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Optimize CRC16 calculation (with optimization of slot decision)

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Jungtaek Lim
2014-09-18 09:33:10 +09:00
parent 167221b81a
commit 96c762b880
2 changed files with 10 additions and 8 deletions
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12
src/main/java/redis/clients/util/JedisClusterCRC16.java
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@@ -4,7 +4,7 @@ package redis.clients.util;
* CRC16 Implementation according to CCITT standard
* Polynomial : 1021 (x^16 + x^12 + x^5 + 1)
*
* @see: http://redis.io/topics/cluster-spec
* @see http://redis.io/topics/cluster-spec
* Appendix A. CRC16 reference implementation in ANSI C
*/
public class JedisClusterCRC16 {
@@ -36,22 +36,24 @@ public class JedisClusterCRC16 {
key = key.substring(s+1, e);
}
}
return getCRC16(key) % 16384;
// optimization with modulo operator with power of 2
// equivalent to getCRC16(key) % 16384
return getCRC16(key) & (16384 - 1);
}
/**
* Create a CRC16 checksum from the bytes.
* implementation is from mp911de/lettuce
* implementation is from mp911de/lettuce, modified with some more optimizations
*
* @author <a href="mailto:mpaluch@paluch.biz">Mark Paluch</a>
* @param bytes
* @return CRC16 as integer value
* @see https://github.com/xetorthio/jedis/pull/733#issuecomment-55840331
*/
public static int getCRC16(byte[] bytes) {
int crc = 0x0000;
for (byte b : bytes) {
crc = ((crc << 8) ^ LOOKUP_TABLE[((crc >> 8) ^ (b & 0xFF)) & 0xFF]) & 0xFFFF;
crc = ((crc << 8) ^ LOOKUP_TABLE[((crc >>> 8) ^ (b & 0xFF)) & 0xFF]);
}
return crc & 0xFFFF;
}