Counting bits in unsigned 64 bit using precomputation?

Revision en1, by -synx-, 2017-05-30 06:59:57

I know that counting bits using precomputation is the fastest way to go (over __builtin_popcount()).
For 32 bit integers we can do cnt[x>>16]+cnt[x&65535] by precomputing counts upto (1<<16).
How can we do it for 64 bit integers by precomputing upto (1<<22).

Tags popcount, bitwise


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en1 English -synx- 2017-05-30 06:59:57 328 Initial revision (published)