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/* origin: FreeBSD /usr/src/lib/msun/src/e_atan2.c */
/*
* ====================================================
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
*
* Developed at SunSoft, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*
*/
/* atan2(y,x)
* Method :
* 1. Reduce y to positive by atan2(y,x)=-atan2(-y,x).
* 2. Reduce x to positive by (if x and y are unexceptional):
* ARG (x+iy) = arctan(y/x) ... if x > 0,
* ARG (x+iy) = pi - arctan[y/(-x)] ... if x < 0,
*
* Special cases:
*
* ATAN2((anything), NaN ) is NaN;
* ATAN2(NAN , (anything) ) is NaN;
* ATAN2(+-0, +(anything but NaN)) is +-0 ;
* ATAN2(+-0, -(anything but NaN)) is +-pi ;
* ATAN2(+-(anything but 0 and NaN), 0) is +-pi/2;
* ATAN2(+-(anything but INF and NaN), +INF) is +-0 ;
* ATAN2(+-(anything but INF and NaN), -INF) is +-pi;
* ATAN2(+-INF,+INF ) is +-pi/4 ;
* ATAN2(+-INF,-INF ) is +-3pi/4;
* ATAN2(+-INF, (anything but,0,NaN, and INF)) is +-pi/2;
*
* 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" // for EXTRACT_WORDS
#include <math.h> // for atan, atan2, fabs, isnan
#include <stdint.h> // for uint32_t
static const double pi = 3.1415926535897931160E+00, /* 0x400921FB, 0x54442D18 */
pi_lo = 1.2246467991473531772E-16; /* 0x3CA1A626, 0x33145C07 */
double atan2(double y, double x)
{
double z;
uint32_t m, lx, ly, ix, iy;
if (isnan(x) || isnan(y))
return x + y;
EXTRACT_WORDS(ix, lx, x);
EXTRACT_WORDS(iy, ly, y);
if ((ix - 0x3ff00000 | lx) == 0) /* x = 1.0 */
return atan(y);
m = ((iy >> 31) & 1) | ((ix >> 30) & 2); /* 2*sign(x)+sign(y) */
ix = ix & 0x7fffffff;
iy = iy & 0x7fffffff;
/* when y = 0 */
if ((iy | ly) == 0) {
switch (m) {
case 0:
case 1:
return y; /* atan(+-0,+anything)=+-0 */
case 2:
return pi; /* atan(+0,-anything) = pi */
case 3:
return -pi; /* atan(-0,-anything) =-pi */
}
}
/* when x = 0 */
if ((ix | lx) == 0)
return m & 1 ? -pi / 2 : pi / 2;
/* when x is INF */
if (ix == 0x7ff00000) {
if (iy == 0x7ff00000) {
switch (m) {
case 0:
return pi / 4; /* atan(+INF,+INF) */
case 1:
return -pi / 4; /* atan(-INF,+INF) */
case 2:
return 3 * pi / 4; /* atan(+INF,-INF) */
case 3:
return -3 * pi / 4; /* atan(-INF,-INF) */
}
} else {
switch (m) {
case 0:
return 0.0; /* atan(+...,+INF) */
case 1:
return -0.0; /* atan(-...,+INF) */
case 2:
return pi; /* atan(+...,-INF) */
case 3:
return -pi; /* atan(-...,-INF) */
}
}
}
/* |y/x| > 0x1p64 */
if (ix + (64 << 20) < iy || iy == 0x7ff00000)
return m & 1 ? -pi / 2 : pi / 2;
/* z = atan(|y/x|) without spurious underflow */
if ((m & 2) && iy + (64 << 20) < ix) /* |y/x| < 0x1p-64, x<0 */
z = 0;
else
z = atan(fabs(y / x));
switch (m) {
case 0:
return z; /* atan(+,+) */
case 1:
return -z; /* atan(-,+) */
case 2:
return pi - (z - pi_lo); /* atan(+,-) */
default: /* case 3 */
return (z - pi_lo) - pi; /* atan(-,-) */
}
}
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