BITCOUNTCount set bits in a string, optionally over a byte range.
| Syntax | BITCOUNT key [start end] |
| Group | string |
| Arity | -2 |
| Since | 1.0.0 |
| Flags | readonly |
| Complexity | O(N) over the counted bytes |
| Redis compatibility | differs: the BYTE / BIT unit argument of Redis 7.0 is not accepted — ranges are byte offsets |