Insertion sort was *super* busted I don't even know how it worked

code/libraries/array/src/main/java/nu/marginalia/array/algo/IntArraySort.java

@@ -48,27 +48,10 @@ public interface IntArraySort extends IntArrayBase {
         return true;
     }
 
-
-
     default void insertionSort(long start, long end) {
         assert end - start < Integer.MAX_VALUE;
 
-        int n = (int) (end - start);
+        SortAlgoInsertionSort._insertionSort(this, start, end);
-
-        if (n <= 1) {
-            return;
-        }
-
-        for (int i = 1; i < n; i++) {
-            int key = get(start + i);
-
-            int j = i - 1;
-            while (j >= 0 && get(start + j) > key) {
-                swap( start + j, start + (long)(j+1));
-                j--;
-            }
-            set(start + j+1, key);
-        }
     }
 
     default void quickSort(long start, long end) {

code/libraries/array/src/main/java/nu/marginalia/array/algo/LongArrayBase.java

@@ -70,6 +70,9 @@ public interface LongArrayBase extends BulkTransferArray<LongBuffer> {
             buffer[(int) i] = get(start + i);
         }
     }
+    default void get(long start, long[] buffer) {
+        get(start, start + buffer.length, buffer);
+    }
 
     void write(Path file) throws IOException;
 

code/libraries/array/src/main/java/nu/marginalia/array/algo/SortAlgoInsertionSort.java

@@ -14,15 +14,18 @@ class SortAlgoInsertionSort {
             return;
         }
 
-        for (int i = 1; i < span / sz; i++) {
+        long[] buf = new long[sz];
-            long key = array.get(start + (long) i * sz);
+        for (long i = 1; i < span / sz; i++) {
+            array.get(start + i * sz, buf);
+
+            long key = buf[0];
 
             long j;
-            for (j = i - 1; j >= 0 && array.get(start + j* sz) > key; j--) {
+            for (j = i - 1; j >= 0 && array.get(start + j * sz) > key; j--) {
-                array.swapn(sz, start + j *sz, start + (j + 1)*sz);
+                shiftN(array, sz, start + j * sz, start + (j + 1) * sz, sz);
             }
 
-            array.set(start + (j + 1) * sz, key);
+            array.set(start + (j + 1) * sz, buf);
         }
     }
 
@@ -40,9 +43,50 @@ class SortAlgoInsertionSort {
 
             int j;
             for (j = i - 1; j >= 0 && array.get(start + j) > key; j--) {
-                array.swap(start + j, start + j + 1);
+                shift(array, start + j, start + j + 1, 1);
             }
+
             array.set(start + j + 1, key);
         }
     }
+    static void _insertionSort(IntArraySort array, long start, long end) {
+        assert end - start < Integer.MAX_VALUE;
+
+        int n = (int) (end - start);
+
+        if (n <= 1) {
+            return;
+        }
+
+        for (int i = 1; i < n; i++) {
+            int key = array.get(start + i);
+
+            int j;
+            for (j = i - 1; j >= 0 && array.get(start + j) > key; j--) {
+                shift(array, start + j, start + j + 1, 1);
+            }
+
+            array.set(start + j + 1, key);
+        }
+    }
+
+    private static void shiftN(LongArraySort array, int sz, long start, long end, long shift) {
+        for (long i = start; i < end; i+=sz) {
+            for (int j = 0; j < sz; j++) {
+                array.set(i + j + shift, array.get(i + j));
+            }
+        }
+    }
+    private static void shift(LongArraySort array, long start, long end, long shift) {
+        for (long i = start; i < end; i++) {
+            array.set(i + shift, array.get(i));
+        }
+    }
+
+    private static void shift(IntArraySort array, long start, long end, long shift) {
+        for (long i = start; i < end; i++) {
+            array.set(i + shift, array.get(i));
+        }
+    }
+
 }