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Computer Science

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    $\begingroup$ Generally if these are constants, a halfway decent compiler will optimize them out, generating non-wasteful code. Most CPUs do not alter execution time depending on operands within a given width/type category, but all sorts of hardware runtime optimizations have been proposed on paper, and a smaller set implemented in silicon. $\endgroup$ Commented Feb 24, 2017 at 22:29
  • $\begingroup$ For floating point numbers, multiplying by zero is a special case (as it cannot be "renormalised") $\endgroup$ Commented Feb 24, 2017 at 22:33
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    $\begingroup$ This is too broad, as you could definitively find one that does, and others that don't. What about CPUs without dedicated multipliers? So these count as shortcutting if the software multiplication stops if all set bits in either operand have been processed? $\endgroup$ Commented Feb 24, 2017 at 22:40
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    $\begingroup$ In many cases, the logic to detect and "shortcut" such cases would actually be slower than just doing the operation. As Chris said, it is the compiler's responsibility to minimize instructions, but for non-constant operands it may not be available. $\endgroup$ Commented Feb 24, 2017 at 23:03
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    $\begingroup$ Could you specify the type of variables (int, long, float etc)? I assume that in your case the compiler cannot determine that at compile time, right? $\endgroup$ Commented Feb 26, 2017 at 22:55