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Could we have a find_prev() as well? #102
Description
Hi! Could we have a find_prev() to go along the find_next()? That would allow efficient reverse iteration over all 1-bits. The code should be pretty much the reverse of find_next(), and using countl_zero instead of countr_zero as the bit intrinsic function.
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gennaroprota commentedon Jan 5, 2026
Hi Rein! Thanks for the suggestion :-).
Apparently, some people are confused by the name of
find_first_off()(they mix it up withfind_first_of(), although the latter wouldn't make much sense for a bitset), so I'm thinking of the following renames:find_first()→find_first_one()find_first_off()→find_first_zero()find_next()→find_next_one()find_next_off()→find_next_zero()Once I have decided on that, I'll implement the member you suggested. It will likely be named
find_previous_one().gennaroprota commentedon Jan 9, 2026
@rhalbersma: I sketched an implementation in PR #103. It adds a
find_last_one(), too, although that's logically unnecessary, because ab.find_previous_one( i )withi >= b.size()(e.g.i == npos) would find the last 1 bit. Please let me know what you think.gennaroprota commentedon Apr 28, 2026
This has been open for a long time without feedback. Going to close it.