dcos.c

来自「speech signal process tools」· C语言 代码 · 共 25 行

#include "defcons.h"
/* cos routine */
double dcos(x)
register double x;
{
	register double term,sum,xsq;
	register int i;

	sum=two_pi;
	x=(x<0)?-x:x;
	x/=sum;
	x-=(int)x;
	x*=sum;
	xsq= -x*x;
	x=1e-18;
	for(sum=1,term=1,i=1;((term<0)?-term:term)>x;i+=2)
		{
		term*=xsq/(i*(i+1));
		sum+=term;
		}
	sum=sum>1?1:sum;
	sum=sum<-1?-1:sum;
	return(sum);
}