An Implementation

Listing 1 is short program that test encoding of all possible numbers expressible in 31 bits. The block length is 8 items, each item is 4 bits, and there is one reserved code. The procedures encode() and decode() are compact, yet should provide some flexibility, and a starting point for your application. For more on the encode() and decode() procedures, see the source code available here.

// tst_all_nibbles.c
#include <stdint.h>
#include <assert.h>
#include <stdio.h>

#include "linked_encode_decode.h"

/* A simple test program that goes through all possible 
   permutations of a 31 bit integer. Encodes into nibbles
   where each nibble must be different from 0. Decodes
   and compares
*/

int main( void ) {
        uint32_t i = 0;
        uint32_t j;
        uint32_t arr[8];
        uint32_t original[8];
        uint32_t result;

        do {
                for ( j = 0; j < 8; j++ ) {                        
                        arr[j] = (i >> (j*4)) & 0xF;
                        original[j] = arr[j];
                }
                encode( 8, arr );
                for ( j = 0; j < 8; j++ )
                        assert( arr[j] != 0 );
                decode( arr );
                result = 0;
                for ( j = 0; j < 8; j++ )
                        result |= (arr[j] << (j*4));
                assert( result == i );

                i -= 2; // i is an uint32_t
                if ( (i & 0xFFFFFF) == 0 )
                        fprintf( stderr,"." );
        } while ( i != 0 );
        return 0;
}