mirror of https://github.com/PrimeDecomp/prime.git
143 lines
4.0 KiB
C
143 lines
4.0 KiB
C
/* @(#)e_atan2.c 1.2 95/01/04 */
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*
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*/
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/* __ieee754_atan2(y,x)
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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
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* constants. The decimal values may be used, provided that the
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* compiler will convert from decimal to binary accurately enough
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* to produce the hexadecimal values shown.
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*/
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#include "fdlibm.h"
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#ifdef __STDC__
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static const double
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#else
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static double
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#endif
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tiny = 1.0e-300,
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zero = 0.0, pi_o_4 = 7.8539816339744827900E-01, /* 0x3FE921FB, 0x54442D18 */
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pi_o_2 = 1.5707963267948965580E+00, /* 0x3FF921FB, 0x54442D18 */
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pi = 3.1415926535897931160E+00, /* 0x400921FB, 0x54442D18 */
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pi_lo = 1.2246467991473531772E-16; /* 0x3CA1A626, 0x33145C07 */
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#ifdef __STDC__
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double __ieee754_atan2(double y, double x)
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#else
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double __ieee754_atan2(y, x)
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double y, x;
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#endif
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{
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double z;
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_INT32 k, m, hx, hy, ix, iy; /*- cc 020130 -*/
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_UINT32 lx, ly; /*- cc 020130 -*/
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hx = __HI(x);
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ix = hx & 0x7fffffff;
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lx = __LO(x);
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hy = __HI(y);
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iy = hy & 0x7fffffff;
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ly = __LO(y);
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if (((ix | ((lx | -lx) >> 31)) > 0x7ff00000) || ((iy | ((ly | -ly) >> 31)) > 0x7ff00000)) /* x or y is NaN */
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return x + y;
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if ((hx - 0x3ff00000 | lx) == 0)
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return atan(y); /* x=1.0 */
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m = ((hy >> 31) & 1) | ((hx >> 30) & 2); /* 2*sign(x)+sign(y) */
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/* when y = 0 */
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if ((iy | ly) == 0) {
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switch (m) {
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case 0:
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case 1:
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return y; /* atan(+-0,+anything)=+-0 */
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case 2:
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return pi + tiny; /* atan(+0,-anything) = pi */
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case 3:
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return -pi - tiny; /* atan(-0,-anything) =-pi */
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}
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}
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/* when x = 0 */
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if ((ix | lx) == 0)
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return (hy < 0) ? -pi_o_2 - tiny : pi_o_2 + tiny;
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/* when x is INF */
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if (ix == 0x7ff00000) {
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if (iy == 0x7ff00000) {
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switch (m) {
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case 0:
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return pi_o_4 + tiny; /* atan(+INF,+INF) */
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case 1:
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return -pi_o_4 - tiny; /* atan(-INF,+INF) */
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case 2:
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return 3.0 * pi_o_4 + tiny; /*atan(+INF,-INF)*/
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case 3:
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return -3.0 * pi_o_4 - tiny; /*atan(-INF,-INF)*/
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}
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} else {
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switch (m) {
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case 0:
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return zero; /* atan(+...,+INF) */
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case 1:
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return -zero; /* atan(-...,+INF) */
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case 2:
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return pi + tiny; /* atan(+...,-INF) */
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case 3:
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return -pi - tiny; /* atan(-...,-INF) */
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}
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}
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}
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/* when y is INF */
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if (iy == 0x7ff00000)
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return (hy < 0) ? -pi_o_2 - tiny : pi_o_2 + tiny;
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/* compute y/x */
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k = (iy - ix) >> 20;
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if (k > 60)
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z = pi_o_2 + 0.5 * pi_lo; /* |y/x| > 2**60 */
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else if (hx < 0 && k < -60)
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z = 0.0; /* |y|/x < -2**60 */
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else
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z = atan(fabs(y / x)); /* safe to do y/x */
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switch (m) {
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case 0:
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return z; /* atan(+,+) */
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case 1:
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__HI(z) ^= 0x80000000;
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return z; /* atan(-,+) */
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case 2:
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return pi - (z - pi_lo); /* atan(+,-) */
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default: /* case 3 */
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return (z - pi_lo) - pi; /* atan(-,-) */
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}
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}
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