This is the mail archive of the
gcc-bugs@gcc.gnu.org
mailing list for the GCC project.
[Bug c/43756] Bit shifitng by a constant 32 isn't the same as bitshifting by a variable 32.
- From: "rguenth at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 15 Apr 2010 09:27:32 -0000
- Subject: [Bug c/43756] Bit shifitng by a constant 32 isn't the same as bitshifting by a variable 32.
- References: <bug-43756-19035@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #2 from rguenth at gcc dot gnu dot org 2010-04-15 09:27 -------
Shifting by an amount bigger than the width of the type invokes undefined
behavior (that is, target specific behavior in this case). We usually
try to simulate target behavior here but the i?86 architecture is inconsistent
in itself:
/* Define if shifts truncate the shift count
which implies one can omit a sign-extension or zero-extension
of a shift count. */
/* On i386, shifts do truncate the count. But bit opcodes don't. */
/* #define SHIFT_COUNT_TRUNCATED */
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
Summary|Bit shifitng by a constant |Bit shifitng by a constant
|32 isn't the same as |32 isn't the same as
|bitshifting by a variable |bitshifting by a variable
|32. |32.
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43756