*
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* Special cases:
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*
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* ATAN2((anything), NaN ) is NaN;
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* ATAN2(NAN , (anything) ) is NaN;
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* ATAN2(+-0, +(anything but NaN)) is +-0 ;
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* ATAN2(+-0, -(anything but NaN)) is +-PI ;
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* ATAN2(+-(anything but 0 and NaN), 0) is +-PI/2;
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* ATAN2(+-(anything but INF and NaN), +INF) is +-0 ;
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* ATAN2(+-(anything but INF and NaN), -INF) is +-PI;
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* ATAN2(+-INF,+INF ) is +-PI/4 ;
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* ATAN2(+-INF,-INF ) is +-3PI/4;
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* ATAN2(+-INF, (anything but,0,NaN, and INF)) is +-PI/2;
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*
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* Constants:
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* The hexadecimal values are the intended ones for the following constants.
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* The decimal values may be used, provided that the compiler will convert
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* from decimal to binary accurately enough to produce the hexadecimal values
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* shown.
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*/
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#include <math.h>
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#include "libm.h"
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static double
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PIo4 = 7.8539816339744827900E-1 , /*Hex 2^ -1 * 1.921FB54442D18 */
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PIo2 = 1.5707963267948965580E0 , /*Hex 2^ 0 * 1.921FB54442D18 */
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PI = 3.1415926535897931160E0 ; /*Hex 2^ 1 * 1.921FB54442D18 */
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static double PI_lo[] = {
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1.2246467991473531772E-16, /* lo part of pi */
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1.2246063538223772582E-16, /* lo part of 66 bits pi */
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0.0, /* lo part of 53 bits pi */
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};
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static double dummy(x)
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double x ;
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{
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return x ;
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}
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double atan2(y,x)
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double y,x;
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{
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static double zero=0;
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double t,z;
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int k,m,signy,signx;
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if(x!=x||y!=y) return x+y; /* return NaN if x or y is NAN */
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signy = signbit(y) ;
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signx = signbit(x) ;
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if(x==1.0) return atan(y);
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m = signy+signx+signx;
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/* when y = 0 */
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if(y==zero)
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if(x==zero) return SVID_libm_err(x,y,3);
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else
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switch(m) {
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case 0: return y ; /* atan(+0,+anything) */
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case 1: return y ; /* atan(-0,+anything) */
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case 2: return PI; /* atan(+0,-anything) */
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case 3: return -PI; /* atan(-0,-anything) */
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}
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/* when x = 0 */
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if(x==zero) return (signy==1)? -PIo2: PIo2;
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/* when x is INF */
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if(!finite(x))
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if(!finite(y)) {
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switch(m) {
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case 0: return PIo4 ; /* atan(+INF,+INF) */
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case 1: return -PIo4 ; /* atan(-INF,+INF) */
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case 2: return 3*PIo4; /* atan(+INF,-INF) */
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case 3: return -3*PIo4; /* atan(-INF,-INF) */
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}
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} else {
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switch(m) {
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case 0: return zero ; /* atan(+...,+INF) */
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case 1: return -zero ; /* atan(-...,+INF) */
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case 2: return PI ; /* atan(+...,-INF) */
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case 3: return -PI ; /* atan(-...,-INF) */
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}
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}
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/* when y is INF */
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if(!finite(y)) return (signy==1)? -PIo2: PIo2;
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/* compute y/x */
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x=fabs(x);
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y=fabs(y);
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t=PI_lo[(int)fp_pi];
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k = (ilogb(y)-ilogb(x));
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if(k > 60) z=PIo2+0.5*t; else if(m>1&&k<-60) z=0.0; else z=atan(y/x);
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switch (m) {
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case 0: return z ; /* atan(+,+) */
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case 1: return -dummy(z) ; /* atan(-,+) */
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case 2: return PI-(z-t); /* atan(+,-) */
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case 3: return (z-t)-PI; /* atan(-,-) */
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}
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}
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