rcode.c

用于LDPC编码译码的仿真实现。包括随机生成校验矩阵、由校验矩阵产生生成矩阵、编码、加随机噪声、译码等内容。原作者是老外

/* RCODE.C - Procedures to read parity check and generator matrices. */
//读校验矩阵和生成矩阵的程序
/* Copyright (c) 2000, 2001 by Radford M. Neal  */

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#include "alloc.h"
#include "intio.h"
#include "open.h"
#include "mod2sparse.h"
#include "mod2dense.h"
#include "rcode.h"


/* VARIABLES DECLARED IN RCODE.H.  These global variables are set to
   representations of the parity check and generator matrices by read_pchk
   and read_gen. */

mod2sparse *H;		/* Parity check matrix */

int M;			/* Number of rows in parity check matrix */
int N;			/* Number of columns in parity check matrix */
//生成矩阵的表示格式s/d/m
char type;		/* Type of generator matrix representation (s/d/m) */
//生成矩阵排列的列
int *cols;		/* Ordering of columns in generator matrix */
//生成矩阵排列的行，如果生成矩阵的格式是s
int *rows;		/* Ordering of rows in generator matrix (type 's') */

mod2sparse *L, *U;	/* Sparse LU decomposition, if type=='s' */
mod2dense *G;

		/* Dense or mixed representation of generator matrix,
			   if type=='d' or type=='m' */


/* READ PARITY CHECK MATRIX.  Sets the H, M, and N global variables.  If an
   error is encountered, a message is displayed on standard error, and the
   program is terminated. */
//读校验矩阵，设置全局变量，H、M、N
void read_pchk
( char *pchk_file
)
{
  FILE *f;

  //f = open_file_std(pchk_file,"rb");
  f = fopen(pchk_file,"rb");    //以只读的方式打开一个二进制文件
  if (f==NULL)
  { fprintf(stderr,"Can't open parity check file: %s\n",pchk_file);
    exit(1);
  }

  if (intio_read(f)!=('P'<<8)+0x80)
  { fprintf(stderr,"File %s doesn't contain a parity check matrix\n",pchk_file);
    exit(1);
  }

  H = mod2sparse_read(f);

  if (H==0)
  { fprintf(stderr,"Error reading parity check matrix from %s\n",pchk_file);
    exit(1);
  }

  M = mod2sparse_rows(H);
  N = mod2sparse_cols(H);

  fclose(f);
}


/* READ GENERATOR MATRIX.  The parity check matrix must have already been 
   read, unless the last argument is set to 1.  The generator matrix must be 
   compatible with the parity check matrix, if it has been read.  If the 
   second argument is 1, only the column ordering (the last N-M of which are 
   the indexes of the message bits) is read, into the 'cols' global variable.  
   Otherwise, everything is read, into the global variables appropriate
   to the representation.  The 'type' global variable is set to a letter
   indicating which represention is used. 

   If an error is encountered, a message is displayed on standard error,
   and the program is terminated. */
//读生成矩阵，校验矩阵必须已经读过了。生成矩阵必须与检验矩阵相匹配。如果第二个参数为1，
//只把列排序()读到全局变量cols中，否则，所有的都要读。全局变量type是用来表示生成矩阵的表示方法。
void read_gen
( char *gen_file,	/* Name of generator matrix file 存储生成矩阵的文件名*/
  int cols_only,	/* Read only column ordering?是否只读排序的列 */
  int no_pchk_file	/* No parity check file used? 是否已读过校验矩阵*/
)
{
  int M2, N2;
  FILE *f;
  int i;

//  f = open_file_std(gen_file,"rb");
  f = fopen(gen_file,"rb");   //以只读的方式打开一个二进制文件
  if (f==NULL)
  { fprintf(stderr,"Can't open generator matrix file: %s\n",gen_file);
    exit(1);     //不能打开该文件
  }  

  if (intio_read(f)!=('G'<<8)+0x80)
  { fprintf(stderr,"File %s doesn't contain a generator matrix\n",gen_file);
    exit(1);   //该文件不包含生成矩阵
  }

  if (fread (&type, 1, 1, f) != 1) goto error;   //从f中读取type的值，如出错goto error

  M2 = intio_read(f);
  N2 = intio_read(f);     //读生成矩阵的行和列

  if (feof(f) || ferror(f)) goto error;

  if (no_pchk_file)
  { M = M2;
    N = N2;
  }
  else 
  { if (M2!=M || N2!=N)
    { fprintf(stderr,
              "Generator matrix and parity-check matrix are incompatible\n");
      exit(1);
    }
  }

  cols = chk_alloc (N, sizeof *cols);
  rows = chk_alloc (M, sizeof *rows);

  for (i = 0; i<N; i++)
  { cols[i] = intio_read(f);
    if (feof(f) || ferror(f)) goto error;
  }

  if (!cols_only)
  {
    switch (type)
    {
      case 's':
      { 
        for (i = 0; i<M; i++)
        { rows[i] = intio_read(f);
          if (feof(f) || ferror(f)) goto error;
        }

        if ((L = mod2sparse_read(f)) == 0) goto error;
        if ((U = mod2sparse_read(f)) == 0) goto error;
  
        if (mod2sparse_rows(L)!=M || mod2sparse_cols(L)!=M) goto garbled;
        if (mod2sparse_rows(U)!=M || mod2sparse_cols(U)<M) goto garbled;
       
        break;
      }
/*  
      case 'd':
      {
        if ((G = mod2dense_read(f)) == 0) goto error;
  
        if (mod2dense_rows(G)!=M || mod2dense_cols(G)!=N-M) goto garbled;
  
        break;
      }
  
      case 'm':
      {
        if ((G = mod2dense_read(f)) == 0) goto error;
  
        if (mod2dense_rows(G)!=M || mod2dense_cols(G)!=M) goto garbled;
  
        break;
      }
*/  
      default: 
      { fprintf(stderr,
         "Unknown type of generator matrix in file %s\n",gen_file);
        exit(1);
      }
    }
  }
  
  fclose(f);

  return;

error:
  fprintf(stderr,"Error reading generator matrix from file %s\n",gen_file);
  exit(1);

garbled:
  fprintf(stderr,"Garbled generator matrix in file %s\n",gen_file);
  exit(1);
}