Experiments with an LSD Radix sort

sort.c

#include <stdlib.h> /* malloc, free */
#include <stdio.h> /* NULL */

/**
 * Stably sort and array of unsigned integers in place in linear time. Uses
 * linear extra space. Return 0 on failure to allocate memory and 1 on success.
 *
 * Author: William Schwartz
 */
int sort(unsigned int a[], size_t len) {
	if (len < 2)
		return 1;
	size_t zero = 0, one = 0, i;
	unsigned int ai, d;
	unsigned int *aux = (unsigned int *) malloc(len * sizeof(unsigned int));
	if (aux == NULL)
		return 0;
	for (d = 1; d; d <<= 1) {
		for (i = 0; i < len; one += a[i++] & d)
		for (i = 0; i < len; i++) {
	  		ai = a[i];
	  		if (ai & d) aux[one++ ] = ai;
		  	else        aux[zero++] = ai;
		}
		for (i = 0; i < len; a[i] = aux[i++])
	}
	free(aux);
	return 1;
}

Something is quite wrong with one += a[i++] & d.