makeReallocatedBitArrayZeroPadded

enum bitCount = 8*size_t.sizeof + 1;

size_t* x = makeUninitializedBitArray!(Allocator)(bitCount);
Allocator.instance.deallocate(cast(void[])(x[0 .. wordCountOfBitCount(bitCount)]));

size_t bitCount = 1;
size_t* y = makeZeroedBitArray!(Allocator)(bitCount); // start empty
while (bitCount < 100_000)
{
    const newBitCount = bitCount*2;
    y = makeReallocatedBitArrayZeroPadded!(Allocator)(y, bitCount, newBitCount);
    bitCount = newBitCount;

    // check contents
    foreach (immutable bitIndex; 0 .. bitCount)
        assert(bt(y, bitIndex) == 0);
}
Allocator.instance.deallocate(cast(void[])(y[0 .. wordCountOfBitCount(bitCount)]));