--- a/src/parallel_execution/examples/twice/CUDAtwice.cu	Thu Sep 14 02:35:20 2017 +0900
+++ b/src/parallel_execution/examples/twice/CUDAtwice.cu	Thu Sep 14 18:26:52 2017 +0900
@@ -1,8 +1,14 @@
 extern "C" {
 
 #include <stdio.h>
-    __global__ void twice(int* array) {
-        printf("array %p",array);
-        array[blockIdx.x] = array[blockIdx.x]*2;
+    __global__ void twice(int* array, int* prefixPtr) {
+        int i = 0;
+        int prefix = *prefixPtr;
+C_twice:
+        if (i < prefix) {
+            array[i+blockIdx.x*prefix] = array[i+blockIdx.x*prefix]*2;
+            i++;
+            goto C_twice;
+        }
     }
 }