http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50481
Bug #: 50481
Summary: builtin to reverse the bit order
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: middle-end
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: marc.gli...@normalesup.org
It would be useful if gcc provided a builtin to reverse the order of the bits
(turn abcdefgh into hgfedcba) in objects of all sizes from a byte to an
unsigned long long.
According to Joseph: "Various processors have an instruction to reverse the bit
order in a word (ARMv6T2 and later have RBIT, for example, and C6X has BITR on
C64X and above)." This kind of bit manipulation also has various optimizations
depending on the architecture (mirroring a byte can be implemented using a
64bit multiplication). It is thus well suited to a builtin with different
platform-specific implementations.
Such a builtin could be used for instance for Bug 50160.
