make-gen.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

/* MAKE-GEN.C - Make generator matrix from parity-check matrix. */
//从校验矩阵到生成矩阵
/* Copyright (c) 2000, 2001 by Radford M. Neal 
 *
 * Permission is granted for anyone to copy, use, or modify this program 
 * for purposes of research or education, provided this copyright notice 
 * is retained, and note is made of any changes that have been made. 
 *
 * This program is distributed without any warranty, express or implied.
 * As this program was written for research purposes only, it has not been
 * tested to the degree that would be advisable in any important application.
 * All use of this program is entirely at the user's own risk.
 */

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


#include "alloc.h"
#include "intio.h"
#include "open.h"
#include "rcode.h"
#include "mod2sparse.h"
#include "make-gen.h"
//#include "mod2dense.h"
//#include "mod2convert.h"


void make_gen
(char *pchk_file,
 char *gen_file,
 mod2sparse_strategy strategy
)
{
    FILE *f;

  /* Read parity check matrix.读校验矩阵*/

  read_pchk(pchk_file);

  if (N<=M)
  { fprintf(stderr,
     "Can't encode if number of bits (%d) isn't greater than number of checks (%d)\n",N,M);
    exit(1);
  }

  /* Create generator matrix file.创建存储生成矩阵的文件 */

  f = open_file_std(gen_file,"wb");
  if (f==NULL)
  { fprintf(stderr,"Can't create generator matrix file: %s\n",gen_file);
    exit(1);
  }

  /* Allocate space for row and column permutations. */
  //为行和列的排序分配空间
  cols = chk_alloc (N, sizeof *cols);
  rows = chk_alloc (M, sizeof *rows);

  /* Create generator matrix . */
  //创建生成矩阵
  make_sparse(f,strategy); 

  /* Check for error writing file. */

  if (ferror(f) || fclose(f)!=0)
  { fprintf(stderr,"Error writing to generator matrix file\n");
    exit(1);
  }
  mod2sparse_free(H);//lxh
//  mod2sparse_free(L);//lxh
//  mod2sparse_free(U);//lxh
 free(cols); //lxh
  free(rows); //lxh
  

}

/* MAKE SPARSE REPRESENTATION OF GENERATOR MATRIX. */
//生成矩阵的稀疏矩阵表示
void make_sparse
( FILE *f,
  mod2sparse_strategy strategy
)
{
	int abandon_number =0;
	int abandon_when=1;
    int n, cL, cU, cB;
    int i;

  /* Find LU decomposition. */

  L = mod2sparse_allocate(M,M);
  U = mod2sparse_allocate(M,N);

  n = mod2sparse_decomp(H,M,rows,cols,strategy,abandon_number,abandon_when);

  if (n!=0 && abandon_number==0)
  { fprintf(stderr,"Note: Parity check matrix has %d redundant checks\n",n);
  }
  if (n!=0 && abandon_number>0)
  { fprintf(stderr,
  "Note: Have %d dependent columns, but this could be due to abandonment.\n",n);
    fprintf(stderr,
  "      Try again with lower abandonment number.\n");
    exit(1);
  }

  /* Compute and print number of 1s. */

  cL = cU = cB = 0;

  for (i = 0; i<M; i++) cL += mod2sparse_count_row(L,i);
  for (i = 0; i<M; i++) cU += mod2sparse_count_row(U,i);
  for (i = M; i<N; i++) cB += mod2sparse_count_col(H,cols[i]);

  /*fprintf(stderr,
   "Number of 1s per check in L is %.1f, U is %.1f, B is %.1f, total is %.1f\n",
    (double)cU/M, (double)cL/M, (double)cB/M, (double)(cL+cU+cB)/M);*/

  /* Write it all to the generator matrix file. */

  intio_write(f,('G'<<8)+0x80);

  fwrite ("s", 1, 1, f);

  intio_write(f,M);
  intio_write(f,N);

  for (i = 0; i<N; i++) 
  { intio_write(f,cols[i]);
  }

  for (i = 0; i<M; i++) 
  { intio_write(f,rows[i]);
  }

  mod2sparse_write (f, L);
  mod2sparse_write (f, U);
  mod2sparse_free(L);//lxh
  mod2sparse_free(U);//lxh
}


/* PRINT USAGE MESSAGE AND EXIT. */

void gen_usage(void)
{ fprintf (stderr, 
   "Usage:  make-gen pchk-file gen-file method\n");
  fprintf (stderr, 
   "Method: sparse [ \"first\" | \"mincol\" | \"minprod\" ] [ abandon_num abandon_when ]\n");
  fprintf (stderr, 
   "    or: dense [ other-gen-file ]\n");
  fprintf (stderr, 
   "    or: mixed [ other-gen-file ]\n");
  exit(1);
}