72 lines
1.7 KiB
Go
72 lines
1.7 KiB
Go
// Copyright (c) 2013, 2014 Conformal Systems LLC.
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// Use of this source code is governed by an ISC
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// license that can be found in the LICENSE file.
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package bloom
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import (
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"encoding/binary"
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)
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// The following constants are used by the MurmurHash3 algorithm.
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const (
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murmurC1 = 0xcc9e2d51
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murmurC2 = 0x1b873593
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murmurR1 = 15
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murmurR2 = 13
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murmurM = 5
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murmurN = 0xe6546b64
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)
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// MurmurHash3 implements a non-cryptographic hash function using the
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// MurmurHash3 algorithm. This implementation yields a 32-bit hash value which
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// is suitable for general hash-based lookups. The seed can be used to
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// effectively randomize the hash function. This makes it ideal for use in
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// bloom filters which need multiple independent hash functions.
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func MurmurHash3(seed uint32, data []byte) uint32 {
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dataLen := uint32(len(data))
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hash := seed
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k := uint32(0)
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numBlocks := dataLen / 4
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// Calculate the hash in 4-byte chunks.
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for i := uint32(0); i < numBlocks; i++ {
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k = binary.LittleEndian.Uint32(data[i*4:])
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k *= murmurC1
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k = (k << murmurR1) | (k >> (32 - murmurR1))
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k *= murmurC2
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hash ^= k
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hash = (hash << murmurR2) | (hash >> (32 - murmurR2))
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hash = hash*murmurM + murmurN
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}
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// Handle remaining bytes.
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tailIdx := numBlocks * 4
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k = 0
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switch dataLen & 3 {
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case 3:
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k ^= uint32(data[tailIdx+2]) << 16
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fallthrough
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case 2:
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k ^= uint32(data[tailIdx+1]) << 8
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fallthrough
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case 1:
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k ^= uint32(data[tailIdx])
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k *= murmurC1
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k = (k << murmurR1) | (k >> (32 - murmurR1))
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k *= murmurC2
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hash ^= k
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}
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// Finalization.
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hash ^= uint32(dataLen)
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hash ^= hash >> 16
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hash *= 0x85ebca6b
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hash ^= hash >> 13
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hash *= 0xc2b2ae35
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hash ^= hash >> 16
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return hash
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}
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