Name
fls64 —
find last set bit in a 64-bit word
Description
This is defined in a similar way as the libc and compiler builtin
ffsll, but returns the position of the most significant set bit.
fls64(value) returns 0 if value is 0 or the position of the last
set bit if value is nonzero. The last (most significant) bit is
at position 64.