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GET /api/patches/2226705/?format=api
{ "id": 2226705, "url": "http://patchwork.ozlabs.org/api/patches/2226705/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/patch/bmm.hhuoj2uk6c.gcc.gcc-TEST.ppalka.57.1.7@forge-stage.sourceware.org/", "project": { "id": 17, "url": "http://patchwork.ozlabs.org/api/projects/17/?format=api", "name": "GNU Compiler Collection", "link_name": "gcc", "list_id": "gcc-patches.gcc.gnu.org", "list_email": "gcc-patches@gcc.gnu.org", "web_url": null, "scm_url": null, "webscm_url": null, "list_archive_url": "", "list_archive_url_format": "", "commit_url_format": "" }, "msgid": "<bmm.hhuoj2uk6c.gcc.gcc-TEST.ppalka.57.1.7@forge-stage.sourceware.org>", "list_archive_url": null, "date": "2026-04-22T18:27:31", "name": "[v1,7/8] libstdc++: Directly implement ranges::sample [PR100795]", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "c77359f9c1d04523ef2b1e17e87f7cf4f3767878", "submitter": { "id": 93215, "url": "http://patchwork.ozlabs.org/api/people/93215/?format=api", "name": "ppalka via Sourceware Forge", "email": "forge-bot+ppalka@forge-stage.sourceware.org" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/gcc/patch/bmm.hhuoj2uk6c.gcc.gcc-TEST.ppalka.57.1.7@forge-stage.sourceware.org/mbox/", "series": [ { "id": 501079, "url": "http://patchwork.ozlabs.org/api/series/501079/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/list/?series=501079", "date": "2026-04-22T18:27:24", "name": "libstdc++: C++20 iterator awareness fixes for various Ranges algorithms [PR100795]", "version": 1, "mbox": "http://patchwork.ozlabs.org/series/501079/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2226705/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2226705/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "<gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org>", "X-Original-To": [ "incoming@patchwork.ozlabs.org", "gcc-patches@gcc.gnu.org" ], "Delivered-To": [ "patchwork-incoming@legolas.ozlabs.org", "gcc-patches@gcc.gnu.org" ], "Authentication-Results": [ "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=38.145.34.32; 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Wed, 22 Apr 2026 18:28:37 +0000 (GMT)", "from forge-stage.sourceware.org (localhost [IPv6:::1])\n (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n key-exchange x25519 server-signature ECDSA (prime256v1) server-digest SHA256)\n (No client certificate requested)\n by forge-stage.sourceware.org (Postfix) with ESMTPS id 490D8434A2\n for <gcc-patches@gcc.gnu.org>; Wed, 22 Apr 2026 18:28:35 +0000 (UTC)" ], "DKIM-Filter": [ "OpenDKIM Filter v2.11.0 sourceware.org AD2D840A130E", "OpenDKIM Filter v2.11.0 sourceware.org 8F72A48FEDB7" ], "DMARC-Filter": "OpenDMARC Filter v1.4.2 sourceware.org 8F72A48FEDB7", "ARC-Filter": "OpenARC Filter v1.0.0 sourceware.org 8F72A48FEDB7", "ARC-Seal": "i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1776882517; cv=none;\n b=PilUqfnNLHiP/Zi15mS0R6hH3WmiytKlgtclZPcH+VngpICvctGAkUT806x6NyIr4pRwAeU1bh+yCvaLzFpdwhISDlmsWUfmeJ/Q5ykcwMlDJiRH9J+MkCvP+R2Wqq3pXgotodWOOTI/xaFuzm9KziKESFreTa7cfNl7mfRhnTg=", "ARC-Message-Signature": "i=1; a=rsa-sha256; d=sourceware.org; s=key;\n t=1776882517; c=relaxed/simple;\n bh=v7OwYGZXxVhvzlL+BLSzkhqFkeisPF9kCE3Hep9fcl8=;\n h=From:Date:Subject:To:Message-ID;\n b=M2cDEPwWlrLZtriXzxaeeXEt+ys83ziTL1cETdULXMSVc05C+EorTW3Fpl2wHM7DkW4V5VF4V3GTea1GuQOdDDa5O8A5b9EHGFnKKN2VjeecRQwfGdOr5Bn+13j3c0MeiQj4dKpL4D+DAFtmCJDgwv08EtAJiVrryxUN00Kpcl0=", "ARC-Authentication-Results": "i=1; server2.sourceware.org", "From": "ppalka via Sourceware Forge\n <forge-bot+ppalka@forge-stage.sourceware.org>", "Date": "Wed, 22 Apr 2026 18:27:31 +0000", "Subject": "[PATCH v1 7/8] libstdc++: Directly implement ranges::sample\n [PR100795]", "To": "gcc-patches mailing list <gcc-patches@gcc.gnu.org>", "Message-ID": "\n <bmm.hhuoj2uk6c.gcc.gcc-TEST.ppalka.57.1.7@forge-stage.sourceware.org>", "X-Mailer": "batrachomyomachia", "X-Pull-Request-Organization": "gcc", "X-Pull-Request-Repository": "gcc-TEST", "X-Pull-Request": "https://forge.sourceware.org/gcc/gcc-TEST/pulls/57", "References": "\n <bmm.hhuoj2uk6c.gcc.gcc-TEST.ppalka.57.1.0@forge-stage.sourceware.org>", "In-Reply-To": "\n <bmm.hhuoj2uk6c.gcc.gcc-TEST.ppalka.57.1.0@forge-stage.sourceware.org>", "X-Patch-URL": "\n https://forge.sourceware.org/gcc/gcc-TEST/commit/ccd7d483f3ecd3c7832772cb18a935dbdca6b4e1", "X-BeenThere": "gcc-patches@gcc.gnu.org", "X-Mailman-Version": "2.1.30", "Precedence": "list", "List-Id": "Gcc-patches mailing list <gcc-patches.gcc.gnu.org>", "List-Unsubscribe": "<https://gcc.gnu.org/mailman/options/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=unsubscribe>", "List-Archive": "<https://gcc.gnu.org/pipermail/gcc-patches/>", "List-Post": "<mailto:gcc-patches@gcc.gnu.org>", "List-Help": "<mailto:gcc-patches-request@gcc.gnu.org?subject=help>", "List-Subscribe": "<https://gcc.gnu.org/mailman/listinfo/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=subscribe>", "Reply-To": "gcc-patches mailing list <gcc-patches@gcc.gnu.org>,\n ppalka@gcc.gnu.org", "Errors-To": "gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org" }, "content": "From: Patrick Palka <ppalka@redhat.com>\n\n\tPR libstdc++/100795\n\nlibstdc++-v3/ChangeLog:\n\n\t* include/bits/ranges_algo.h (__sample_fn::operator()):\n\tReimplement the forward_iterator branch directly.\n\t* testsuite/25_algorithms/sample/constrained.cc (test02):\n\tNew test.\n---\n libstdc++-v3/include/bits/ranges_algo.h | 70 +++++++++++++++++--\n .../25_algorithms/sample/constrained.cc | 28 ++++++++\n 2 files changed, 91 insertions(+), 7 deletions(-)", "diff": "diff --git a/libstdc++-v3/include/bits/ranges_algo.h b/libstdc++-v3/include/bits/ranges_algo.h\nindex b12da2af1263..672a0ebce0de 100644\n--- a/libstdc++-v3/include/bits/ranges_algo.h\n+++ b/libstdc++-v3/include/bits/ranges_algo.h\n@@ -1839,14 +1839,70 @@ namespace ranges\n operator()(_Iter __first, _Sent __last, _Out __out,\n \t\t iter_difference_t<_Iter> __n, _Gen&& __g) const\n {\n+\t// FIXME: Correctly handle integer-class difference types.\n \tif constexpr (forward_iterator<_Iter>)\n \t {\n-\t // FIXME: Forwarding to std::sample here requires computing __lasti\n-\t // which may take linear time.\n-\t auto __lasti = ranges::next(__first, __last);\n-\t return _GLIBCXX_STD_A::\n-\t sample(std::move(__first), std::move(__lasti), std::move(__out),\n-\t\t __n, std::forward<_Gen>(__g));\n+\t using _Size = iter_difference_t<_Iter>;\n+\t using __distrib_type = uniform_int_distribution<_Size>;\n+\t using __param_type = typename __distrib_type::param_type;\n+\t using _USize = __detail::__make_unsigned_like_t<_Size>;\n+\t using __uc_type\n+\t = common_type_t<typename remove_reference_t<_Gen>::result_type, _USize>;\n+\n+\t if (__first == __last)\n+\t return __out;\n+\n+\t __distrib_type __d{};\n+\t _Size __unsampled_sz = ranges::distance(__first, __last);\n+\t __n = std::min(__n, __unsampled_sz);\n+\n+\t // If possible, we use __gen_two_uniform_ints to efficiently produce\n+\t // two random numbers using a single distribution invocation:\n+\n+\t const __uc_type __urngrange = __g.max() - __g.min();\n+\t if (__urngrange / __uc_type(__unsampled_sz) >= __uc_type(__unsampled_sz))\n+\t // I.e. (__urngrange >= __unsampled_sz * __unsampled_sz) but without\n+\t // wrapping issues.\n+\t {\n+\t\twhile (__n != 0 && __unsampled_sz >= 2)\n+\t\t {\n+\t\t const pair<_Size, _Size> __p =\n+\t\t __gen_two_uniform_ints(__unsampled_sz, __unsampled_sz - 1, __g);\n+\n+\t\t --__unsampled_sz;\n+\t\t if (__p.first < __n)\n+\t\t {\n+\t\t\t*__out = *__first;\n+\t\t\t++__out;\n+\t\t\t--__n;\n+\t\t }\n+\n+\t\t ++__first;\n+\n+\t\t if (__n == 0) break;\n+\n+\t\t --__unsampled_sz;\n+\t\t if (__p.second < __n)\n+\t\t {\n+\t\t\t*__out = *__first;\n+\t\t\t++__out;\n+\t\t\t--__n;\n+\t\t }\n+\n+\t\t ++__first;\n+\t\t }\n+\t }\n+\n+\t // The loop above is otherwise equivalent to this one-at-a-time version:\n+\n+\t for (; __n != 0; ++__first)\n+\t if (__d(__g, __param_type{0, --__unsampled_sz}) < __n)\n+\t\t{\n+\t\t *__out = *__first;\n+\t\t ++__out;\n+\t\t --__n;\n+\t\t}\n+\t return __out;\n \t }\n \telse\n \t {\n@@ -1867,7 +1923,7 @@ namespace ranges\n \t\tif (__k < __n)\n \t\t __out[__k] = *__first;\n \t }\n-\t return __out + __sample_sz;\n+\t return __out + iter_difference_t<_Out>(__sample_sz);\n \t }\n }\n \ndiff --git a/libstdc++-v3/testsuite/25_algorithms/sample/constrained.cc b/libstdc++-v3/testsuite/25_algorithms/sample/constrained.cc\nindex b9945b164903..150e2d2036e0 100644\n--- a/libstdc++-v3/testsuite/25_algorithms/sample/constrained.cc\n+++ b/libstdc++-v3/testsuite/25_algorithms/sample/constrained.cc\n@@ -20,6 +20,7 @@\n \n #include <algorithm>\n #include <random>\n+#include <ranges>\n #include <testsuite_hooks.h>\n #include <testsuite_iterators.h>\n \n@@ -59,9 +60,36 @@ test01()\n }\n }\n \n+void\n+test02()\n+{\n+ // PR libstdc++/100795 - ranges::sample should not use std::sample\n+#if 0 // FIXME: ranges::sample rejects integer-class difference types.\n+#if __SIZEOF_INT128__\n+ auto v = std::views::iota(__int128(0), __int128(20));\n+#else\n+ auto v = std::views::iota(0ll, 20ll);\n+#endif\n+#else\n+ auto v = std::views::iota(0, 20);\n+#endif\n+\n+ int storage[20] = {2,5,4,3,1,6,7,9,10,8,11,14,12,13,15,16,18,0,19,17};\n+ auto w = v | std::views::transform([&](auto i) -> int& { return storage[i]; });\n+ using type = decltype(w);\n+ using cat = std::iterator_traits<std::ranges::iterator_t<type>>::iterator_category;\n+ static_assert( std::same_as<cat, std::output_iterator_tag> );\n+ static_assert( std::ranges::random_access_range<type> );\n+\n+ ranges::sample(v, w.begin(), 20, rng);\n+ ranges::sort(w);\n+ VERIFY( ranges::equal(w, v) );\n+}\n+\n int\n main()\n {\n test01<forward_iterator_wrapper, output_iterator_wrapper>();\n test01<input_iterator_wrapper, random_access_iterator_wrapper>();\n+ test02();\n }\n", "prefixes": [ "v1", "7/8" ] }