code input wip

src/net/torvald/terrarum/utils/BloomFilter.kt

@@ -0,0 +1,87 @@
+package net.torvald.terrarum.utils
+
+import java.math.BigInteger
+import java.nio.ByteBuffer
+import java.security.MessageDigest
+import java.security.NoSuchAlgorithmException
+
+/**
+ * Created by minjaesong on 2023-02-05.
+ */
+class BloomFilter(capacity: Int, k: Int) {
+    private var set: ByteArray
+
+    private var keySize = 0
+    private var setSize: Int = 0
+
+    private var empty = true
+
+    private var md: MessageDigest? = null
+
+    init {
+        setSize = capacity
+        set = ByteArray(setSize)
+        keySize = k
+        empty = true
+        md = try {
+            MessageDigest.getInstance("MD5")
+        }
+        catch (e: NoSuchAlgorithmException) {
+            throw IllegalArgumentException("Error : MD5 Hash not found")
+        }
+    }
+
+    fun makeEmpty() {
+        set = ByteArray(setSize)
+        empty = true
+        md = try {
+            MessageDigest.getInstance("MD5")
+        }
+        catch (e: NoSuchAlgorithmException) {
+            throw IllegalArgumentException("Error : MD5 Hash not found")
+        }
+    }
+
+    fun restoreFromByteArray(oldSet: ByteArray) {
+        if (this.set.size != oldSet.size)
+            throw IllegalStateException("Cannot restore from bytes: expected ${this.set.size} byte-set, got ${oldSet.size} instead")
+
+        this.set = oldSet
+
+        empty = set.all { it == 0.toByte() }
+    }
+
+    fun isEmpty() = empty
+
+    private fun getHash(i: Int): Int {
+        md!!.reset()
+        val bytes: ByteArray = ByteBuffer.allocate(4).putInt(i).array()
+        md!!.update(bytes, 0, bytes.size)
+        return Math.abs(BigInteger(1, md!!.digest()).toInt()) % (set.size - 1)
+    }
+
+    fun add(obj: Int) {
+        val tmpset = getSetArray(obj)
+        for (i in tmpset) set[i] = 1
+        empty = false
+    }
+
+    operator fun contains(obj: Int): Boolean {
+        val tmpset = getSetArray(obj)
+        for (i in tmpset) if (set[i].toInt() != 1) return false
+        return true
+    }
+
+    private fun getSetArray(obj: Int): IntArray {
+        val tmpset = IntArray(keySize)
+        tmpset[0] = getHash(obj)
+        for (i in 1 until keySize) tmpset[i] = getHash(tmpset[i - 1])
+        return tmpset
+    }
+
+    fun serialise(): ByteArray {
+        val returningSet = ByteArray(setSize)
+        System.arraycopy(set, 0, returningSet, 0, setSize)
+        return returningSet
+    }
+}