update REDAME for reserve key

README.md

@@ -105,20 +105,30 @@ It's recommended to keep the default configuration for the options ending with `
 | __io_by_cpu*__             | bool   | false   | The flag indicating if the CPU handles IO.            |
 | __reserved_key_start_bit__ | int    | 0       | The start bit offset of reserved key in the 64 bit    |
 
+- Fore more details refer to [`struct HashTableOptions`](https://github.com/NVIDIA-Merlin/HierarchicalKV/blob/master/include/merlin_hashtable.cuh#L60).
+
 #### Reserved Keys
-- The keys of `0xFFFFFFFFFFFFFFFD`, `0xFFFFFFFFFFFFFFFE`, and `0xFFFFFFFFFFFFFFFF` are reserved for internal using.
-- Call set options.reserved_key_start_bit to change the reserved keys if the default one conflicted with your keys.
-  The valid range of reserved_key_start_bit is [0, 62] and the default value is 0, meaning the default reserved keys.
-  reserved_key_start_bit = 1 means using the insignificant bits 1 and 2 as the keys as the reserved keys, 
-  in binary format, it looks like 111~11xx0, and the index 0 bit is 0 and all the other bits are positive, in this case the new reserved keys are
-  `FFFFFFFFFFFFFFFE`, `0xFFFFFFFFFFFFFFFC`, `0xFFFFFFFFFFFFFFF8`, and `0xFFFFFFFFFFFFFFFA`
-  reserved_key_start_bit = 2, in binary format, it looks like 111~11xx10, bit offset 0 are always 0 for any reserved_key_start_bit != 0,
+- By default, the keys of `0xFFFFFFFFFFFFFFFD`, `0xFFFFFFFFFFFFFFFE`, and `0xFFFFFFFFFFFFFFFF` are reserved for internal using.
+  change  `options.reserved_key_start_bit` if you want to use the above keys.
+  `reserved_key_start_bit` has a valid range from 0 to 62. The default value is 0, which is the above default reserved keys. When `reserved_key_start_bit` is set to any value other than 0, the least significant bit (bit 0) is always `0` for any reserved key.
+
+- Setting `reserved_key_start_bit = 1`:
+  - This setting reserves the two least significant bits 1 and 2 for the reserved keys.
+  - In binary, the last four bits range from `1000` to `1110`. Here, the least significant bit (bit 0) is always `0`, and bits from 3 to 63 are set to `1`.
+  - The new reserved keys in hexadecimal representation are as follows:
+    - `0xFFFFFFFFFFFFFFFE`
+    - `0xFFFFFFFFFFFFFFFC`
+    - `0xFFFFFFFFFFFFFFF8`
+    - `0xFFFFFFFFFFFFFFFA`
+
+- Setting `reserved_key_start_bit = 2`:
+  - This configuration reserves bits 2 and 3 as reserved keys.
+  - The binary representation for the last five bits ranges from `10010` to `11110`, with the least significant bit (bit 0) always set to `0`, and bits from 4 to 63 are set to `1`.
+
 - if you change the reserved_key_start_bit, you should use same value for save/load
-  For more detail, please refer to [`init_reserved_keys`](https://github.com/search?q=repo%3ANVIDIA-Merlin%2FHierarchicalKV%20init_reserved_keys&type=code).
-For more detail, please refer to [`struct HashTableOptions`](https://github.com/NVIDIA-Merlin/HierarchicalKV/blob/master/include/merlin_hashtable.cuh#L60).
+  For more detail, please refer to [`init_reserved_keys`](https://github.com/search?q=repo%3ANVIDIA-Merlin%2FHierarchicalKV%20init_reserved_keys&type=code)
 
 ### How to use:
-
 ```cpp
 #include "merlin_hashtable.cuh"
 
@@ -153,6 +163,7 @@ int main(int argc, char *argv[])
 }
 
 ```
+
 ### Usage restrictions
 
 - The `key_type` must be `int64_t` or `uint64_t`.