Bitstring manipulation
Bitstring manipulation
The containers package contains IntMap and IntSet types which use some bit fiddling tricks to achieve very high performance.
For example -x xor x. This bit fiddling trick is especially magical because it negates an unsigned value. It would be much nicer to express the meaning of this operation in a more natural way.
One possibility I could think of would be a regex-inspired of pattern matching mechanism which could look like this:
.*10{n} -> 1*0{n+1}
This syntax is supposed to mean: "Check if the input ends in a one followed by a number n zeroes, if so produce a bitstring with all ones of the left and n+1 zeroes.
I think this is much easier to understand than the original which uses xor, but it doesn't quite feel perfect yet.
What do you think? Would you use this if it compiled to code that is as fast as the -x xor x? Do you have suggestions for improvement?
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I like the discussion, but I'm not sold on the solution :).
In particular, the {n+1} bit is not immediatly clear to me, it seems like the number of original number of bits is increasing hah!
Good point. I was thinking of transformation that preserve the length of the bitstring like if you're dealing with a type like
Word64. Otherwise perhaps you could be more specific about it like this:.{m}10{n} -> 1{m}0{n+1}