src/libm/s_cos.c
author Ryan C. Gordon <icculus@icculus.org>
Fri, 01 May 2015 01:12:48 -0400
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checkkeys: Readded the KEYUP event test.
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/* @(#)s_cos.c 5.1 93/09/24 */
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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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#if defined(LIBM_SCCS) && !defined(lint)
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static const char rcsid[] =
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    "$NetBSD: s_cos.c,v 1.7 1995/05/10 20:47:02 jtc Exp $";
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#endif
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/* cos(x)
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 * Return cosine function of x.
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 *
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 * kernel function:
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 *	__kernel_sin		... sine function on [-pi/4,pi/4]
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 *	__kernel_cos		... cosine function on [-pi/4,pi/4]
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 *	__ieee754_rem_pio2	... argument reduction routine
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 *
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 * Method.
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 *      Let S,C and T denote the sin, cos and tan respectively on
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 *	[-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
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 *	in [-pi/4 , +pi/4], and let n = k mod 4.
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 *	We have
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 *
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 *          n        sin(x)      cos(x)        tan(x)
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 *     ----------------------------------------------------------
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 *	    0	       S	   C		 T
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 *	    1	       C	  -S		-1/T
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 *	    2	      -S	  -C		 T
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 *	    3	      -C	   S		-1/T
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 *     ----------------------------------------------------------
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 *
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 * Special cases:
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 *      Let trig be any of sin, cos, or tan.
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 *      trig(+-INF)  is NaN, with signals;
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 *      trig(NaN)    is that NaN;
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 *
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 * Accuracy:
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 *	TRIG(x) returns trig(x) nearly rounded
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 */
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#include "math_libm.h"
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#include "math_private.h"
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libm_hidden_proto(cos)
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#ifdef __STDC__
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     double cos(double x)
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#else
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     double cos(x)
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     double x;
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#endif
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{
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    double y[2], z = 0.0;
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    int32_t n, ix;
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    /* High word of x. */
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    GET_HIGH_WORD(ix, x);
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    /* |x| ~< pi/4 */
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    ix &= 0x7fffffff;
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    if (ix <= 0x3fe921fb)
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        return __kernel_cos(x, z);
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    /* cos(Inf or NaN) is NaN */
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    else if (ix >= 0x7ff00000)
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        return x - x;
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    /* argument reduction needed */
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    else {
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        n = __ieee754_rem_pio2(x, y);
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        switch (n & 3) {
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        case 0:
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            return __kernel_cos(y[0], y[1]);
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        case 1:
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            return -__kernel_sin(y[0], y[1], 1);
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        case 2:
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            return -__kernel_cos(y[0], y[1]);
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        default:
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            return __kernel_sin(y[0], y[1], 1);
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        }
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    }
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}
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libm_hidden_def(cos)