| /* origin: FreeBSD /usr/src/lib/msun/src/s_cos.c */ |
| /* |
| * ==================================================== |
| * 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. |
| * ==================================================== |
| */ |
| /* cos(x) |
| * Return cosine function of x. |
| * |
| * kernel function: |
| * __sin ... sine function on [-pi/4,pi/4] |
| * __cos ... cosine function on [-pi/4,pi/4] |
| * __rem_pio2 ... argument reduction routine |
| * |
| * Method. |
| * Let S,C and T denote the sin, cos and tan respectively on |
| * [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2 |
| * in [-pi/4 , +pi/4], and let n = k mod 4. |
| * We have |
| * |
| * n sin(x) cos(x) tan(x) |
| * ---------------------------------------------------------- |
| * 0 S C T |
| * 1 C -S -1/T |
| * 2 -S -C T |
| * 3 -C S -1/T |
| * ---------------------------------------------------------- |
| * |
| * Special cases: |
| * Let trig be any of sin, cos, or tan. |
| * trig(+-INF) is NaN, with signals; |
| * trig(NaN) is that NaN; |
| * |
| * Accuracy: |
| * TRIG(x) returns trig(x) nearly rounded |
| */ |
| |
| #include "libm.h" |
| |
| double cos(double x) |
| { |
| double y[2]; |
| uint32_t ix; |
| unsigned n; |
| |
| GET_HIGH_WORD(ix, x); |
| ix &= 0x7fffffff; |
| |
| /* |x| ~< pi/4 */ |
| if (ix <= 0x3fe921fb) { |
| if (ix < 0x3e46a09e) { /* |x| < 2**-27 * sqrt(2) */ |
| /* raise inexact if x!=0 */ |
| FORCE_EVAL(x + 0x1p120f); |
| return 1.0; |
| } |
| return __cos(x, 0); |
| } |
| |
| /* cos(Inf or NaN) is NaN */ |
| if (ix >= 0x7ff00000) |
| return x-x; |
| |
| /* argument reduction */ |
| n = __rem_pio2(x, y); |
| switch (n&3) { |
| case 0: return __cos(y[0], y[1]); |
| case 1: return -__sin(y[0], y[1], 1); |
| case 2: return -__cos(y[0], y[1]); |
| default: |
| return __sin(y[0], y[1], 1); |
| } |
| } |
