1/* origin: FreeBSD /usr/src/lib/msun/src/e_atan2f.c */
2/*
3 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
4 */
5/*
6 * ====================================================
7 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
8 *
9 * Developed at SunPro, a Sun Microsystems, Inc. business.
10 * Permission to use, copy, modify, and distribute this
11 * software is freely granted, provided that this notice
12 * is preserved.
13 * ====================================================
14 */
15
16#include "libm.h"
17
18static const float
19pi     = 3.1415927410e+00, /* 0x40490fdb */
20pi_lo  = -8.7422776573e-08; /* 0xb3bbbd2e */
21
22float atan2f(float y, float x)
23{
24	float z;
25	uint32_t m,ix,iy;
26
27	if (isnan(x) || isnan(y))
28		return x+y;
29	GET_FLOAT_WORD(ix, x);
30	GET_FLOAT_WORD(iy, y);
31	if (ix == 0x3f800000)  /* x=1.0 */
32		return atanf(y);
33	m = ((iy>>31)&1) | ((ix>>30)&2);  /* 2*sign(x)+sign(y) */
34	ix &= 0x7fffffff;
35	iy &= 0x7fffffff;
36
37	/* when y = 0 */
38	if (iy == 0) {
39		switch (m) {
40		case 0:
41		case 1: return y;   /* atan(+-0,+anything)=+-0 */
42		case 2: return  pi; /* atan(+0,-anything) = pi */
43		case 3: return -pi; /* atan(-0,-anything) =-pi */
44		}
45	}
46	/* when x = 0 */
47	if (ix == 0)
48		return m&1 ? -pi/2 : pi/2;
49	/* when x is INF */
50	if (ix == 0x7f800000) {
51		if (iy == 0x7f800000) {
52			switch (m) {
53			case 0: return  pi/4; /* atan(+INF,+INF) */
54			case 1: return -pi/4; /* atan(-INF,+INF) */
55			case 2: return 3*pi/4;  /*atan(+INF,-INF)*/
56			case 3: return -3*pi/4; /*atan(-INF,-INF)*/
57			}
58		} else {
59			switch (m) {
60			case 0: return  0.0f;    /* atan(+...,+INF) */
61			case 1: return -0.0f;    /* atan(-...,+INF) */
62			case 2: return  pi; /* atan(+...,-INF) */
63			case 3: return -pi; /* atan(-...,-INF) */
64			}
65		}
66	}
67	/* |y/x| > 0x1p26 */
68	if (ix+(26<<23) < iy || iy == 0x7f800000)
69		return m&1 ? -pi/2 : pi/2;
70
71	/* z = atan(|y/x|) with correct underflow */
72	if ((m&2) && iy+(26<<23) < ix)  /*|y/x| < 0x1p-26, x < 0 */
73		z = 0.0;
74	else
75		z = atanf(fabsf(y/x));
76	switch (m) {
77	case 0: return z;              /* atan(+,+) */
78	case 1: return -z;             /* atan(-,+) */
79	case 2: return pi - (z-pi_lo); /* atan(+,-) */
80	default: /* case 3 */
81		return (z-pi_lo) - pi; /* atan(-,-) */
82	}
83}
84