Function mi_bitmap_popcountN

system/lib/mimalloc/src/bitmap.c:1150–1172

Count bits set in a range of `n` bits.

// Count bits set in a range of `n` bits.
size_t mi_bitmap_popcountN( mi_bitmap_t* bitmap, size_t idx, size_t n) {
  mi_assert_internal(n>0);
  const size_t maxbits = mi_bitmap_max_bits(bitmap);
  mi_assert_internal(idx + n <= maxbits);
  if (idx+n > maxbits) { // paranoia
    if (idx >= maxbits) return 0;
    n = maxbits - idx;
  }

  // iterate through the chunks
  size_t chunk_idx = idx / MI_BCHUNK_BITS;
  size_t cidx = idx % MI_BCHUNK_BITS;
  size_t popcount = 0;
  while (n > 0) {
    const size_t m = (cidx + n > MI_BCHUNK_BITS ? MI_BCHUNK_BITS - cidx : n);
    popcount += mi_bchunk_popcountN(&bitmap->chunks[chunk_idx], cidx, m);
    mi_assert_internal(m <= n);
    n -= m;
    cidx = 0;
    chunk_idx++;
  }
  return popcount;
}


// Set/clear a bit in the bitmap; returns `true` if atomically transitioned from 0 to 1 (or 1 to 0)