Differential D20232

Make bitpos() handle arguments with many set bits
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Authored by dougm on May 10 2019, 6:56 PM.

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kib
markj

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rS347469: When bitpos can't be implemented with an inline ffs* instruction,

Summary

When bitpos can't be implemented with an inline ffs* instruction, change the binary search so that it does not depend on a single bit only being set in the bitmask. Use bitpos more generally, and avoid some clearing of bits to accommodate its current behavior.

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dougm created this revision.May 10 2019, 6:56 PM

So why not use _Generic ?

subr_blist.c
224	Is this case ever occur ? I believe daddr_t is always 64bit. For this argument, you might actually add 'long'.

Apply _Generic instead of switch. Not previously acquainted with that construct.

dougm added inline comments.May 10 2019, 9:58 PM

subr_blist.c
224	Where I'm testing, long long and long have the same size and the switch led to a compilation error. Alan has suggested that someday he hopes to use a 32-bit daddr_t for 32-bit machines, which is why I bother sticking the int case in there.

kib added inline comments.May 10 2019, 10:17 PM

subr_blist.c
224	Did you tested with switch, or with _Generic. I would expect that you can use long with generic, since all three types 'long long', 'long' and 'int' are different, even if some of them have identical representation.