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JohnnyCode

finding closest lower power of two of a integer number

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Hi,

 

I wonder how could I find closest lower power of two to a given unsigned integer. The best way would be to get the bit position of most significant bit set. But how would I find it it with as few bitwise operations as possible? I must avoid any cycle, plus, I do not want to use the look up table as I find it uninteligent.

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Yet another implementation, if you are using gcc:

unsigned round_down_to_power_of_2(unsigned x) {
  return 0x80000000u >> __builtin_clz(x);
}

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