Optimise memory usage while computing Murmur2

src/main/java/link/infra/packwiz/installer/metadata/hash/Murmur2Lib.java

@@ -74,13 +74,13 @@ public class Murmur2Lib {
     int left = length - len_m;
     if (left != 0) {
       if (left >= 3) {
-        h ^= (int) data[length - 3] << 16;
+        h ^= (int) data[length - (left - 2)] << 16;
       }
       if (left >= 2) {
-        h ^= (int) data[length - 2] << 8;
+        h ^= (int) data[length - (left - 1)] << 8;
       }
       if (left >= 1) {
-        h ^= (int) data[length - 1];
+        h ^= data[length - left];
       }
 
       h *= M_32;
@@ -152,7 +152,7 @@ public class Murmur2Lib {
       case 2:
         h ^= (long) (data[tailStart + 1] & 0xff) << 8;
       case 1:
-        h ^= (long) (data[tailStart] & 0xff);
+        h ^= data[tailStart] & 0xff;
         h *= M_64;
     }
 

src/main/kotlin/link/infra/packwiz/installer/metadata/hash/Murmur2Hasher.kt

@@ -10,7 +10,7 @@ class Murmur2Hasher : IHasher {
 		val tempBuffer = Buffer()
 
 		override val hash: Hash by lazy(LazyThreadSafetyMode.NONE) {
-			val data = computeNormalizedArray(internalBuffer.readByteArray())
+			val data = internalBuffer.readByteArray()
 			Murmur2Hash(Murmur2Lib.hash32(data, data.size, 1))
 		}
 
@@ -19,27 +19,42 @@ class Murmur2Hasher : IHasher {
 			val out = delegate.read(tempBuffer, byteCount)
 			if (out > -1) {
 				sink.write(tempBuffer.clone(), out)
-				internalBuffer.write(tempBuffer, out)
+				computeNormalizedBufferFaster(tempBuffer, internalBuffer)
 			}
 			return out
 		}
 
 		// Credit to https://github.com/modmuss50/CAV2/blob/master/murmur.go
-		private fun computeNormalizedArray(input: ByteArray): ByteArray {
+//		private fun computeNormalizedArray(input: ByteArray): ByteArray {
-			val output = ByteArray(input.size)
+//			val output = ByteArray(input.size)
+//			var index = 0
+//			for (b in input) {
+//				when (b) {
+//					9.toByte(), 10.toByte(), 13.toByte(), 32.toByte() -> {}
+//					else -> {
+//						output[index] = b
+//						index++
+//					}
+//				}
+//			}
+//			val outputTrimmed = ByteArray(index)
+//			System.arraycopy(output, 0, outputTrimmed, 0, index)
+//			return outputTrimmed
+//		}
+
+		private fun computeNormalizedBufferFaster(input: Buffer, output: Buffer) {
 			var index = 0
-			for (b in input) {
+			val arr = input.readByteArray()
-				when (b.toInt()) {
+			for (b in arr) {
-					9, 10, 13, 32 -> {}
+				when (b) {
+					9.toByte(), 10.toByte(), 13.toByte(), 32.toByte() -> {}
 					else -> {
-						output[index] = b
+						arr[index] = b
 						index++
 					}
 				}
 			}
-			val outputTrimmed = ByteArray(index)
+			output.write(arr, 0, index)
-			System.arraycopy(output, 0, outputTrimmed, 0, index)
-			return outputTrimmed
 		}
 
 	}