sf_cos.c

标准c库代码,可以应用于各个系统提供了大量的基本函数

/* sf_cos.c -- float version of s_cos.c.
 * Conversion to float by Ian Lance Taylor, Cygnus Support, [e-mail].
 */

/*
 * ====================================================
 * 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.
 * ====================================================
 */

#include "fdlibm.h"

#ifdef __STDC__
static const float one=1.0;
#else
static float one=1.0;
#endif

#ifdef __STDC__
	float cosf(float x)
#else
	float cosf(x)
	float x;
#endif
{
	float y[2],z=0.0;
	__int32_t n,ix;

	GET_FLOAT_WORD(ix,x);

    /* |x| ~< pi/4 */
	ix &= 0x7fffffff;
	if(ix <= 0x3f490fd8) return __kernel_cosf(x,z);

    /* cos(Inf or NaN) is NaN */
	else if (ix>=0x7f800000) return x-x;

    /* argument reduction needed */
	else {
	    n = __ieee754_rem_pio2f(x,y);
	    switch(n&3) {
		case 0: return  __kernel_cosf(y[0],y[1]);
		case 1: return -__kernel_sinf(y[0],y[1],1);
		case 2: return -__kernel_cosf(y[0],y[1]);
		default:
		        return  __kernel_sinf(y[0],y[1],1);
	    }
	}
}