FLS(9) Basic C Library Functions FLS(9)
NAME fls - find last set bit in word
SYNOPSIS int fls(int x);
ARGUMENTS x the word to search
DESCRIPTION This is defined in a similar way as the libc and compiler builtin ffs, but returns the position of the most significant set bit.
fls(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 32.
COPYRIGHT Kernel Hackers Manual 2.6. November 2013 FLS(9)