encpic.c

用c语言编写用于数据压缩的源程序

/* ENCPIC.C - MAIN PROGRAM FOR ENCODING PICTURES. */

#include <stdio.h>

#define global 

#include "code.h"

#define Height 40			/* Height of images                 */
#define Width 40                        /* Width of images                  */

static int image[Height][Width];	/* The image to be encoded          */

static int freq0[2][2];			/* Frequencies of '0' in contexts   */
static int freq1[2][2];			/* Frequencies of '1' in contexts   */

static int inc[2][2];			/* Current increment                */

void main(void)
{   
    int i, j, a, l, ch;

    start_outputing_bits();
    start_encoding();

    /* Read image. */

    for (i = 0; i<Height; i++) {
        for (j = 0; j<Width; j++) {
            do {
                ch = getc(stdin);		/* Read the next character, */
            } while (ch=='\n' || ch==' ');      /* ignoring whitespace.     */
            if (ch!='.' && ch!='#') {           /* Check for bad character. */
                fprintf(stderr,"Bad image file\n");
                exit(-1);
            }
            image[i][j] = ch=='#';		/* Convert char to pixel.   */
        }
    }

    /* Initialize model. */

    for (a = 0; a<2; a++) {
        for (l = 0; l<2; l++) {
            inc[a][l] = Freq_half;
            freq0[a][l] = inc[a][l];		/* Set frequencies of 0's   */
            freq1[a][l] = inc[a][l];		/* and 1's to be equal.     */
        }
    }

    /* Encode image. */

    for (i = 0; i<Height; i++) {
        for (j = 0; j<Width; j++) {
            a = i==0 ? 0 : image[i-1][j];	/* Find current context.    */
            l = j==0 ? 0 : image[i][j-1];
            encode_bit(image[i][j],             /* Encode pixel.            */
                       freq0[a][l],freq1[a][l]);
            if (image[i][j]) {			/* Update frequencies for   */
                freq1[a][l] += inc[a][l];       /* this context.            */
            }
            else {
                freq0[a][l] += inc[a][l];
            }
            if (freq0[a][l]+freq1[a][l]>Freq_full) { 
                freq0[a][l] = (freq0[a][l]+1) >> 1; 
                freq1[a][l] = (freq1[a][l]+1) >> 1;
                if (inc[a][l]>1) inc[a][l] >>= 1;
            }
        }
    }

    done_encoding();				/* Send the last few bits.  */
    done_outputing_bits();

    exit(0);
}