blockio.c

剑桥大学David J.C. MacKay 个人网站公布的2006年的代码

/* BLOCKIO.C - Routines to read/write blocks of bits from/to a text file. */

/* Copyright (c) 2000 by Radford M. Neal 
 *
 * Permission is granted for anyone to copy, use, modify, or distribute this
 * program and accompanying programs and documents for any purpose, provided 
 * this copyright notice is retained and prominently displayed, along with
 * a note saying that the original programs are available from Radford Neal's
 * web page, and note is made of any changes made to the programs.  The
 * programs and documents are distributed without any warranty, express or
 * implied.  As the programs were written for research purposes only, they have
 * not been tested to the degree that would be advisable in any important
 * application.  All use of these programs is entirely at the user's own risk.
 */

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

#include "blockio.h"


/* READ A BLOCK OF BITS.  The bits must be given as '0' or '1' characters,
   with whitespace allowed (but not required) between bits.  Returns 0 if
   a block is read successfully, and EOF if eof or an error occurs.  If
   EOF is returned, a warning will be printed if a partial block had already
   been read. */

int blockio_read
( FILE *f,    /* File to read from */
  char *b,    /* Place to store bits read */
  int l       /* Length of block */
)
{
  int i, c;

  for (i = 0; i<l; i++)
  { 
    do
    { c = getc(f);
      if (c==EOF) 
      { if (i>0)
        { fprintf(stderr,
           "Warning: Short block (%d long) at end of input file ignored\n",i);
        }
        return EOF;
      }
    } while (c==' ' || c=='\t' || c=='\n' || c=='\r');

    if (c!='0' && c!='1')
    { fprintf(stderr,"Bad character in binary file (not '0' or '1')\n");
      exit(1);
    }

    b[i] = c=='1';
  }

  return 0;
}


/* WRITE A BLOCK OF BITS.  Bits are written as '0' and '1' characters, with
   no spaces between them, followed by a newline. */

void blockio_write
( FILE *f,     /* File to write to */
  char *b,     /* Block of bits to write */
  int l        /* Length of block */
)
{ 
  int i;

  for (i = 0; i<l; i++)
  { if (b[i]!=0 && b[i]!=1) abort();
    putc("01"[b[i]],f);
  }

  putc('\n',f);
}