#include "stdafx.h"
#include "math.h"
#include "findperi.h"

static const int samplesize=30;
static const int thredthold=800;

static double vectorangle(int size, unsigned char * a, unsigned char * b)
{
	double sa,sb,sab;
	sa=0;
	sb=0;
	sab=0;
	for(int i=0; i<size; i++){
		sa+=a[i]*a[i];
		sb+=b[i]*b[i];
		sab+=abs(a[i]*b[i]);
	}
	return sab/(sqrt(sa)*sqrt(sb));
}

int findt::matchvalue(int ib, int n)
{
	int s, k;
	s=0;
	for(int i=0; i<samplesize; i++){
		k = buffer[ib+i]-buffer[n+i];
		s+=k*k;
		if(s>thredthold)
			return s;
	}
	return s;
}

int findt::ismatch(int ib, int n)
{
	if(n+2*samplesize>buffersize)
		return 0;
	int mv,mv2;
	mv = matchvalue(ib, n);
	if(mv > thredthold)
		return 0;
	int k;
	k=0;
	while(1) {
		if(n+k+1+samplesize >= buffersize)
			return 0;
		mv2 = matchvalue(ib, n+k+1);
		if(mv2 >= mv)
			break;
		mv = mv2;
		k++;
	}
	k = n+k;
	mv = matchvalue(ib, k+(k-ib));
	if(mv > thredthold)
		return 0;
	period = k-ib;
	if(vectorangle(k-ib,buffer+ib,buffer+k)<0.9)
		return 0;
	return period;
}

static int vmax(unsigned char * buf)
{
	int smax=0;
	for(int i=0; i<samplesize; i++)
		if(smax<buf[i])
			smax = buf[i];
	return smax;
}

int findt::tryperiod(int ib)
{
	int i;
	for(i=0; i<1024; i+=512){
		if(vmax(buffer+i)<5)return 0;
		int n;
		n = ismatch(i, i+ib);
		if(n)
			return n;
	}
	return 0;
}

int findt::find()
{
	if(buffersize<1000) return 0;
	if(buffer == NULL) return 0;
	for(int i=40; i<500; i++){
		int t;
		t=tryperiod(i);
		if(t)
			return t;
	}
	return 0;
}

int findperiod(int tsize, unsigned char * buffer)
{
	findt fd(tsize, buffer);
	return fd.find();
}