Promoting of longs to long longs gives incorrect results (i.e. sign extension is not done; upper half of result may in some cases be the upper half of a previous 64-bit computation), and does not give a warning in most cases.
I have tried http://cjb.ie/32-64bug.c on the following, on various 32-bit x86 machines: gcc (GCC) 3.3.4 20040623 (Gentoo Linux 3.3.4-r1, ssp-3.3.2-2, pie-8.7.6) gcc-3.3 (GCC) 3.3.5 (Debian 1:3.3.5-8ubuntu2) gcc-3.3 (GCC) 3.3.6 (Ubuntu 1:3.3.6-8ubuntu1) gcc-4.0 (GCC) 4.0.0 20050301 (prerelease) (Debian 4.0-0pre6ubuntu7) gcc-4.0 (GCC) 4.0.2 20050808 (prerelease) (Ubuntu 4.0.1-4ubuntu9) For all of the above, and different values for -O, results seem to be invariant: $ gcc -o 32-64bug 32-64bug.c 32-64bug.c: In function âmainâ: 32-64bug.c:13: warning: left shift count >= width of type 32-64bug.c:14: warning: left shift count >= width of type $ ./32-64bug 550000000000 expected for 85LL<<40, 550000000000 obtained. 10000000000 expected for 1<<40 (const expr as printf arg), 550000000000 obtained. 10000000000 expected for 1<<40 (const expr, precomputed), 0 obtained. 5500000000000 expected for 85LL<<44, 5500000000000 obtained. 10000000000 expected for 1<<40 (variable expr, precomputed), 100 obtained. 10000000000 expected for 1<<40 (variable expr, as printf arg), 100 obtained. 55000000000000 expected for 85LL<<48, 55000000000000 obtained. 1234567800 expected for 0x12345678<<8 (const expr, as printf arg), 55000034567800 obtained. 1234567800 expected for 0x12345678<<8 (const expr, precomputed), 34567800 obtained. $ Note that a warning is only generated for the 1<<40 constant expression, and others are miscomputed with no warning. If it's not easy to get the 'expected' and 'obtained' values to match above, would it be possible to just generate a warning any time a 32-bit value is promoted to 64-bit? -- Summary: Promoting long to long long generates no warning and/or incorrect result. Product: gcc Version: 3.3.4 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: cjb at cjb dot ie GCC build triplet: i586-pc-linux-gnu GCC host triplet: i586-pc-linux-gnu GCC target triplet: i586-pc-linux-gnu http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25019
