From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 8708E3857003; Thu, 25 Feb 2021 13:09:56 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 8708E3857003 From: "spoettl at hotmail dot com" To: gcc-bugs@gcc.gnu.org Subject: [Bug c/99268] New: shifted uint64_t becomes wrong value Date: Thu, 25 Feb 2021 13:09:56 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: c X-Bugzilla-Version: 10.2.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: spoettl at hotmail dot com X-Bugzilla-Status: UNCONFIRMED X-Bugzilla-Resolution: X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status bug_severity priority component assigned_to reporter target_milestone Message-ID: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: gcc-bugs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-bugs mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 25 Feb 2021 13:09:56 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99268 Bug ID: 99268 Summary: shifted uint64_t becomes wrong value Product: gcc Version: 10.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: spoettl at hotmail dot com Target Milestone: --- MY COMPILER VERSION =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D stefan@Apollon:~$ gcc -v Using built-in specs. COLLECT_GCC=3Dgcc COLLECT_LTO_WRAPPER=3D/usr/lib/gcc/x86_64-linux-gnu/10/lto-wrapper OFFLOAD_TARGET_NAMES=3Dnvptx-none:amdgcn-amdhsa:hsa OFFLOAD_TARGET_DEFAULT=3D1 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion=3D'Ubuntu 10.2.0-13ubuntu1' --with-bugurl=3Dfile:///usr/share/doc/gcc-10/README.Bugs --enable-languages=3Dc,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix= =3D/usr --with-gcc-major-version-only --program-suffix=3D-10 --program-prefix=3Dx86_64-linux-gnu- --enable-shared --enable-linker-build-= id --libexecdir=3D/usr/lib --without-included-gettext --enable-threads=3Dposix --libdir=3D/usr/lib --enable-nls --enable-clocale=3Dgnu --enable-libstdcxx-= debug --enable-libstdcxx-time=3Dyes --with-default-libstdcxx-abi=3Dnew --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib --enable-libphobos-checking=3Drelea= se --with-target-system-zlib=3Dauto --enable-objc-gc=3Dauto --enable-multiarch --disable-werror --with-arch-32=3Di686 --with-abi=3Dm64 --with-multilib-list=3Dm32,m64,mx32 --enable-multilib --with-tune=3Dgeneric --enable-offload-targets=3Dnvptx-none=3D/build/gcc-10-JvwpWM/gcc-10-10.2.0/= debian/tmp-nvptx/usr,amdgcn-amdhsa=3D/build/gcc-10-JvwpWM/gcc-10-10.2.0/deb= ian/tmp-gcn/usr,hsa --without-cuda-driver --enable-checking=3Drelease --build=3Dx86_64-linux-gnu --host=3Dx86_64-linux-gnu --target=3Dx86_64-linux-gnu Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 10.2.0 (Ubuntu 10.2.0-13ubuntu1)=20 PROGRAMM PRODUCING (UNEXPECTED) WRONG VALUES BY SHIFTING UINT64_T =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D #include #include typedef uint8_t N8; typedef uint16_t N16; typedef uint32_t N32; typedef uint64_t N64; // Counting the number of bits in n // (leading zeros are not counted) N8 numberBits(N64 n) { N8 b =3D 1, lz =3D 0; // The compiler doesn't like 1 << 63! // (such that the most significant bit of n is set) N64 mk =3D 1 << 31; mk <<=3D 31; mk <<=3D 1; if (n > 0) { while ((n & mk) =3D=3D 0) { lz++; mk >>=3D 1; } b =3D 64 - lz; } return b; } void numberBitsTest() { N64 n; // Working Code: n =3D 1; printf("%lu has %2i bits\n", n, numberBits(n)); n =3D 1 << 17; printf("%lu has %2i bits\n", n, numberBits(n)); // Now the bug: n =3D 1 << 31; printf("n was set to (1 << 31) =3D=3D 2**32\n"); printf("%lu has %2i bits\n", n, numberBits(n)); printf("Hexadecimal:\n"); printf("%lX has %2i bits\n", n, numberBits(n)); // Doen't disappear for bigger n: n <<=3D 30; printf("n was set to (1 << 61) =3D=3D 2**62\n"); printf("%lu has %2i bits\n", n, numberBits(n)); printf("Hexadecimal:\n"); printf("%lX has %2i bits\n", n, numberBits(n));=20=20=20=20 } int main() { numberBitsTest(); return 0; }=