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    <p>I can give you some hint as I was also facing similar problem. </p> <p>I can think of three different methods for achieving similar goal:</p> <p>Consider a simple kernel, assuming you launched 4 (0-3) threads </p> <pre><code>_kernel void addition (int *p) { int i = get_local_id(0); p[4]+= p[i]; } </code></pre> <p>You want to add values p[0], p[1], p[2], p[3], p[4], and store the final sum in p[4]. right? i.e:</p> <pre><code>p[4]= p[0] + p[1] + p[2] + p[3] + p[4] </code></pre> <p><strong>Method -1</strong> (no parallelism)</p> <p>Assign this job to only 1 thread (no parallelism):</p> <pre><code>int i = get_local_id(0); if (i==0) { p[4]+= p[i]; } </code></pre> <p><strong>Method-2</strong> (with parallelism)</p> <p>Express your problem as follows: </p> <pre><code>p[4]= p[0] + p[1] + p[2] + p[3] + p[4] + 0 </code></pre> <p>This is a reduction problem </p> <p>So launch 3 threads: i=0 to i=2. In first iteration </p> <pre><code> i=0 finds p[0] + p[1] i=1 finds p[2] + p[3] i=2 finds p[4] + 0 </code></pre> <p>Now you have three numbers, you apply the same logic as above and add these numbers (with suitable padding of 0 to make it in power of two) </p> <p><strong>Method -3</strong> Atomic operations</p> <p>If you still need to implement this atomically, you can use <a href="http://www.khronos.org/registry/cl/sdk/1.2/docs/man/xhtml/atomic_add.html" rel="nofollow">atomic_add()</a>:</p> <pre><code> int fsfunc atomic_add ( volatile __global int *p ,int val) </code></pre> <blockquote> <p>Description</p> <p>Read the 32-bit value (referred to as old) stored at location pointed by p. Compute (old + val) and store result at location pointed by p. The function returns old.</p> </blockquote> <p>This is assuming the data is int type. Otherwise you can see the <a href="http://suhorukov.blogspot.co.uk/2011/12/opencl-11-atomic-operations-on-floating.html" rel="nofollow">link</a> as suggested above. </p>
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    1. USMichał Walenciak
    1. USgpuguy
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    1. COIt means if I am using floating point operations,then I don't any other option than using the reduction method, as there isn't any provision of extensions for floating point based atomic operations (as far as my information in concerned). Am I right?
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      1. USsandeep.ganage
    2. COApart from reduction you can also see the [link](http://suhorukov.blogspot.co.uk/2011/12/opencl-11-atomic-operations-on-floating.html) posted by @Slicedpan
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