shift func on UnsafeLong2D

src/net/torvald/unsafe/UnsafeLong2D.kt

@@ -1,5 +1,7 @@
 package net.torvald.unsafe
 
+import kotlin.math.absoluteValue
+
 /**
  * Created by minjaesong on 2024-07-22.
  */
@@ -8,7 +10,9 @@ class UnsafeLong2D(width: Int, height: Int) {
     val width = width.toLong()
     val height = height.toLong()
 
-    private val ptr = UnsafeHelper.allocate(8L * width * height)
+    private val WORDSIZE = 8L
+
+    private val ptr = UnsafeHelper.allocate(WORDSIZE * width * height)
 
     private inline fun toIndex(y: Int, x: Int) = width * y + x
 
@@ -19,4 +23,44 @@ class UnsafeLong2D(width: Int, height: Int) {
     val destroyed: Boolean
         get() = ptr.destroyed
 
+    /**
+     * The contents of the "outer" region are undefined.
+     *
+     * If any of the displacement is equal to or larger than the dimension, nothing will be done.
+     *
+     * @param xoff positive values to shift to right, negative values to shift to left
+     * @param yoff positive values to shift to down, negative values to shift to up
+     *
+     * @return `true` if the displacement is smaller than the size, `false` otherwise
+     */
+    fun shift(xoff: Int, yoff: Int): Boolean {
+        val xoff = xoff.toLong()
+        val yoff = yoff.toLong()
+
+        val xsize = width - xoff.absoluteValue
+        val ysize = height - yoff.absoluteValue
+
+        if (xsize >= width || ysize >= height) return false
+
+        val ys = if (yoff < 0) 0 until height - ysize else height-1 downTo yoff
+        val linesize = WORDSIZE * width
+        val unsafe = UnsafeHelper.unsafe
+        val linebuf = UnsafeHelper.allocate(WORDSIZE * xsize)
+        for (y in ys) {
+            // copy
+            unsafe.copyMemory(
+                ptr.ptr + (y - yoff) * linesize - xoff.coerceAtMost(0L) * WORDSIZE,
+                linebuf.ptr,
+                WORDSIZE * xsize
+            )
+            // paste
+            unsafe.copyMemory(
+                linebuf.ptr,
+                ptr.ptr + (y) * linesize + xoff.coerceAtLeast(0L) * WORDSIZE,
+                WORDSIZE * xsize
+            )
+        }
+        return true
+    }
+
 }