Unsafe Context

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/*
A Programmer's Introduction to C# (Second Edition)
by Eric Gunnerson

Publisher: Apress L.P.
ISBN: 1-893115-62-3
*/
// 36 – Deeper into C#Unsafe Context
// copyright 2000 Eric Gunnerson
// file=unsafe.cs
// compile with: csc /unsafe /o+ unsafe.cs
using System;
using System.Diagnostics;
using System.Runtime.InteropServices;

public class UnsafeContext
{
const int iterations = 20000; // # to do copy
const int points = 1000; // # of points in array
const int retryCount = 5; // # of times to retry

public delegate Point[] CloneFunction(Point[] a);

public static void TimeFunction(Point[] arr,
CloneFunction func, string label)
{
Point[] arrCopy = null;
long start;
long delta;
double min = 5000.0d; // big number;

// do the whole copy retryCount times, find fastest time
for (int retry = 0; retry < retryCount; retry++) { start = Counter.Value; for (int iterate = 0; iterate < iterations; iterate++) arrCopy = func(arr); delta = Counter.Value - start; double result = (double) delta / Counter.Frequency; if (result < min) min = result; } Console.WriteLine("{0}: {1:F3} seconds", label, min); } public static void Main() { Console.WriteLine("Points, Iterations: {0} {1}", points, iterations); Point[] arr = new Point[points]; for (int index = 0; index < points; index++) arr[index] = new Point(3, 5); TimeFunction(arr, new CloneFunction(Point.ClonePointArrayMemcpy), "Memcpy"); TimeFunction(arr, new CloneFunction(Point.ClonePointArrayUnsafe), "Unsafe"); TimeFunction(arr, new CloneFunction(Point.ClonePointArray), "Baseline"); } } class Counter { public static long Frequency { get { long freq = 0; QueryPerformanceFrequency(ref freq); return freq; } } public static long Value { get { long count = 0; QueryPerformanceCounter(ref count); return count; } } [System.Runtime.InteropServices.DllImport("KERNEL32", CharSet=System.Runtime.InteropServices.CharSet.Auto)] private static extern bool QueryPerformanceCounter( ref long lpPerformanceCount); [System.Runtime.InteropServices.DllImport("KERNEL32", CharSet=System.Runtime.InteropServices.CharSet.Auto)] private static extern bool QueryPerformanceFrequency( ref long lpFrequency); } public struct Point { public Point(int x, int y) { this.x = x; this.y = y; } // safe version public static Point[] ClonePointArray(Point[] a) { Point[] ret = new Point[a.Length]; for (int index = 0; index < a.Length; index++) ret[index] = a[index]; return(ret); } // unsafe version using pointer arithmetic unsafe public static Point[] ClonePointArrayUnsafe(Point[] a) { Point[] ret = new Point[a.Length]; // a and ret are pinned; they cannot be moved by // the garbage collector inside the fixed block. fixed (Point* src = a, dest = ret) { Point* pSrc = src; Point* pDest = dest; for (int index = 0; index < a.Length; index++) { *pDest = *pSrc; pSrc++; pDest++; } } return(ret); } // import CopyMemory from kernel32 [DllImport("kernel32.dll")] unsafe public static extern void CopyMemory(void* dest, void* src, int length); // unsafe version calling CopyMemory() unsafe public static Point[] ClonePointArrayMemcpy(Point[] a) { Point[] ret = new Point[a.Length]; fixed (Point* src = a, dest = ret) { CopyMemory(dest, src, a.Length * sizeof(Point)); } return(ret); } public override string ToString() { return(String.Format("({0}, {1})", x, y)); } int x; int y; } [/csharp]