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    <p>(Disclaimer: the following deals with very low-level optimizations that are most often not necessary. If you keep reading, you waive your right to complain that computers are fast and there is never any reason to worry about this sort of thing.)</p> <p>One advantage of eliminating an <code>if</code> statement is that you avoid branch prediction penalties. </p> <p>Branch prediction penalties are generally only a problem when the branch is not easily predicted. A branch is easily predicted when it is almost always taken/not taken, or it follows a simple pattern. For example, the branch in a loop statement is taken every time except the last one, so it is easily predicted. However, if you have code like</p> <pre><code>a = random() % 10 if (a &lt; 5) print "Less" else print "Greater" </code></pre> <p>then this branch is not easily predicted, and will frequently incur the prediction penalty associated with clearing the cache and rolling back instructions that were executed in the wrong part of the branch.</p> <p>One way to avoid these kinds of penalties is to use the ternary (<code>?:</code>) operator. In simple cases, the compiler will generate conditional move instructions rather than branches.</p> <p>So</p> <pre><code>int a, b, low; if (a &lt; b) low = a; else low = b; </code></pre> <p>becomes</p> <pre><code>int a, b, low; low = (a &lt; b) ? a : b </code></pre> <p>and in the second case a branching instruction is not necessary. Additionally, it is much clearer and more readable than your bit-twiddling implementation.</p> <p>Of course, this is a micro-optimization which is unlikely to have significant impact on your code.</p>
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    1. POHow efficient is an if statement compared to a test that doesn't use an if? (C++)
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    1. USdanben
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    1. COFinally, an answer that isn't bleating about premature optimization. Thank you.
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      1. USJusticle
    2. CO@Justicle - the problem with not bleating about premature optimization is that you end up with an implied suggestion (particularly to people who are just learning) that one should write code like `low = b + ((a - b) & ((a - b) >> 31))` everywhere for no good reason because someone said "it's faster". When, in fact, it's the wrong thing to do the vast majority of times.
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      1. USMichael Burr
    3. COAt `-O1` and higher, gcc produces identical code for the if statement and the ternary operator for the min() function, using a cmovg instruction in both cases. At `-O0`, it uses branches and labels for the if statement and cmovle for the ternary operator.
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      1. USAdam Rosenfield
 

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