decode.cpp

低密度奇偶校验码decode的c实现程序,不错

#include "LDPC_head.h"
#include <stdlib.h>


struct code *initializtion(struct code *codewords,double n0);
void one_step(struct matrix_bit *matrix, struct node *head,struct code *f);
double basic(double x,double y);
struct code *judge(struct node *head,struct code *codewords,struct code *f);

unsigned int decode(struct code *codeword,struct matrix_bit *matrix,struct node *head1, unsigned int *message,double n0)
{
	code	*codewords;
	code    *final_code;
	
	code	*f;
	node	*head;
	node	*p1;
//	node	*p2;
	unsigned int i;
	unsigned int j;
	unsigned int k;

	head=head1;
	codewords=codeword;

	//calculate the LLRs of every bit   
	f=initializtion(codewords,n0);

	for(i=0;i<matrix->N;i++)
	{
		p1=head->right+i;
		p1->Q=f->codeword[i];
		p1->R=0;
		p1=p1->down;
		while(p1->row!=-1)
		{
			p1->Q=f->codeword[i];
			p1->R=0;
			p1=p1->down;
		}
	}


	for(i=0;i<iterative_num;i++)
	{
    //	cout<<i<<endl;
		one_step(matrix,head,f);
	//	cout<<i<<endl;
        final_code=judge(head,codewords,f);
		j=0;
		for(k=0;k<matrix->M1;k++)
		{
			if(message[k]!=(unsigned int)final_code->codeword[k])
			{
				j++;
			}
		}
		free(final_code->codeword);
		free(final_code);
		if(j==0)
		{
			break;
		}
	}
	
	free(f->codeword);
	free(f);	
	return (j);

}

//calculate the LLRs of every bit   
code *initializtion(struct code *codewords,double n0)
{
	unsigned int i;
	code *f;

	f=(struct code *) malloc (sizeof(struct code));
	f->length=codewords->length;
	f->codeword=(double *) malloc ((sizeof(double))*f->length);

	for(i=0;i<f->length;i++)
	{
    //  when LLRs decoding
		f->codeword[i]=4*codewords->codeword[i]/n0;
	//  when LRs decoding
	//	f->codeword[i]=exp(-4*(codewords->codeword[i])/n0);
	}
	return (f);
}

double basic(double x,double y)
{
//  when LLRs decoding
	double z;
	z=log((1+exp(x+y))/(exp(x)+exp(y)));
	//overlow?
	if(z>MAX)
	{
		z=MAX;
	}
	else if(z<-MAX)
	{
		z=-MAX;
	}
	return z;

//  when LRs decoding
/*	double z;
	z=(x+y)/(1+x*y);
	if(z>MAX)
	{
		z=MAX;
	}
	return z;
*/
}


void one_step(struct matrix_bit *matrix, struct node *head,struct code *f)
{
//  when LLRs decoding
	double temp;
	node *p1;
	node *p2;


	//horizontal step;
	p1=head->down;
	while(p1->row!=-1)
	{
		p2=p1->right;
		temp=p2->Q;
		p2=p2->right;
		while(p2->col!=-1)
		{
			p2->R=temp;
			temp=basic(temp,p2->Q);
			p2=p2->right;
		}
		p2=p1->left;
		temp=p2->Q;
		p2=p2->left;
        
		while(p2->left->col!=-1)
		{
			p2->R=basic(p2->R, temp);
			temp=basic(temp, p2->Q);
			p2=p2->left;
				
		}
		p2->R=temp;
	
		p1=p1->down;
	}
	

	//vertical step
    p1=head->right;
	
	while(p1->col!=-1)
	{
		p2=p1->down;
		temp=f->codeword[p2->col];
		while(p2->row!=-1)
		{
			p2->Q=temp;
			temp+=p2->R;
			p2=p2->down;
		}
	
		p2=p1->up;
		temp=p2->R;
		p2=p2->up;
		while(p2->row!=-1)
		{
			p2->Q+=temp;
			temp+=p2->R;
			p2=p2->up;
		}

		p1=p1->right;
	}


//  when LRs decoding
/*
	double temp;
	node *p1;
	node *p2;

	//horizontal step;
	p1=head->down;
	while(p1->row!=-1)
	{
		p2=p1->right;
		temp=0;
		while(p2->col!=-1)
		{
			p2->R=temp;
			temp=basic(temp,p2->Q);
			p2=p2->right;
		}
		p2=p1->left;
		temp=0;
		while(p2->col!=-1)
		{
			p2->R=basic(p2->R, temp);
			temp=basic(temp, p2->Q);
			p2=p2->left;
		}
		p1=p1->down;
	}

	//vertical step
	p1=head->right;
	while(p1->col!=-1)
	{
		p2=p1->down;
		temp=f->codeword[p2->col];
		while(p2->row!=-1)
		{
			p2->Q=temp;
			temp*=p2->R;
			if(temp>MAX)
			{
				temp=MAX;
			}
			p2=p2->down;
		}

		p2=p1->up;
		temp=1;
		while(p2->row!=-1)
		{
			p2->Q*=temp;
			temp*=p2->R;
			if(temp>MAX)
			{
				temp=MAX;
			}
			p2=p2->up;
		}
		p1=p1->right;
	}
	*/
}

code *judge(struct node *head,struct code *codewords,struct code *f)
{
// when LLRs decoding
	int i;
	node *p;
	code *final_code;

	final_code=(struct code *)malloc(sizeof(struct code));
	final_code->length=codewords->length;
	final_code->codeword=(double *)malloc((sizeof(double))*final_code->length);
	p=head->right;
	i=0;

	while(p->col!=-1)
	{
        if((p->down->Q+p->down->R)>0)
		{
		    final_code->codeword[i]=0;
		}
		else
		{
			final_code->codeword[i]=1;
		}
		p=p->right;
		i++;
	}
	return(final_code);



//  when LRs decoding
/*
	int i;
	node *p;
	code *final_code;

	final_code=(struct code *)malloc(sizeof(struct code));
	final_code->length=codewords->length;
	final_code->codeword=(double *)malloc((sizeof(double))*final_code->length);
	p=head->right;
	i=0;
	while(p->col!=-1)
	{
		if(p->down->Q*p->down->R>1)
		{
			final_code->codeword[i]=1;
		}else
		{
			final_code->codeword[i]=0;
		}
		p=p->right;
		i++;
	}
	return(final_code);
*/

}