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
