[Feature] std::bit::leadcount() #2503
Description
What feature would you like to see?
Similar to popcount in that it counts set bits, but only counts the consecutive leading bits of the given integer/bitfield(?).
i.e.:
0b00000001 => 0
0b10000001 => 1
0b11000001 => 2
...
0b11111101 => 6
0b11111110 => 7
0b11111111 => 8
Perhaps std::bit::trailcount() for trailing ones could also be added?
How will this feature be useful to you and others?
Some variable-integer encodings, like the one UTF-8 is built on, use the leadcount to determine the amount of bytes to read in advance (instead of a while((byte=read()) & 0x80 != 0)-loop), which is just easier to work with... and removes a branch misprediction! ;)
Request Type
- I can provide a PoC for this feature or am willing to work on it myself and submit a PR
Additional context?
This could be implemented on top of popcount with some bit-twiddling in a pattern function... but with how basic it is, it ought to be in the stdlib.