From ce71b26015c3225790f05ab55a81fa5749d1d92c Mon Sep 17 00:00:00 2001
From: HoaPhan <s50600822@gmail.com>
Date: Thu, 28 Mar 2024 17:06:55 +1100
Subject: [PATCH] speculative_execution

---
 vs/java/speculative_execution/README.md | 95 +++++++++++++++++++++++++
 1 file changed, 95 insertions(+)
 create mode 100644 vs/java/speculative_execution/README.md

diff --git a/vs/java/speculative_execution/README.md b/vs/java/speculative_execution/README.md
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@@ -0,0 +1,95 @@
+### Ref
+https://en.wikipedia.org/wiki/Speculative_execution
+
+
+### example
+
+#### code
+```java
+public class SortedVsUnsortedArray {
+    static final int LENGTH = 1000000;
+
+    public static void main(String[] args) {
+
+        int[] sortedArray = new int[LENGTH];
+            for (int i = 0; i < LENGTH; i++) {
+            sortedArray[i] = i;
+        }
+        
+        int[] unsortedArray = new int[LENGTH];
+        for (int i = 0; i < LENGTH; i++) {
+            unsortedArray[i] = i;
+        }
+        shuffleArray(unsortedArray);
+        
+        long startTime = System.nanoTime();
+        touch(sortedArray);
+        long endTime = System.nanoTime();
+        long durationSorted = endTime - startTime;
+
+        startTime = System.nanoTime();
+        touch(unsortedArray);
+        endTime = System.nanoTime();
+        long durationUnsorted = endTime - startTime;
+
+        System.out.println("Time taken for sorted array: " + durationSorted + " nanoseconds");
+        System.out.println("Time taken for unsorted array: " + durationUnsorted + " nanoseconds");
+    }
+
+    /**
+     * Fisher-Yates shuffle algorithm
+     */ 
+    private static void shuffleArray(int[] array) {
+        int index, temp;
+        for (int i = array.length - 1; i > 0; i--) {
+            index = (int) (Math.random() * (i + 1));
+            temp = array[index];
+            array[index] = array[i];
+            array[i] = temp;
+        }
+    }
+
+    private static void touch(int[] arr) {
+        for (int p = 0; p < arr.length; p++) {
+            arr[p]++;
+        }
+    }   
+}
+```
+
+
+
+#### observation
+dew it `java SortedVsUnsortedArray.java && java SortedVsUnsortedArray`
+```bash
+for i in {1..7}; do java SortedVsUnsortedArray.java && java SortedVsUnsortedArray; done
+
+Time taken for sorted array: 2234625 nanoseconds
+Time taken for unsorted array: 3232291 nanoseconds
+Time taken for sorted array: 2318583 nanoseconds
+Time taken for unsorted array: 3390084 nanoseconds
+Time taken for sorted array: 2592000 nanoseconds
+Time taken for unsorted array: 1975041 nanoseconds
+Time taken for sorted array: 2487416 nanoseconds
+Time taken for unsorted array: 3636333 nanoseconds
+Time taken for sorted array: 2494458 nanoseconds
+Time taken for unsorted array: 1964666 nanoseconds
+Time taken for sorted array: 2296417 nanoseconds
+Time taken for unsorted array: 2056542 nanoseconds
+Time taken for sorted array: 2391250 nanoseconds
+Time taken for unsorted array: 3750333 nanoseconds
+Time taken for sorted array: 2301084 nanoseconds
+Time taken for unsorted array: 3297375 nanoseconds
+Time taken for sorted array: 2475250 nanoseconds
+Time taken for unsorted array: 3322667 nanoseconds
+Time taken for sorted array: 2303584 nanoseconds
+Time taken for unsorted array: 3338125 nanoseconds
+Time taken for sorted array: 2431792 nanoseconds
+Time taken for unsorted array: 3301833 nanoseconds
+Time taken for sorted array: 2231875 nanoseconds
+Time taken for unsorted array: 3311333 nanoseconds
+Time taken for sorted array: 2451375 nanoseconds
+Time taken for unsorted array: 1949875 nanoseconds
+Time taken for sorted array: 2254917 nanoseconds
+Time taken for unsorted array: 3331500 nanoseconds
+```
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