| 1 | package net.spy.memcached; |
| 2 | |
| 3 | import java.security.MessageDigest; |
| 4 | import java.security.NoSuchAlgorithmException; |
| 5 | import java.util.zip.CRC32; |
| 6 | |
| 7 | /** |
| 8 | * Known hashing algorithms for locating a server for a key. |
| 9 | * Note that all hash algorithms return 64-bits of hash, but only the lower |
| 10 | * 32-bits are significant. This allows a positive 32-bit number to be |
| 11 | * returned for all cases. |
| 12 | */ |
| 13 | public enum HashAlgorithm { |
| 14 | |
| 15 | /** |
| 16 | * Native hash (String.hashCode()). |
| 17 | */ |
| 18 | NATIVE_HASH, |
| 19 | /** |
| 20 | * CRC32_HASH as used by the perl API. This will be more consistent both |
| 21 | * across multiple API users as well as java versions, but is mostly likely |
| 22 | * significantly slower. |
| 23 | */ |
| 24 | CRC32_HASH, |
| 25 | /** |
| 26 | * FNV hashes are designed to be fast while maintaining a low collision |
| 27 | * rate. The FNV speed allows one to quickly hash lots of data while |
| 28 | * maintaining a reasonable collision rate. |
| 29 | * |
| 30 | * @see <a href="http://www.isthe.com/chongo/tech/comp/fnv/">fnv comparisons</a> |
| 31 | * @see <a href="http://en.wikipedia.org/wiki/Fowler_Noll_Vo_hash">fnv at wikipedia</a> |
| 32 | */ |
| 33 | FNV1_64_HASH, |
| 34 | /** |
| 35 | * Variation of FNV. |
| 36 | */ |
| 37 | FNV1A_64_HASH, |
| 38 | /** |
| 39 | * 32-bit FNV1. |
| 40 | */ |
| 41 | FNV1_32_HASH, |
| 42 | /** |
| 43 | * 32-bit FNV1a. |
| 44 | */ |
| 45 | FNV1A_32_HASH, |
| 46 | /** |
| 47 | * MD5-based hash algorithm used by ketama. |
| 48 | */ |
| 49 | KETAMA_HASH; |
| 50 | |
| 51 | private static final long FNV_64_INIT = 0xcbf29ce484222325L; |
| 52 | private static final long FNV_64_PRIME = 0x100000001b3L; |
| 53 | |
| 54 | private static final long FNV_32_INIT = 2166136261L; |
| 55 | private static final long FNV_32_PRIME = 16777619; |
| 56 | |
| 57 | /** |
| 58 | * Compute the hash for the given key. |
| 59 | * |
| 60 | * @return a positive integer hash |
| 61 | */ |
| 62 | public long hash(final String k) { |
| 63 | long rv = 0; |
| 64 | switch (this) { |
| 65 | case NATIVE_HASH: |
| 66 | rv = k.hashCode(); |
| 67 | break; |
| 68 | case CRC32_HASH: |
| 69 | // return (crc32(shift) >> 16) & 0x7fff; |
| 70 | CRC32 crc32 = new CRC32(); |
| 71 | crc32.update(KeyUtil.getKeyBytes(k)); |
| 72 | rv = (crc32.getValue() >> 16) & 0x7fff; |
| 73 | break; |
| 74 | case FNV1_64_HASH: { |
| 75 | // Thanks to pierre@demartines.com for the pointer |
| 76 | rv = FNV_64_INIT; |
| 77 | int len = k.length(); |
| 78 | for (int i = 0; i < len; i++) { |
| 79 | rv *= FNV_64_PRIME; |
| 80 | rv ^= k.charAt(i); |
| 81 | } |
| 82 | } |
| 83 | break; |
| 84 | case FNV1A_64_HASH: { |
| 85 | rv = FNV_64_INIT; |
| 86 | int len = k.length(); |
| 87 | for (int i = 0; i < len; i++) { |
| 88 | rv ^= k.charAt(i); |
| 89 | rv *= FNV_64_PRIME; |
| 90 | } |
| 91 | } |
| 92 | break; |
| 93 | case FNV1_32_HASH: { |
| 94 | rv = FNV_32_INIT; |
| 95 | int len = k.length(); |
| 96 | for (int i = 0; i < len; i++) { |
| 97 | rv *= FNV_32_PRIME; |
| 98 | rv ^= k.charAt(i); |
| 99 | } |
| 100 | } |
| 101 | break; |
| 102 | case FNV1A_32_HASH: { |
| 103 | rv = FNV_32_INIT; |
| 104 | int len = k.length(); |
| 105 | for (int i = 0; i < len; i++) { |
| 106 | rv ^= k.charAt(i); |
| 107 | rv *= FNV_32_PRIME; |
| 108 | } |
| 109 | } |
| 110 | break; |
| 111 | case KETAMA_HASH: |
| 112 | byte[] bKey=computeMd5(k); |
| 113 | rv = ((long) (bKey[3] & 0xFF) << 24) |
| 114 | | ((long) (bKey[2] & 0xFF) << 16) |
| 115 | | ((long) (bKey[1] & 0xFF) << 8) |
| 116 | | (bKey[0] & 0xFF); |
| 117 | break; |
| 118 | default: |
| 119 | assert false; |
| 120 | } |
| 121 | return rv & 0xffffffffL; /* Truncate to 32-bits */ |
| 122 | } |
| 123 | |
| 124 | /** |
| 125 | * Get the md5 of the given key. |
| 126 | */ |
| 127 | public static byte[] computeMd5(String k) { |
| 128 | MessageDigest md5; |
| 129 | try { |
| 130 | md5 = MessageDigest.getInstance("MD5"); |
| 131 | } catch (NoSuchAlgorithmException e) { |
| 132 | throw new RuntimeException("MD5 not supported", e); |
| 133 | } |
| 134 | md5.reset(); |
| 135 | md5.update(KeyUtil.getKeyBytes(k)); |
| 136 | return md5.digest(); |
| 137 | } |
| 138 | } |