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From: "cvs-commit at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org> To: gdb-prs@sourceware.org Subject: [Bug c++/31590] (-3) >> 1 should be -2. Date: Tue, 11 Jun 2024 18:37:18 +0000 [thread overview] Message-ID: <bug-31590-4717-nkpHqYJYnH@http.sourceware.org/bugzilla/> (raw) In-Reply-To: <bug-31590-4717@http.sourceware.org/bugzilla/> https://sourceware.org/bugzilla/show_bug.cgi?id=31590 --- Comment #2 from Sourceware Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Hannes Domani <ssbssa@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=d17731525424349d7e63b517acf9f45114979fbb commit d17731525424349d7e63b517acf9f45114979fbb Author: Hannes Domani <ssbssa@yahoo.de> Date: Tue Jun 11 20:32:27 2024 +0200 Fix right shift of negative numbers PR31590 shows that right shift of negative numbers doesn't work correctly since GDB 14: (gdb) p (-3) >> 1 $1 = -1 GDB 13 and earlier returned the correct value -2. And there actually is one test that shows the failure: print -1 >> 1 $84 = 0 (gdb) FAIL: gdb.base/bitshift.exp: lang=asm: rsh neg lhs: print -1 >> 1 The problem was introduced with the change to gmp functions in commit 303a881f87. It's wrong because gdb_mpz::operator>> uses mpz_tdif_q_2exp, which always rounds toward zero, and the gmp docu says this: For positive n both mpz_fdiv_q_2exp and mpz_tdiv_q_2exp are simple bitwise right shifts. For negative n, mpz_fdiv_q_2exp is effectively an arithmetic right shift treating n as two's complement the same as the bitwise logical functions do, whereas mpz_tdiv_q_2exp effectively treats n as sign and magnitude. So this changes mpz_tdiv_q_2exp to mpz_fdiv_q_2exp, since it does right shifts for both positive and negative numbers. Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31590 Approved-By: Tom Tromey <tom@tromey.com> -- You are receiving this mail because: You are on the CC list for the bug.
next prev parent reply other threads:[~2024-06-11 18:37 UTC|newest] Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-04-02 5:57 [Bug gdb/31590] New: " tsqurt at outlook dot com 2024-04-02 12:38 ` [Bug c++/31590] " tromey at sourceware dot org 2024-05-31 11:03 ` ssbssa at sourceware dot org 2024-05-31 11:51 ` ssbssa at sourceware dot org 2024-06-11 18:37 ` cvs-commit at gcc dot gnu.org [this message] 2024-06-12 14:42 ` ssbssa at sourceware dot org 2024-07-05 19:45 ` cvs-commit at gcc dot gnu.org 2024-07-05 19:47 ` ssbssa at sourceware dot org
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