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    <p>I think you may be measuring the cache/memory performance, more than the branch prediction. Your inner 'work' loop is accessing an ever increasing chunk of memory. Which may explain the linear growth, the periodic behaviour, etc.</p> <p>I could be wrong, as I've not tried replicating your results, but if I were you I'd factor out memory accesses before timing other things. Perhaps sum one volatile variable into another, rather than working in an array.</p> <p>Note also that, depending on the CPU, the branch prediction can be a lot smarter than just recording the last time a branch was taken - repeating patterns, for example, aren't as bad as random data.</p> <p>Ok, a quick and dirty test I knocked up on my tea break which tried to mirror your own test method, but without thrashing the cache, looks like this:</p> <p><img src="https://i.stack.imgur.com/xWeIR.png" alt="enter image description here"></p> <p>Is that more what you expected?</p> <p>If I can spare any time later there's something else I want to try, as I've not really looked at what the compiler is doing...</p> <p><strong>Edit:</strong></p> <p>And, here's my final test - I recoded it in assembler to remove the loop branching, ensure an exact number of instructions in each path, etc. </p> <p><img src="https://i.stack.imgur.com/z87lL.png" alt="More branch prediction results"></p> <p>I also added an extra case, of a 5-bit repeating pattern. It seems pretty hard to upset the branch predictor on my ageing Xeon.</p>
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    1. POBranch Prediction: Writing Code to Understand it; Getting Weird Results
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    1. CO+1 BTW what tool are you both using for plotting results?
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    2. CO@doc MS Office Excel 2007
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    3. CO+1 for actually trying it yourself - I take the "111" in the legend is just as good as "1" (i.e. always "1")? If so, that doesn't seem *that* interesting given that you already checked the "always zero" case (and indeed, the two graphs are basically the same).
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      1. USFrerich Raabe
 

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