From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id 072613858C62 for ; Thu, 11 Jan 2024 23:05:53 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 072613858C62 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com ARC-Filter: OpenARC Filter v1.0.0 sourceware.org 072613858C62 Authentication-Results: server2.sourceware.org; arc=none smtp.remote-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1705014354; cv=none; b=M5ft7KJ1+bKWCqqyVKIZV443ZmxQFFid2BrwJcKOaz3gxoOmVmkAbJFvKaMBfvzbAUaEe4vRYnZcHyjj2ynTTla3cBN2TFl4TQ8fels7nswch4/9MdXXjy49Y72Hg/2alSHw6POdaZ6gPw/a7V2m98O7scPz8VR7nAFvQQ6C+vU= ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1705014354; c=relaxed/simple; bh=ZYgxak8mp9uuayccXxDfxePP9MKe90MOzFAAtT/YEu8=; h=DKIM-Signature:From:To:Subject:Date:Message-ID:MIME-Version; b=qp9OurvbS9nscraxJNKqfmH0DZvttM2k3MBnF7vZB/OQXJcVhQZaaaT+3EML1Xu/exGpU0ZaR/m7GhlL//cCImQnME50HCjyW9waGvqzWadEF8MR4vsg3HRGHyLUqVvk4yVXJP0ju+QTdUhzjcXhP+Tti4iIntZJ0zURJJiVRe8= ARC-Authentication-Results: i=1; server2.sourceware.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1705014352; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=nre+shovu/WLBZBHRJKq/lUv6xUA3/V/QhiGmFWsGhI=; b=C9DUVeve8BGc83dUzc35JpfpftPd4YsHFhf1rciNzMnSUE0QAF/Zx7jd2edZYEOE2CrpBs rBfmWMhWGHwL+kirxOyzUzSKS3RBMmBwBtwCTLQmzvqHrqxE+6cdydlWmp5nz7T5aGd6sI ANL4kdy2/GamRYJ2cZZpamdQgkXQWcs= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-183-ppPsJptZM5iWpNhyJqlODg-1; Thu, 11 Jan 2024 18:05:49 -0500 X-MC-Unique: ppPsJptZM5iWpNhyJqlODg-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 56D6C185A780; Thu, 11 Jan 2024 23:05:49 +0000 (UTC) Received: from localhost (unknown [10.42.28.185]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1F83E1C0652C; Thu, 11 Jan 2024 23:05:49 +0000 (UTC) From: Jonathan Wakely To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org Subject: [PATCH] libstdc++: Fix non-portable results from 64-bit std::subtract_with_carry_engine [PR107466] Date: Thu, 11 Jan 2024 23:04:29 +0000 Message-ID: <20240111230548.623208-1-jwakely@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.7 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-13.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H4,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: This fixes a regression introduced by the LWG 3809 change, so is needed on trunk and gcc-13 and gcc-12. Tested x86_64-linux and aarch64-linux. -- >8 -- I implemented the resolution of LWG 3809 in r13-4364-ga64775a0edd469 but more recently it was noted that the change causes possible truncation for 64-bit seeds. Whether the truncation occurs (and to what value) depends on the width of uint_least32_t which is not portable. The new problem was filed as LWG 4014. I proposed a new change which reduces the seed by the LCG's modulus before the conversion to uint_least32_t. This ensures a consistent result across paltforms, and restores the old behaviour for std::subtract_with_carry_engine specializations using a 64-bit result type (such as std::ranlux48_base). libstdc++-v3/ChangeLog: PR libstdc++/107466 * include/bits/random.tcc (subtract_with_carry_engine::seed): Implement proposed resolution of LWG 4014. * testsuite/26_numerics/random/pr60037-neg.cc: Adjust dg-error line number. * testsuite/26_numerics/random/subtract_with_carry_engine/cons/lwg3809.cc: Check for expected result of 64-bit engine with seed that doesn't fit in 32-bits. --- libstdc++-v3/include/bits/random.tcc | 5 ++++- .../26_numerics/random/pr60037-neg.cc | 2 +- .../cons/lwg3809.cc | 19 +++++++++++++++++-- 3 files changed, 22 insertions(+), 4 deletions(-) diff --git a/libstdc++-v3/include/bits/random.tcc b/libstdc++-v3/include/bits/random.tcc index 7f4bf5ea183..ade416390b3 100644 --- a/libstdc++-v3/include/bits/random.tcc +++ b/libstdc++-v3/include/bits/random.tcc @@ -541,8 +541,11 @@ _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 supposed to work? + // 4014. LWG 3809 changes behavior of some existing code std::linear_congruential_engine - __lcg(__value == 0u ? default_seed : __value); + __lcg(__value == 0u ? default_seed : __value % 2147483563u); const size_t __n = (__w + 31) / 32; diff --git a/libstdc++-v3/testsuite/26_numerics/random/pr60037-neg.cc b/libstdc++-v3/testsuite/26_numerics/random/pr60037-neg.cc index c58f480640f..59cf84adb48 100644 --- a/libstdc++-v3/testsuite/26_numerics/random/pr60037-neg.cc +++ b/libstdc++-v3/testsuite/26_numerics/random/pr60037-neg.cc @@ -12,4 +12,4 @@ auto x = std::generate_canonical #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() +// LWG 3809. Is std::subtract_with_carry_engine supposed to work? +void +test_lwg3809() { // It should be possible to construct this engine with a 16-bit result_type: std::subtract_with_carry_engine s16; @@ -24,3 +25,17 @@ int main() for (int i = 0; i < 10; ++i) VERIFY( s16() == s32() ); } + +// LWG 4014. LWG 3809 changes behavior of some existing code +void +test_lwg4014() +{ + std::ranlux48_base g(-1U + 1LL); + VERIFY( g() == 22575453646312 ); +} + +int main() +{ + test_lwg3809(); + test_lwg4014(); +} -- 2.43.0