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POCan this code be optimised?
 

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  1. POCan this code be optimised?
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    <p>I have some image processing code that loops through 2 multi-dimensional byte arrays (of the same size). It takes a value from the source array, performs a calculation on it and then stores the result in another array.</p> <pre><code>int xSize = ResultImageData.GetLength(0); int ySize = ResultImageData.GetLength(1); for (int x = 0; x &lt; xSize; x++) { for (int y = 0; y &lt; ySize; y++) { ResultImageData[x, y] = (byte)((CurrentImageData[x, y] * AlphaValue) + (AlphaImageData[x, y] * OneMinusAlphaValue)); } } </code></pre> <p>The loop currently takes ~11ms, which I assume is mostly due to accessing the byte arrays values as the calculation is pretty simple (2 multiplications and 1 addition).</p> <p>Is there anything I can do to speed this up? It is a time critical part of my program and this code gets called 80-100 times per second, so any speed gains, however small will make a difference. Also at the moment xSize = 768 and ySize = 576, but this will increase in the future.</p> <p><strong>Update</strong>: Thanks to <a href="https://stackoverflow.com/users/69083/guffa">Guffa</a> (see answer below), the following code saves me 4-5ms per loop. Although it is <em>unsafe</em> code.</p> <pre><code>int size = ResultImageData.Length; int counter = 0; unsafe { fixed (byte* r = ResultImageData, c = CurrentImageData, a = AlphaImageData) { while (size &gt; 0) { *(r + counter) = (byte)(*(c + counter) * AlphaValue + *(a + counter) * OneMinusAlphaValue); counter++; size--; } } } </code></pre>
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    1. USMatt Warren
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    1. CO@Andrew Arnott: Although completely correct, also completely useless. ;)
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    2. COCan you update with the timing for the code in the accepted answer? It would be interesting to know how much difference it makes saving the 3 additions of counter per loop iteration.
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      1. USPeter Mortensen
    3. COIf you look at the "UPDATE" section of my question it's there. The code based on the accepted answer takes 6-7 ms per loop, compared to ~11 ms for the original code. Does this help or are you asking about some other version of the code?
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      1. USMatt Warren
 

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