/*  
 *  MNIST Data file from http://yann.lecun.com/exdb/mnist/
 *  2006.10.25 A.Date 
 */

#include <stdio.h>
#include <stdlib.h> // exit()
#include <fcntl.h>

#define IMAGE_FILE "train-images-idx3-ubyte"
#define NUM_IMAGES 60000
#define SIZE 784   /* 28 x 28 */

static int num[10];
static unsigned char image[NUM_IMAGES][SIZE];

/*
TRAINING SET IMAGE FILE (train-images-idx3-ubyte):
[offset] [type]          [value]          [description]
0000     32 bit integer  0x00000803(2051) magic number
0004     32 bit integer  60000            number of images
0008     32 bit integer  28               number of rows
0012     32 bit integer  28               number of columns
0016     unsigned byte   ??               pixel
0017     unsigned byte   ??               pixel
........
====     unsigned byte   ??               pixel

Pixels are organized row-wise. Pixel values are 0 to 255. 0 means background (white), 255 means foreground (black). 
*/


/* http://www.kk.iij4u.or.jp/~kondo/wave/swab.html */
void FlipLong(unsigned char * ptr) {
    register unsigned char val;
    
    /* Swap 1st and 4th bytes */
    val = *(ptr);
    *(ptr) = *(ptr+3);
    *(ptr+3) = val;
    
    /* Swap 2nd and 3rd bytes */
    ptr += 1;
    val = *(ptr);
    *(ptr) = *(ptr+1);
    *(ptr+1) = val;
}


/*  Read the training images into memory */
void read_images(){

    int i, j,k, fd;
    char image_name[80];
    float f;
    unsigned char *ptr; 
    
    if ((fd=open(IMAGE_FILE,O_RDONLY))==-1){
        printf("couldn't open image file");
        exit(0);
    }
    
    read(fd,num, 4*sizeof(int) ); 
    
    for (i=0; i<4; i++) { 
	ptr  = (unsigned char *)(num + i);
	FlipLong( ptr);
	printf("%d\n", num[i]);
	ptr = ptr + sizeof(int);
    }
    
    for (i=0; i<NUM_IMAGES; i++) { 
  	read(fd,image[i], SIZE*sizeof(unsigned char) ); 
    }
    close(fd);
}


void print_images(){

    int i, j;

    for (i=0; i<NUM_IMAGES; i++) { 
	printf("#####   image %d/%d\n",i, NUM_IMAGES); 
  	for (j=0; j<SIZE; j++) { 
            printf("%3d ", image[i][j]); 
            if ( (j+1) % 28 == 0 ){
                printf("\n"); 
            }
	}
	printf("\n\n"); 
    }
    
}


int main(int argc, char **argv){
    
    read_images();
    print_images();
    
}