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POwhy unsafe block with pointers is slower than regular version
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  1. POwhy unsafe block with pointers is slower than regular version
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    copied!<p>I am testing using unsafe and pointers on character match counting a 200 byte array along every position in a 1 meg long char array as an experiment with safe/unsafe/dll call speed comparison.</p> <p>They are run in release mode with optimize code on, allow unsafe, no bounds checking. Long char array is used purposely used to minimize calling overhead impacts.</p> <p>The times i get are</p> <blockquote> <p>regular 560 ms</p> <p>unsafe 830 ms</p> <p>dll 205 ms</p> </blockquote> <p>why is the unsafe slower??</p> <pre><code> byte[] buffer = new Byte[1000000]; byte[] check = new Byte[1000]; [DllImport("sortitdev.dll", CallingConvention=CallingConvention.StdCall)] //[DllImport("sortitfast.dll", CallingConvention=CallingConvention.StdCall)] //[DllImport("sortitpellas.dll", CallingConvention=CallingConvention.StdCall)] public unsafe static extern void sortitt([MarshalAs(UnmanagedType.LPArray)] byte[] buffer); public MainForm() { InitializeComponent(); } void Button1Click(object sender, EventArgs e) // do char array matching { byte match; Random rnd = new Random(); for(int i=0;i&lt;1000000;i++) buffer[i]=(byte)rnd.Next(0,256); for(int i=0;i&lt;200;i++) check[i]=(byte)rnd.Next(0,256); Stopwatch sw = Stopwatch.StartNew(); int kk=0; int jq=0; while(kk&lt;999000) { kk++; match=0; for(jq=0;jq&lt;199;jq++) if(buffer[kk+jq]==check[jq])match++; buffer[kk]=match; } sw.Stop(); textBox1.Text= sw.Elapsed.TotalMilliseconds.ToString(); sw.Reset(); sw.Start(); unsafe { fixed (byte* bufptr=&amp;buffer[0] , chckptr=&amp;check[0]) { byte* bufptrC=bufptr; // modifiable pointer byte* chckptrC=chckptr; byte* bufhldptr; byte* chckhldptr; int k=999000; int jw=0; while(k&gt;0) { bufhldptr=bufptrC; match=0; chckhldptr=chckptrC; for(jw=0;jw&lt;199;jw++) if(*bufhldptr++==*chckhldptr++)match++; *bufptrC++=match; k--; } } sw.Stop(); textBox2.Text= sw.Elapsed.TotalMilliseconds.ToString(); } sw.Reset(); for(int tt=0;tt&lt;200;tt++) buffer[tt]=(byte)tt; sw.Start(); unsafe { fixed(byte* dadata=&amp;buffer[0]) { sortitt(buffer); } } sw.Stop(); textBox3.Text= sw.Elapsed.TotalMilliseconds.ToString(); int kll=(int)buffer[1]; textBox4.Text= kll.ToString(); } } </code></pre>
 

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