BITCOUNTCount set bits in a string, optionally over a byte range.
| 语法 | BITCOUNT key [start end] |
| 分组 | string |
| 参数个数 | -2 |
| 起始版本 | 1.0.0 |
| 标志 | readonly |
| 复杂度 | O(N) over the counted bytes |
| Redis 兼容性 | differs: the BYTE / BIT unit argument of Redis 7.0 is not accepted — ranges are byte offsets |