From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 2181) id 223B93857C51; Mon, 28 Nov 2022 15:19:14 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 223B93857C51 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1669648754; bh=KOm9md68TEE+I5zry5dooqFXEMjFtCuRaAIpLdyC/6E=; h=From:To:Subject:Date:From; b=lMF8oStaSZE1vmEUEeg0OFU9euU+DRLxVJtqnuJRPytN9bk8q24YU0FWcw64xpH4Z 1zGyJmCFHZhvMlDRyTCLT1U3KSsfRYCNr+hMu+0ez+F8rz3O7CO63nQ/xvf2lEX6bs 2FnKaCiT4CuZH9hSx/T3pq2PpAG7sFS5m4xu1ITE= MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="utf-8" From: Jonathan Wakely To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r13-4364] libstdc++: Make 16-bit std::subtract_with_carry_engine work [PR107466] X-Act-Checkin: gcc X-Git-Author: Jonathan Wakely X-Git-Refname: refs/heads/master X-Git-Oldrev: be7ea145514eba69a3d53340da3f05f804e48833 X-Git-Newrev: a64775a0edd46980036b757041f0c065ed9f8d22 Message-Id: <20221128151914.223B93857C51@sourceware.org> Date: Mon, 28 Nov 2022 15:19:14 +0000 (GMT) List-Id: https://gcc.gnu.org/g:a64775a0edd46980036b757041f0c065ed9f8d22 commit r13-4364-ga64775a0edd46980036b757041f0c065ed9f8d22 Author: Jonathan Wakely Date: Mon Nov 28 09:44:52 2022 +0000 libstdc++: Make 16-bit std::subtract_with_carry_engine work [PR107466] This implements the proposed resolution of LWG 3809, so that std::subtract_with_carry_engine can be used with a 16-bit result_type. Currently this produces a narrowing error when instantiating the std::linear_congruential_engine to create the initial state. It also truncates the default_seed constant when passing it as a result_type argument. Change the type of the constant to uint_least32_t and pass 0u when the default_seed should be used. libstdc++-v3/ChangeLog: PR libstdc++/107466 * include/bits/random.h (subtract_with_carry_engine): Use 32-bit type for default seed. Use 0u as default argument for subtract_with_carry_engine(result_type) constructor and seed(result_type) member function. * include/bits/random.tcc (subtract_with_carry_engine): Use 32-bit type for default seed and engine used for initial state. * testsuite/26_numerics/random/subtract_with_carry_engine/cons/lwg3809.cc: New test. Diff: --- libstdc++-v3/include/bits/random.h | 6 ++--- libstdc++-v3/include/bits/random.tcc | 4 ++-- .../subtract_with_carry_engine/cons/lwg3809.cc | 26 ++++++++++++++++++++++ 3 files changed, 31 insertions(+), 5 deletions(-) diff --git a/libstdc++-v3/include/bits/random.h b/libstdc++-v3/include/bits/random.h index 3b4e7d42bb5..523ef2d6565 100644 --- a/libstdc++-v3/include/bits/random.h +++ b/libstdc++-v3/include/bits/random.h @@ -721,9 +721,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION static constexpr size_t word_size = __w; static constexpr size_t short_lag = __s; static constexpr size_t long_lag = __r; - static constexpr result_type default_seed = 19780503u; + static constexpr uint_least32_t default_seed = 19780503u; - subtract_with_carry_engine() : subtract_with_carry_engine(default_seed) + subtract_with_carry_engine() : subtract_with_carry_engine(0u) { } /** @@ -758,7 +758,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION * set carry to 1, otherwise sets carry to 0. */ void - seed(result_type __sd = default_seed); + seed(result_type __sd = 0u); /** * @brief Seeds the initial state @f$x_0@f$ of the diff --git a/libstdc++-v3/include/bits/random.tcc b/libstdc++-v3/include/bits/random.tcc index cb1d3675783..7ec2b3f6c35 100644 --- a/libstdc++-v3/include/bits/random.tcc +++ b/libstdc++-v3/include/bits/random.tcc @@ -532,7 +532,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION subtract_with_carry_engine<_UIntType, __w, __s, __r>::long_lag; template - constexpr _UIntType + constexpr uint_least32_t subtract_with_carry_engine<_UIntType, __w, __s, __r>::default_seed; #endif @@ -541,7 +541,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION subtract_with_carry_engine<_UIntType, __w, __s, __r>:: seed(result_type __value) { - std::linear_congruential_engine + std::linear_congruential_engine __lcg(__value == 0u ? default_seed : __value); const size_t __n = (__w + 31) / 32; diff --git a/libstdc++-v3/testsuite/26_numerics/random/subtract_with_carry_engine/cons/lwg3809.cc b/libstdc++-v3/testsuite/26_numerics/random/subtract_with_carry_engine/cons/lwg3809.cc new file mode 100644 index 00000000000..21f246b8dc0 --- /dev/null +++ b/libstdc++-v3/testsuite/26_numerics/random/subtract_with_carry_engine/cons/lwg3809.cc @@ -0,0 +1,26 @@ +// { dg-do run { target c++11 } } +#include +#include + +// LWG 3809. Is std::subtract_with_carry_engine supposed to work? +// PR 107466 - invalid -Wnarrowing error with std::subtract_with_carry_engine + +int main() +{ + // It should be possible to construct this engine with a 16-bit result_type: + std::subtract_with_carry_engine s16; + std::subtract_with_carry_engine s32; + // It should have been seeded with the same sequence as the 32-bit version + // and produce random numbers in the same range, [0, 1<<12). + for (int i = 0; i < 10; ++i) + VERIFY( s16() == s32() ); + // The default seed should be usable without truncation to uint16_t: + s16.seed(); + s32.seed(); + for (int i = 0; i < 10; ++i) + VERIFY( s16() == s32() ); + s16.seed(101); + s32.seed(101); + for (int i = 0; i < 10; ++i) + VERIFY( s16() == s32() ); +}