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copied!<p>Regarding speed, this would be at least as fast as choice 2:</p> <pre><code>bSize = 128 << (choice == 'y' || choice == 'Y'); </code></pre> <p>Whether <em>that</em> would be faster than choice 1 is not immediately obvious to me. However, for tuned performance on an unknown platform, I think that I like the suggested variant on choice 2. The reason is that, at the hardware level, choice 2 (original or variant) does not involve reloading the program counter, but invokes a relatively straightforward <em>shift-register</em> operation, involving relatively few transistors. (Actually, if you want to get really technical about it, I am given to understand that the shift is probably accomplished by <em>multiplexing.</em> To detail that would be too much for the present format, but the point is that the output of <code>(choice == 'y' || choice == 'Y')</code> is effectively piped straight to one of the multiplexer's control lines. Anyway, it's really fast.)</p> <p>Regarding whether one can safely use the evaluated condition in the manner suggested, ISO/IEC 9899:1999 (E), sect. 6.5.14.3, guarantees that one can safely do this. It reads, "The || operator shall yield 1 if either of its operands compare unequal to 0; otherwise, it yields 0. The result has type int."</p> <p>(@PaulR rightly observes that electronic-theoretical considerations like the ones this answer offers are not decisive. One must profile actual code on an actual platform to tell for sure which is faster. Nor is this a mere quibble on @PaulR's part. It is all well to argue that choice 2 <em>would</em> be faster, but this does not mean that is <em>is</em> faster. Depending on the CPU in use, branch-predicting or other hardware could promote choice 1, nor would I be extremely surprised if it did.)</p>

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