I want to find the index of the first set bit in a bitset. Most modern CPU's can make use of the FFS instruction to speed this up on normal sized numerical types. Can I make use of this instruction when I want to find the first set bit in a C++ std::bitset?
1 Answers
The goal here is to write clear code such that the optimizer recognises the operation. It probably knows about ffs and when to use it.
A fixed-size array helps, it gives constants in the loop which facilitates unrolling. Alignment also looks in your favour.
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