{"id":2226723,"url":"http://patchwork.ozlabs.org/api/patches/2226723/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/bmm.hhuoj2uk6c.gcc.gcc-TEST.ppalka.57.1.8@forge-stage.sourceware.org/","project":{"id":17,"url":"http://patchwork.ozlabs.org/api/projects/17/?format=json","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":"","list_archive_url":null,"date":"2026-04-22T18:27:32","name":"[v1,8/8] libstdc++: Directly implement ranges::shuffle [PR100795]","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"66709b688e66e64124fff423aab9ea0808ff603e","submitter":{"id":93215,"url":"http://patchwork.ozlabs.org/api/people/93215/?format=json","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.57.1.8@forge-stage.sourceware.org/mbox/","series":[{"id":501079,"url":"http://patchwork.ozlabs.org/api/series/501079/?format=json","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/2226723/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2226723/checks/","tags":{},"related":[],"headers":{"Return-Path":"","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=2620:52:6:3111::32; helo=vm01.sourceware.org;\n envelope-from=gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org;\n receiver=patchwork.ozlabs.org)","sourceware.org; dmarc=none (p=none dis=none)\n header.from=forge-stage.sourceware.org","sourceware.org;\n spf=pass smtp.mailfrom=forge-stage.sourceware.org","server2.sourceware.org;\n arc=none smtp.remote-ip=38.145.34.39"],"Received":["from vm01.sourceware.org (vm01.sourceware.org\n [IPv6:2620:52:6:3111::32])\n\t(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n\t key-exchange x25519 server-signature ECDSA (secp384r1) server-digest SHA384)\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4g17dw5B7gz1y2d\n\tfor ; Thu, 23 Apr 2026 04:53:08 +1000 (AEST)","from vm01.sourceware.org (localhost [127.0.0.1])\n\tby sourceware.org (Postfix) with ESMTP id DDFE140A2C74\n\tfor ; Wed, 22 Apr 2026 18:53:06 +0000 (GMT)","from forge-stage.sourceware.org (vm08.sourceware.org [38.145.34.39])\n by sourceware.org (Postfix) with ESMTPS id 8C96748FED96\n for ; 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 57E07434A3\n for ; Wed, 22 Apr 2026 18:28:35 +0000 (UTC)"],"DKIM-Filter":["OpenDKIM Filter v2.11.0 sourceware.org DDFE140A2C74","OpenDKIM Filter v2.11.0 sourceware.org 8C96748FED96"],"DMARC-Filter":"OpenDMARC Filter v1.4.2 sourceware.org 8C96748FED96","ARC-Filter":"OpenARC Filter v1.0.0 sourceware.org 8C96748FED96","ARC-Seal":"i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1776882517; cv=none;\n b=d5YBhsaBwkZuqYUXS5kxPzddD+gcCKwxTsKth3NtzukokC5ZB6Op93YMWiVBfcqcO8qDi8cnzCma4qT7/ljQB/HBceJ6cr1xhgUCk/e471PCJhv+XeBdBLVltfMYqJ1nhyfTkPxK8tptiwCK6RrA7KMRWPElNCk7Fy/yQ8J/J5k=","ARC-Message-Signature":"i=1; a=rsa-sha256; d=sourceware.org; s=key;\n t=1776882517; c=relaxed/simple;\n bh=tsU7zPesNWpEEqdIF/bcPclx4XA1cLwPbnPXKfdP9O0=;\n h=From:Date:Subject:To:Message-ID;\n b=g3MmUNTWRDqJQrAQk3IEXoCLybT0/fDr9RjRf2dIgP1XLB4uUCyvVnuOWPJgtAShLWygphmrQyE9xNva40kKvBzk+7GAY0ACN8BFwHELvdzEfkT9J7xxM9s6ANJ7csVWMBNFn5fYthvmrKLiRBydXdyJGexCwBul//X0DL4AIKs=","ARC-Authentication-Results":"i=1; server2.sourceware.org","From":"ppalka via Sourceware Forge\n ","Date":"Wed, 22 Apr 2026 18:27:32 +0000","Subject":"[PATCH v1 8/8] libstdc++: Directly implement ranges::shuffle\n [PR100795]","To":"gcc-patches mailing list ","Message-ID":"\n ","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 ","In-Reply-To":"\n ","X-Patch-URL":"\n https://forge.sourceware.org/gcc/gcc-TEST/commit/a3c5a8afc73bbf2a4e4ae14cb51119c92fc1340d","X-BeenThere":"gcc-patches@gcc.gnu.org","X-Mailman-Version":"2.1.30","Precedence":"list","List-Id":"Gcc-patches mailing list ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Reply-To":"gcc-patches mailing list ,\n ppalka@gcc.gnu.org","Errors-To":"gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org"},"content":"From: Patrick Palka \n\n\tPR libstdc++/100795\n\nlibstdc++-v3/ChangeLog:\n\n\t* include/bits/ranges_algo.h (shuffle_fn::operator()):\n\tReimplement directly.\n\t* testsuite/25_algorithms/shuffle/constrained.cc (test02):\n---\n libstdc++-v3/include/bits/ranges_algo.h | 58 ++++++++++++++++++-\n .../25_algorithms/shuffle/constrained.cc | 25 ++++++++\n 2 files changed, 80 insertions(+), 3 deletions(-)","diff":"diff --git a/libstdc++-v3/include/bits/ranges_algo.h b/libstdc++-v3/include/bits/ranges_algo.h\nindex 672a0ebce0de..83eaa7da28b9 100644\n--- a/libstdc++-v3/include/bits/ranges_algo.h\n+++ b/libstdc++-v3/include/bits/ranges_algo.h\n@@ -1952,9 +1952,61 @@ namespace ranges\n _Iter\n operator()(_Iter __first, _Sent __last, _Gen&& __g) const\n {\n-\tauto __lasti = ranges::next(__first, __last);\n-\tstd::shuffle(std::move(__first), __lasti, std::forward<_Gen>(__g));\n-\treturn __lasti;\n+\t// FIXME: Correctly handle integer-class difference types.\n+\tif (__first == __last)\n+\t return __first;\n+\n+\tusing _DistanceType = iter_difference_t<_Iter>;\n+\tusing __ud_type = __detail::__make_unsigned_like_t<_DistanceType>;\n+\tusing __distr_type = std::uniform_int_distribution<__ud_type>;\n+\tusing __p_type = typename __distr_type::param_type;\n+\n+\tusing __uc_type\n+\t = common_type_t::result_type, __ud_type>;\n+\n+\tconst __uc_type __urngrange = __g.max() - __g.min();\n+\tconst __uc_type __urange = __uc_type(__last - __first);\n+\n+\tif (__urngrange / __urange >= __urange)\n+\t // I.e. (__urngrange >= __urange * __urange) but without wrap issues.\n+\t {\n+\t _Iter __i = __first + 1;\n+\n+\t // Since we know the range isn't empty, an even number of elements\n+\t // means an uneven number of elements /to swap/, in which case we\n+\t // do the first one up front:\n+\n+\t if ((__urange % 2) == 0)\n+\t {\n+\t\t__distr_type __d{0, 1};\n+\t\tranges::iter_swap(__i++, __first + __d(__g));\n+\t }\n+\n+\t // Now we know that __last - __i is even, so we do the rest in pairs,\n+\t // using a single distribution invocation to produce swap positions\n+\t // for two successive elements at a time:\n+\n+\t while (__i != __last)\n+\t {\n+\t\tconst __uc_type __swap_range = __uc_type(__i - __first) + 1;\n+\n+\t\tconst pair<__uc_type, __uc_type> __pospos =\n+\t\t __gen_two_uniform_ints(__swap_range, __swap_range + 1, __g);\n+\n+\t\tranges::iter_swap(__i++, __first + __pospos.first);\n+\t\tranges::iter_swap(__i++, __first + __pospos.second);\n+\t }\n+\n+\t return __i;\n+\t }\n+\n+\t__distr_type __d;\n+\n+\t_Iter __i = __first + 1;\n+\tfor (; __i != __last; ++__i)\n+\t ranges::iter_swap(__i, __first + __d(__g, __p_type(0, __i - __first)));\n+\n+\treturn __i;\n }\n \n template\ndiff --git a/libstdc++-v3/testsuite/25_algorithms/shuffle/constrained.cc b/libstdc++-v3/testsuite/25_algorithms/shuffle/constrained.cc\nindex d0977a292fee..70c6bdfc3d9e 100644\n--- a/libstdc++-v3/testsuite/25_algorithms/shuffle/constrained.cc\n+++ b/libstdc++-v3/testsuite/25_algorithms/shuffle/constrained.cc\n@@ -20,6 +20,7 @@\n \n #include \n #include \n+#include \n #include \n #include \n #include \n@@ -62,8 +63,32 @@ test01()\n }\n }\n \n+void\n+test02()\n+{\n+ // PR libstdc++/100795 - ranges::shuffle should not use std::shuffle directly\n+#if 0 // FIXME: ranges::shuffle 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+ static_assert( std::ranges::random_access_range );\n+\n+ std::ranlux48_base g;\n+ ranges::shuffle(w, g);\n+}\n+\n int\n main()\n {\n test01();\n+ test02();\n }\n","prefixes":["v1","8/8"]}