From 1a7f32b9db37536b3f25c8abb849887c848c5795 Mon Sep 17 00:00:00 2001
From: qhga <phga@posteo.de>
Date: Sun, 23 Jan 2022 19:38:28 +0100
Subject: [PATCH] feat: Klausur SS2018

---
 .../java/edu/thi/phga/aparapi_test/App.java   |  4 ++
 .../thi/phga/aparapi_test/PraefixSumme.java   | 52 +++++++++++++++++++
 2 files changed, 56 insertions(+)
 create mode 100644 src/main/java/edu/thi/phga/aparapi_test/PraefixSumme.java

diff --git a/src/main/java/edu/thi/phga/aparapi_test/App.java b/src/main/java/edu/thi/phga/aparapi_test/App.java
index 98a36d0..45d861e 100644
--- a/src/main/java/edu/thi/phga/aparapi_test/App.java
+++ b/src/main/java/edu/thi/phga/aparapi_test/App.java
@@ -116,6 +116,10 @@ public class App {
         java.util.Arrays.fill(b, 1);
         OpenCLPrefix2.start(b);
         break;
+      case 33:
+        // Klausur SS2018
+        PraefixSumme.start();
+        break;
       case 40:
         // multiParam defines smoothing
         System.out.println("Spawning window Filter");
diff --git a/src/main/java/edu/thi/phga/aparapi_test/PraefixSumme.java b/src/main/java/edu/thi/phga/aparapi_test/PraefixSumme.java
new file mode 100644
index 0000000..663adbc
--- /dev/null
+++ b/src/main/java/edu/thi/phga/aparapi_test/PraefixSumme.java
@@ -0,0 +1,52 @@
+package edu.thi.phga.aparapi_test;
+
+import java.util.Arrays;
+
+import com.aparapi.Kernel;
+
+public class PraefixSumme {
+  public static void start() {
+    int[] a = {4, 3, 6, 2, 1, 5, 9, 7};
+    praefixsummme(a);
+    System.out.println(Arrays.toString(a));
+  }
+
+  public static void praefixsummme(int[] a) {
+    int N = a.length;
+    int[] b = Arrays.copyOf(a, N * 2);
+
+    class PraefixKernel extends Kernel {
+      private int offset = 0;
+      private int stepSize;
+
+      public void setOffset() {
+        offset = N - offset;
+      }
+
+      public int getOffset() {
+        return offset;
+      }
+
+      public void setStepSize(int s) {
+        stepSize = s;
+      }
+
+      @Override public void run() {
+        int i = getGlobalId(0);
+        if (i >= stepSize) {
+          b[offset + i] = b[N - offset + i] + b[N - offset + i - stepSize];
+        }
+      }
+    }
+
+    PraefixKernel k = new PraefixKernel();
+
+    for (int j = 1; j < N; j *= 2) {
+      k.setOffset();
+      k.setStepSize(j);
+      k.execute(N);
+    }
+
+    Arrays.parallelSetAll(a, i -> b[k.getOffset() + i]);
+  }
+}