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MurmurHash v3 for bucketing (#4)
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‎src/main/kotlin/com/featurevisor/sdk/Bucket.kt

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package com.featurevisor.sdk
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object Bucket {
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private const val HASH_SEED = 1
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private const val MAX_HASH_VALUE = 4294967296 // 2^32
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// 100% * 1000 to include three decimal places in the same integer value
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private const val MAX_BUCKETED_NUMBER = 100000
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fun getBucketedNumber(bucketKey: String): Int {
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val hashValue = MurmurHash3().hash32x86(bucketKey.toByteArray())
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val ratio = hashValue.toDouble() / MAX_HASH_VALUE
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return kotlin.math.floor(ratio * MAX_BUCKETED_NUMBER).toInt()
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}
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}

‎src/main/kotlin/com/featurevisor/sdk/MurmurHash3.kt

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package com.featurevisor.sdk
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/**
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* Taken from: https://github.com/goncalossilva/kotlinx-murmurhash
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*
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* (Copied to make it work, we can resort to using it as a package later)
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*
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* ---
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*
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* MIT License
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*
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* Copyright (c) 2021-2022 Gonçalo Silva
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
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* associated documentation files (the "Software"), to deal in the Software without restriction,
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* including without limitation the rights to use, copy, modify, merge, publish, distribute,
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* sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all copies or
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* substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
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* NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
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* DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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public class MurmurHash3(private val seed: UInt = 1.toUInt()) {
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public fun hash32x86(key: ByteArray): UInt {
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var h = seed
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val len = key.size
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val nblocks = len / 4
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for (i in 0 until nblocks * 4 step 4) {
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val k = key.getLittleEndianUInt(i)
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h = h xor k.mix(R1_32, C1_32, C2_32)
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h = h.rotateLeft(R2_32)
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h = h * M_32 + N_32
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}
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val index = nblocks * 4
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val rem = len - index
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var k = 0u
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if (rem == 3) {
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k = k xor (key.getUInt(index + 2) shl 16)
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}
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if (rem >= 2) {
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k = k xor (key.getUInt(index + 1) shl 8)
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}
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if (rem >= 1) {
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k = k xor key.getUInt(index)
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h = h xor k.mix(R1_32, C1_32, C2_32)
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}
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h = h xor len.toUInt()
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h = h.fmix()
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return h
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}
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private fun ByteArray.getLittleEndianUInt(index: Int): UInt {
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return this.getUInt(index) or
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(this.getUInt(index + 1) shl 8) or
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(this.getUInt(index + 2) shl 16) or
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(this.getUInt(index + 3) shl 24)
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}
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private fun ByteArray.getLittleEndianLong(index: Int): ULong {
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return this.getULong(index) or
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(this.getULong(index + 1) shl 8) or
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(this.getULong(index + 2) shl 16) or
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(this.getULong(index + 3) shl 24) or
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(this.getULong(index + 4) shl 32) or
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(this.getULong(index + 5) shl 40) or
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(this.getULong(index + 6) shl 48) or
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(this.getULong(index + 7) shl 56)
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}
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private fun UInt.mix(r: Int, c1: UInt, c2: UInt): UInt {
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var k = this
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k *= c1
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k = k.rotateLeft(r)
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k *= c2
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return k
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}
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private fun ULong.mix(r: Int, c1: ULong, c2: ULong): ULong {
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var k = this
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k *= c1
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k = k.rotateLeft(r)
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k *= c2
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return k
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}
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private fun UInt.fmix(): UInt {
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var h = this
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h = h xor (h shr 16)
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h *= 0x85ebca6bu
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h = h xor (h shr 13)
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h *= 0xc2b2ae35u
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h = h xor (h shr 16)
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return h
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}
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private fun ULong.fmix(): ULong {
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var h = this
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h = h xor (h shr 33)
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h *= 0xff51afd7ed558ccduL
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h = h xor (h shr 33)
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h *= 0xc4ceb9fe1a85ec53uL
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h = h xor (h shr 33)
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return h
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}
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private fun ByteArray.getUInt(index: Int) = get(index).toUByte().toUInt()
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private fun ByteArray.getULong(index: Int) = get(index).toUByte().toULong()
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private companion object {
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private const val C1_32: UInt = 0xcc9e2d51u
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private const val C2_32: UInt = 0x1b873593u
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private const val R1_32: Int = 15
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private const val R2_32: Int = 13
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private const val M_32: UInt = 5u
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private const val N_32: UInt = 0xe6546b64u
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private const val C1_128x86: UInt = 0x239b961bu
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private const val C2_128x86: UInt = 0xab0e9789u
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private const val C3_128x86: UInt = 0x38b34ae5u
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private const val C4_128x86: UInt = 0xa1e38b93u
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private const val R1_128x86: Int = 15
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private const val R2_128x86: Int = 16
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private const val R3_128x86: Int = 17
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private const val R4_128x86: Int = 18
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private const val R5_128x86: Int = 19
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private const val R6_128x86: Int = 13
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private const val M_128x86: UInt = 5u
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private const val N1_128x86: UInt = 0x561ccd1bu
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private const val N2_128x86: UInt = 0x0bcaa747u
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private const val N3_128x86: UInt = 0x96cd1c35u
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private const val N4_128x86: UInt = 0x32ac3b17u
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private const val C1_128x64: ULong = 0x87c37b91114253d5uL
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private const val C2_128x64: ULong = 0x4cf5ad432745937fuL
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private const val R1_128x64: Int = 31
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private const val R2_128x64: Int = 27
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private const val R3_128x64: Int = 33
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private const val M_128x64: ULong = 5u
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private const val N1_128x64: ULong = 0x52dce729u
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private const val N2_128x64: ULong = 0x38495ab5u
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}
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}

‎src/test/kotlin/com/featurevisor/sdk/BucketTest.kt

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package com.featurevisor.sdk
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import kotlin.test.Test
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import kotlin.test.assertEquals
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class BucketTest {
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@Test
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fun getBucketedNumberReturnsExpectedValues() {
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val expectedResults =
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mapOf(
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"foo" to 20602,
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"bar" to 89144,
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"123.foo" to 3151,
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"123.bar" to 9710,
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"123.456.foo" to 14432,
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"123.456.bar" to 1982
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)
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for ((key, value) in expectedResults) {
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val result = Bucket.getBucketedNumber(key)
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assertEquals(value, result, "Expected: $value for $key, got: $result")
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}
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}
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}

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