急！那位大侠有用C语言实现的互相关算法的源代码，谢谢啦

#include <math.h>
#define M_PI 3.14159265358979323846
#define FALSE 0
#define TRUE 1
#define BIG 1e10
#define SMALL 1e-10

typedef struct {
float r, i;
} complex;

/* FAST CORRELATION OF X(0:L) AND Y(0:L). FINDS RXY(0) THRU RXY(NMAX). */
/* L=LAST INDEX IN BOTH X AND Y. MUST BE (POWER OF 2)+1 AND AT LEAST 5. */
/* ITYPE=TYPE OF CORRELATION=0 IF X AND Y ARE THE SAME VECTOR (AUTO- */
/* CORRELATION), OR NOT 0 IF X AND Y ARE DIFFERENT VECTORS. */
/* NMAX=MAXIMUM LAG OF INTEREST IN THE CORRELATION FUNCTION. */
/* FFT LENGTH ,N, USED INTERNALLY, IS L-1. */
/* LET K=INDEX OF FIRST NONZERO SAMPLE IN Y(0)---Y(N-1). THEN X(0) */
/* 到 X(N-1) MUST INCLUDE PADDING OF AT LEAST NMAX-K ZEROS. */
/* CORRELATION FUNCTION, RXY, REPLACES X(0) THRU X(NMAX). */
/* Y(0) THRU Y(L) IS REPLACED BY ITS FFT, COMPUTED USING SPFFTR. */
/* IERROR=0 NO ERROR DETECTED */