1*f504f610SAugustin Cavalier /* origin: FreeBSD /usr/src/lib/msun/src/e_atan2f.c */
2*f504f610SAugustin Cavalier /*
3*f504f610SAugustin Cavalier * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
4*f504f610SAugustin Cavalier */
5*f504f610SAugustin Cavalier /*
6*f504f610SAugustin Cavalier * ====================================================
7*f504f610SAugustin Cavalier * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
8*f504f610SAugustin Cavalier *
9*f504f610SAugustin Cavalier * Developed at SunPro, a Sun Microsystems, Inc. business.
10*f504f610SAugustin Cavalier * Permission to use, copy, modify, and distribute this
11*f504f610SAugustin Cavalier * software is freely granted, provided that this notice
12*f504f610SAugustin Cavalier * is preserved.
13*f504f610SAugustin Cavalier * ====================================================
14*f504f610SAugustin Cavalier */
15*f504f610SAugustin Cavalier
16*f504f610SAugustin Cavalier #include "libm.h"
17*f504f610SAugustin Cavalier
18*f504f610SAugustin Cavalier static const float
19*f504f610SAugustin Cavalier pi = 3.1415927410e+00, /* 0x40490fdb */
20*f504f610SAugustin Cavalier pi_lo = -8.7422776573e-08; /* 0xb3bbbd2e */
21*f504f610SAugustin Cavalier
atan2f(float y,float x)22*f504f610SAugustin Cavalier float atan2f(float y, float x)
23*f504f610SAugustin Cavalier {
24*f504f610SAugustin Cavalier float z;
25*f504f610SAugustin Cavalier uint32_t m,ix,iy;
26*f504f610SAugustin Cavalier
27*f504f610SAugustin Cavalier if (isnan(x) || isnan(y))
28*f504f610SAugustin Cavalier return x+y;
29*f504f610SAugustin Cavalier GET_FLOAT_WORD(ix, x);
30*f504f610SAugustin Cavalier GET_FLOAT_WORD(iy, y);
31*f504f610SAugustin Cavalier if (ix == 0x3f800000) /* x=1.0 */
32*f504f610SAugustin Cavalier return atanf(y);
33*f504f610SAugustin Cavalier m = ((iy>>31)&1) | ((ix>>30)&2); /* 2*sign(x)+sign(y) */
34*f504f610SAugustin Cavalier ix &= 0x7fffffff;
35*f504f610SAugustin Cavalier iy &= 0x7fffffff;
36*f504f610SAugustin Cavalier
37*f504f610SAugustin Cavalier /* when y = 0 */
38*f504f610SAugustin Cavalier if (iy == 0) {
39*f504f610SAugustin Cavalier switch (m) {
40*f504f610SAugustin Cavalier case 0:
41*f504f610SAugustin Cavalier case 1: return y; /* atan(+-0,+anything)=+-0 */
42*f504f610SAugustin Cavalier case 2: return pi; /* atan(+0,-anything) = pi */
43*f504f610SAugustin Cavalier case 3: return -pi; /* atan(-0,-anything) =-pi */
44*f504f610SAugustin Cavalier }
45*f504f610SAugustin Cavalier }
46*f504f610SAugustin Cavalier /* when x = 0 */
47*f504f610SAugustin Cavalier if (ix == 0)
48*f504f610SAugustin Cavalier return m&1 ? -pi/2 : pi/2;
49*f504f610SAugustin Cavalier /* when x is INF */
50*f504f610SAugustin Cavalier if (ix == 0x7f800000) {
51*f504f610SAugustin Cavalier if (iy == 0x7f800000) {
52*f504f610SAugustin Cavalier switch (m) {
53*f504f610SAugustin Cavalier case 0: return pi/4; /* atan(+INF,+INF) */
54*f504f610SAugustin Cavalier case 1: return -pi/4; /* atan(-INF,+INF) */
55*f504f610SAugustin Cavalier case 2: return 3*pi/4; /*atan(+INF,-INF)*/
56*f504f610SAugustin Cavalier case 3: return -3*pi/4; /*atan(-INF,-INF)*/
57*f504f610SAugustin Cavalier }
58*f504f610SAugustin Cavalier } else {
59*f504f610SAugustin Cavalier switch (m) {
60*f504f610SAugustin Cavalier case 0: return 0.0f; /* atan(+...,+INF) */
61*f504f610SAugustin Cavalier case 1: return -0.0f; /* atan(-...,+INF) */
62*f504f610SAugustin Cavalier case 2: return pi; /* atan(+...,-INF) */
63*f504f610SAugustin Cavalier case 3: return -pi; /* atan(-...,-INF) */
64*f504f610SAugustin Cavalier }
65*f504f610SAugustin Cavalier }
66*f504f610SAugustin Cavalier }
67*f504f610SAugustin Cavalier /* |y/x| > 0x1p26 */
68*f504f610SAugustin Cavalier if (ix+(26<<23) < iy || iy == 0x7f800000)
69*f504f610SAugustin Cavalier return m&1 ? -pi/2 : pi/2;
70*f504f610SAugustin Cavalier
71*f504f610SAugustin Cavalier /* z = atan(|y/x|) with correct underflow */
72*f504f610SAugustin Cavalier if ((m&2) && iy+(26<<23) < ix) /*|y/x| < 0x1p-26, x < 0 */
73*f504f610SAugustin Cavalier z = 0.0;
74*f504f610SAugustin Cavalier else
75*f504f610SAugustin Cavalier z = atanf(fabsf(y/x));
76*f504f610SAugustin Cavalier switch (m) {
77*f504f610SAugustin Cavalier case 0: return z; /* atan(+,+) */
78*f504f610SAugustin Cavalier case 1: return -z; /* atan(-,+) */
79*f504f610SAugustin Cavalier case 2: return pi - (z-pi_lo); /* atan(+,-) */
80*f504f610SAugustin Cavalier default: /* case 3 */
81*f504f610SAugustin Cavalier return (z-pi_lo) - pi; /* atan(-,-) */
82*f504f610SAugustin Cavalier }
83*f504f610SAugustin Cavalier }
84