unsigned long ccNextPOT(unsigned long x){
x = x - 1;
x = x | (x >> 1);
x = x | (x >> 2);
x = x | (x >> 4);
x = x | (x >> 8);
x = x | (x >>16);
return x + 1;
}
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i know it works well, but i want to know which algorithm it use. – guoxx Dec 26 '11 at 15:51
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3Have a look [here](http://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2). – Howard Dec 26 '11 at 15:51
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Possible duplicate of [Rounding up to next power of 2](https://stackoverflow.com/questions/466204/rounding-up-to-next-power-of-2) – phuclv Jul 19 '18 at 03:18
1 Answers
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The OR and SHIFT statements fills with ones all bits of x to the right of most significant bit (up to 32 bits). Together with the pre-decrement and post-increment statements, this computes (as the function name suggets) the next power-of-two number, equal or greater than the given number (if x is greater than 0 and less than 2^32)
leonbloy
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The pre-decrement ensures inputs of zero and powers of two are mapped onto themselves. – njuffa Dec 26 '11 at 17:41