[avr-libc-dev] [bug #35496] _FFS: Macro should be obsoleted/no more recommended

[Georg-Johann Lay]

URL:
  <http://savannah.nongnu.org/bugs/?35496>

                 Summary: _FFS: Macro should be obsoleted/no more recommended
                 Project: AVR C Runtime Library
            Submitted by: gjlayde
            Submitted on: Do 09 Feb 2012 21:43:52 GMT
                Category: Library
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: libc code
                  Status: None
        Percent Complete: 0%
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 1.8.0
           Fixed Release: None

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Details:

GCC's builtin machinery can fold ffs* with constant arguments.

If a no-constant is passed to ffs resp. ffsl then avr-gcc provides efficient
assembler implementations, see __ffshi2 and __ffssi2 in libgcc:

http://gcc.gnu.org/viewcvs/trunk/libgcc/config/avr/lib1funcs.S?content-type=text%2Fplain&view=co

Notice that avr-gcc is aware of the reduces register footprint of these libgcc
functions.





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