BitRange

import core.stdc.stdlib : malloc, free;
import core.stdc.string : memset;

// initialize a bit array
enum nBytes = (100 + BitRange.bitsPerWord - 1) / 8;
size_t *bitArr = cast(size_t *)malloc(nBytes);
scope(exit) free(bitArr);
memset(bitArr, 0, nBytes);

// set some bits
bts(bitArr, 48);
bts(bitArr, 24);
bts(bitArr, 95);
bts(bitArr, 78);

enum sum = 48 + 24 + 95 + 78;

// iterate
size_t testSum;
size_t nBits;
foreach (b; BitRange(bitArr, 100))
{
    testSum += b;
    ++nBits;
}

assert(testSum == sum);
assert(nBits == 4);