

man ffs - jzwinck
http://linux.die.net/man/3/ffs

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jzwinck
Today I discovered ffs(3) is part of glibc. It's a family member of the GCC
extensions __builtin_clz(), _ctz(), and _ffs(), for finding the first set bit
in a word (dword, qword, multiple widths exist). See:
[http://en.wikipedia.org/wiki/Find_first_set](http://en.wikipedia.org/wiki/Find_first_set)

These functions are useful because they can be mapped to a single instruction,
BSF on x86.

