Unsafe Context
/*
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;
}
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