Radix sort -> sort by bit mask

r_sort.c

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

#define mask_default 1 << 3
#define len(arr) sizeof(arr) / sizeof(*arr)

void r_sort(unsigned *start, unsigned *end, unsigned mask) {
    if (start == end || !mask)
        return;

    unsigned *i = start, *j = end;
    do {
        while (i < j && ~*i & mask) ++i;
        while (i < j && *j & mask) --j;
        if (i < j)
            std::swap(*i, *j);
    } while (i < j);

    if (*i & mask) --i;
    if (~*j & mask) ++j;

    unsigned n_mask = mask >> 1;
    r_sort(start, i, n_mask);
    r_sort(j, end, n_mask);
}

int main() {
    unsigned nums[] = {6, 7, 1, 8, 3, 4, 9, 2, 5, 0};
    r_sort(nums, nums + len(nums) - 1, mask_default);

    for (int i = 0; i < len(nums); ++i)
        printf("%d ", *(nums + i));
    printf("\n");

    return 0;
}