prime/src/Runtime/e_atan2.c

144 lines
4.0 KiB
C

/* @(#)e_atan2.c 1.2 95/01/04 */
/*
* ====================================================
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*
*/
/* __ieee754_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 "fdlibm.h"
#ifdef __STDC__
static const double
#else
static double
#endif
tiny = 1.0e-300,
zero = 0.0, pi_o_4 = 7.8539816339744827900E-01, /* 0x3FE921FB, 0x54442D18 */
pi_o_2 = 1.5707963267948965580E+00, /* 0x3FF921FB, 0x54442D18 */
pi = 3.1415926535897931160E+00, /* 0x400921FB, 0x54442D18 */
pi_lo = 1.2246467991473531772E-16; /* 0x3CA1A626, 0x33145C07 */
#ifdef __STDC__
double __ieee754_atan2(double y, double x)
#else
double __ieee754_atan2(y, x)
double y, x;
#endif
{
double z;
_INT32 k, m, hx, hy, ix, iy;
_UINT32 lx, ly;
hx = __HI(x);
ix = hx & 0x7fffffff;
lx = __LO(x);
hy = __HI(y);
iy = hy & 0x7fffffff;
ly = __LO(y);
if (((ix | ((lx | -lx) >> 31)) > 0x7ff00000) ||
((iy | ((ly | -ly) >> 31)) > 0x7ff00000)) /* x or y is NaN */
return x + y;
if ((hx - 0x3ff00000 | lx) == 0)
return atan(y); /* x=1.0 */
m = ((hy >> 31) & 1) | ((hx >> 30) & 2); /* 2*sign(x)+sign(y) */
/* when y = 0 */
if ((iy | ly) == 0) {
switch (m) {
case 0:
case 1:
return y; /* atan(+-0,+anything)=+-0 */
case 2:
return pi + tiny; /* atan(+0,-anything) = pi */
case 3:
return -pi - tiny; /* atan(-0,-anything) =-pi */
}
}
/* when x = 0 */
if ((ix | lx) == 0)
return (hy < 0) ? -pi_o_2 - tiny : pi_o_2 + tiny;
/* when x is INF */
if (ix == 0x7ff00000) {
if (iy == 0x7ff00000) {
switch (m) {
case 0:
return pi_o_4 + tiny; /* atan(+INF,+INF) */
case 1:
return -pi_o_4 - tiny; /* atan(-INF,+INF) */
case 2:
return 3.0 * pi_o_4 + tiny; /*atan(+INF,-INF)*/
case 3:
return -3.0 * pi_o_4 - tiny; /*atan(-INF,-INF)*/
}
} else {
switch (m) {
case 0:
return zero; /* atan(+...,+INF) */
case 1:
return -zero; /* atan(-...,+INF) */
case 2:
return pi + tiny; /* atan(+...,-INF) */
case 3:
return -pi - tiny; /* atan(-...,-INF) */
}
}
}
/* when y is INF */
if (iy == 0x7ff00000)
return (hy < 0) ? -pi_o_2 - tiny : pi_o_2 + tiny;
/* compute y/x */
k = (iy - ix) >> 20;
if (k > 60)
z = pi_o_2 + 0.5 * pi_lo; /* |y/x| > 2**60 */
else if (hx < 0 && k < -60)
z = 0.0; /* |y|/x < -2**60 */
else
z = atan(fabs(y / x)); /* safe to do y/x */
switch (m) {
case 0:
return z; /* atan(+,+) */
case 1:
__HI(z) ^= 0x80000000;
return z; /* atan(-,+) */
case 2:
return pi - (z - pi_lo); /* atan(+,-) */
default: /* case 3 */
return (z - pi_lo) - pi; /* atan(-,-) */
}
}