bounds.c

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

struct dim {
    int lower;
    int upper;
};

struct array {
    
    struct dim one, two;
    int*   buffer;
    int**   index;
    int    offset;
    
};

int pos(struct array a, int i, int j) {
    
    int rc=  a.offset
          + ( (1 + a.two.upper - a.two.lower) * (i) )
          + j ;
    
    return rc;
    
};

int cell(struct array a, int i, int j) {
    
    return * (a.buffer+pos(a,i,j));
    
};

void allocate( struct array *a ) {
    
    int size1=(1 + a->one.upper - a->one.lower) ;
    int size2=(1 + a->two.upper - a->two.lower) ;
    int size = size1 * size2  ;
    
    a->buffer=malloc(size*sizeof(int));
    

    a->offset = ( 0 - a->one.lower ) * ( size2 )
              + ( 0 - a->two.lower ) ;
    
    //initialize & print
    printf("                           Initialized\n");
    int pos=1;
    int *p=(int *) a->buffer;
    
    for ( int i=0;i<size1;i++) {
        for (int j=0;j<size2;j++){
            *p = pos ;
            printf(" %d, ", *p );
            p++;
            pos++;
        }
    }
    printf("\n");
    
}


int** create_index(struct array *a ) {
    
    int size1=(1 + a->one.upper - a->one.lower) ;
    int size2=(1 + a->two.upper - a->two.lower) ;
    
    a->index=malloc( size1 * sizeof( size_t ) );
    for (int i=0; i<size1; i++) {
        a->index[i]= a->buffer + i * size2 - a->two.lower;
    }//for
    
    a->index = a->index - a->one.lower ;
    
    return a->index;
    
}//

void bounds(){
    
    
    int i,j;
    
    struct array a={ {-3,3}, {-2,2}, NULL , NULL, 0  };
    allocate(&a);
    
    printf("                           Allocated\n");
    for ( i = -3 ; i <= +3 ; i++ ) {
        for ( j = -2 ; j <= +2  ; j++ ) {
            printf("a[%2d][%2d]=%d\n ", i,j, cell(a,i,j) );
        }
    }
    
    int** array = create_index(&a);
    
    printf("                           Indexed\n");
    for ( i = -3 ; i <= +3 ; i++ ) {
        for ( j = -2 ; j <= +2  ; j++ ) {
            printf("a[%2d][%2d]=%d\n ", i,j, array[i][j] );
        }
    }

}//bounds

int main() {

    bounds();
    
    return 0;
}