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    <p>As John said numbers with a decimal place default to double. TomTom is wrong.</p> <p>I was curious to know if the compiler would just optimize the double to a const float (which I assumed would happen)... turns out it doesn't and the idea of the speed increase is actually legit... depending on how much you use it. In math-heavy application, you probably do want to use this trick.</p> <p>It must be the case that it is taking the stored float variable, casting it to a double, performing the math against the double (the number without the f), then casting it back to a float to store it again. That would explain the diference in calculation even though we're storing in floats each time.</p> <p>The code &amp; raw results: <a href="https://gist.github.com/1880400" rel="nofollow">https://gist.github.com/1880400</a></p> <p>Pulled out relevant benchmark on an iPad 1 in Debug profile (Release resulted in even more of a performance <em>increase</em> by using the f notation):</p> <pre> ------------ 10000000 total loops timeWithDoubles: 1.33593 sec timeWithFloats: 0.80924 sec Float speed up: 1.65x Difference in calculation: -0.000038 </pre> <p>Code:</p> <pre><code>int main (int argc, const char * argv[]) { for (unsigned int magnitude = 100; magnitude &lt; INT_MAX; magnitude *= 10) { runTest(magnitude); } return 0; } void runTest(int numIterations) { NSTimeInterval startTime = CFAbsoluteTimeGetCurrent(); float d = 1.2f; for (int i = 0; i &lt; numIterations; i++) { d += 1.8368383; d *= 0.976; } NSTimeInterval timeWithDoubles = CFAbsoluteTimeGetCurrent() - startTime; startTime = CFAbsoluteTimeGetCurrent(); float f = 1.2f; for (int i = 0; i &lt; numIterations; i++) { f += 1.8368383f; f *= 0.976f; } NSTimeInterval timeWithFloats = CFAbsoluteTimeGetCurrent() - startTime; printf("\n------------ %d total loops\n", numIterations); printf("timeWithDoubles: %2.5f sec\n", timeWithDoubles); printf("timeWithFloats: %2.5f sec\n", timeWithFloats); printf("Float speed up: %2.2fx\n", timeWithDoubles / timeWithFloats); printf("Difference in calculation: %f\n", d - f); } </code></pre>
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    1. PODo I need to use decimal places when using floats? Is the "f" suffix necessary?
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