[Bug fortran/37635] New: Fortran 2008: Support LEADZ / TRAILZ

["burnus at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

Requested by Richard Townsend at
http://groups.google.com/group/comp.lang.fortran/browse_thread/thread/1e4130b9720e4f2a

LEADZ and TRAILZ are rather common vendor extensions, e.g. supported by the
Intel compiler (it also allows for logical arguments).

LEADZ (I)
  Description. Number of leading zero bits.
  Argument. I shall be of type integer.
  Result Value. If all of the bits of I are zero, the result value is
                BIT SIZE (I). [...]

TRAILZ (I)
  Description. Number of trailing zero bits.
  Argument. I shall be of type integer.


The implementation should be relatively easy using the following built-ins,
however, one presumably needs a special case for ZERO.

 BUILT_IN_CLZ*
 "These functions return the number of leading 0-bits in a, starting
  at the most significant bit position. If a is zero, the result
  is undefined."
and
 BUILT_IN_CTZ*
 "These functions return the number of trailing 0-bits in a, starting at the 
  least significant bit position. If a is zero, the result is undefined."
(Description copied from
http://gcc.gnu.org/onlinedocs/gccint/Integer-library-routines.html)

For compile-time simplification, MPFR does not seem to provide a ready-to-use
function; if one cooks up something oneself, one needs to check endian issues
(though there might be none).


-- 
           Summary: Fortran 2008: Support LEADZ / TRAILZ
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: burnus at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37635