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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug libstdc++/107466] [12 Regression] invalid -Wnarrowing error with std::subtract_with_carry_engine Date: Thu, 11 Jan 2024 13:34:55 +0000 [thread overview] Message-ID: <bug-107466-4-96r30TKyUM@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-107466-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107466 Jonathan Wakely <redi at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|RESOLVED |REOPENED Resolution|FIXED |--- --- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> --- I'm reopening this because the fix changes the behaviour of some code: https://cplusplus.github.io/LWG/issue4014 As noted there, std::ranlux48_base(UINT_MAX+1LL)() changed behaviour. Originally that yielded 22575453646312 but after the commits above it yields 23223501020940 This is what I proposed for 4014 and restores the original behaviour: --- a/libstdc++-v3/include/bits/random.tcc +++ b/libstdc++-v3/include/bits/random.tcc @@ -541,8 +541,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION subtract_with_carry_engine<_UIntType, __w, __s, __r>:: seed(result_type __value) { + // _GLIBCXX_RESOLVE_LIB_DEFECTS + // 3809. Is std::subtract_with_carry_engine<uint16_t> supposed to work? + // 4014. LWG 3809 changes behavior of some existing code + if (__value == 0u) + __value = default_seed; + else + __value %= 2147483563u; + std::linear_congruential_engine<uint_least32_t, 40014u, 0u, 2147483563u> - __lcg(__value == 0u ? default_seed : __value); + __lcg(__value); const size_t __n = (__w + 31) / 32;
next prev parent reply other threads:[~2024-01-11 13:34 UTC|newest] Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-10-30 18:42 [Bug c++/107466] New: [12 Regression] invalid -Wnarrowing error littlefox+gcc-bugzilla@lf-net.org 2022-10-30 18:50 ` [Bug c++/107466] [12/13 Regression] invalid -Wnarrowing error with std::subtract_with_carry_engine pinskia at gcc dot gnu.org 2022-10-30 20:40 ` redi at gcc dot gnu.org 2022-10-31 17:40 ` littlefox+gcc-bugzilla@lf-net.org 2022-11-04 20:39 ` [Bug libstdc++/107466] " redi at gcc dot gnu.org 2022-11-05 10:26 ` rguenth at gcc dot gnu.org 2022-11-25 9:38 ` redi at gcc dot gnu.org 2022-11-28 15:19 ` cvs-commit at gcc dot gnu.org 2023-04-27 11:42 ` [Bug libstdc++/107466] [12 " rguenth at gcc dot gnu.org 2023-04-27 11:42 ` rguenth at gcc dot gnu.org 2023-04-27 14:43 ` cvs-commit at gcc dot gnu.org 2023-04-27 14:44 ` redi at gcc dot gnu.org 2024-01-11 13:34 ` redi at gcc dot gnu.org [this message] 2024-01-13 0:14 ` cvs-commit at gcc dot gnu.org 2024-02-08 15:51 ` cvs-commit at gcc dot gnu.org 2024-02-08 21:28 ` cvs-commit at gcc dot gnu.org 2024-02-08 21:42 ` redi at gcc dot gnu.org
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