Faster memory compare

Author: emyfops

src/main/kotlin/com/lambda/graphics/buffer/DynamicByteBuffer.kt

@@ -150,8 +150,8 @@ class DynamicByteBuffer private constructor(initialCapacity: Int) {
         val offset = position - pointer
 
         memCopy(pointer, newPointer, offset)
-        data = newBuffer
 
+        data = newBuffer
         pointer = newPointer
         position = newPointer + offset
         capacity = newCapacity
@@ -176,6 +176,13 @@ class DynamicByteBuffer private constructor(initialCapacity: Int) {
         capacity = newCapacity
     }
 
+    /**
+     * Returns the relative index of the first mismatch between this and the given buffer, otherwise -1 if no mismatch.
+     *
+     * @see [ByteBuffer.mismatch]
+     */
+    fun mismatch(other: DynamicByteBuffer) = data.mismatch(other.data)
+
     companion object {
         /**
          * Creates a new DynamicByteBuffer with specified initial capacity
@@ -184,4 +191,4 @@ class DynamicByteBuffer private constructor(initialCapacity: Int) {
         fun dynamicByteBuffer(initialCapacity: Int) =
             DynamicByteBuffer(initialCapacity)
     }
-}
+}

src/main/kotlin/com/lambda/graphics/pipeline/PersistentBuffer.kt

@@ -18,10 +18,8 @@
 package com.lambda.graphics.pipeline
 
 import com.lambda.graphics.buffer.Buffer.Companion.createPipelineBuffer
-import com.lambda.graphics.buffer.DynamicByteBuffer
 import com.lambda.graphics.buffer.DynamicByteBuffer.Companion.dynamicByteBuffer
 import com.lambda.graphics.gl.kibibyte
-import org.lwjgl.system.MemoryUtil
 import org.lwjgl.system.MemoryUtil.memCopy
 
 /**
@@ -64,7 +62,7 @@ class PersistentBuffer(
         }
 
         if (snapshotData > 0 && snapshot.capacity >= byteBuffer.bytesPut) {
-            if (memcmp(snapshot, byteBuffer, uploadOffset, dataCount)) return
+            if (snapshot.mismatch(byteBuffer) >= 0) return
         }
 
         glBuffer.update(uploadOffset, dataCount, dataStart)
@@ -90,30 +88,4 @@ class PersistentBuffer(
     }
 
     fun use(block: () -> Unit) = glBuffer.bind { block() }
-
-    private fun memcmp(a: DynamicByteBuffer, b: DynamicByteBuffer, position: Long, size: Long): Boolean {
-        if (a.capacity != b.capacity) return false
-
-        val end = position + size
-        var head = position
-
-        // Process the aligned bytes in chunks of 8 until we've reached the end
-        while (head + 8 <= end) {
-            val first = MemoryUtil.memGetLong(a.pointer + head)
-            val second = MemoryUtil.memGetLong(b.pointer + head)
-            if (first != second) return false
-
-            head += 8
-        }
-
-        while (head < end) {
-            val first = MemoryUtil.memGetByte(a.pointer + head)
-            val second = MemoryUtil.memGetByte(b.pointer + head)
-            if (first != second) return false
-
-            head++
-        }
-
-        return true
-    }
 }