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Sun, 21 Jan 2024 08:35:38 -0500 X-MC-Unique: 6QUscTRTO2O8BmuI3XyQig-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (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 D89D085A588; Sun, 21 Jan 2024 13:35:37 +0000 (UTC) Received: from localhost (unknown [10.42.28.13]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9E0722166B31; Sun, 21 Jan 2024 13:35:37 +0000 (UTC) From: Jonathan Wakely To: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org Subject: [committed] libstdc++: Fix std::format floating-point alternate forms [PR113512] Date: Sun, 21 Jan 2024 13:35:15 +0000 Message-ID: <20240121133537.412487-1-jwakely@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.6 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-Spam-Status: No, score=-12.5 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_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: gcc-patches-bounces+incoming=patchwork.ozlabs.org@gcc.gnu.org Tested aarch64-linux. Pushed to trunk. Backport to gcc-13 to follow. -- >8 -- The logic for handling '#' forms was ... not good. The count of significant figures just counted digits, instead of ignoring leading zeros. And when moving the result from the stack buffer to a dynamic string the exponent could get lost in some cases. libstdc++-v3/ChangeLog: PR libstdc++/113512 * include/std/format (__formatter_fp::format): Fix logic for alternate forms. * testsuite/std/format/functions/format.cc: Check buggy cases of alternate forms with g presentation type. --- libstdc++-v3/include/std/format | 51 +++++++++++++------ .../testsuite/std/format/functions/format.cc | 6 +++ 2 files changed, 41 insertions(+), 16 deletions(-) diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format index f4d91517656..0eca8b58bfa 100644 --- a/libstdc++-v3/include/std/format +++ b/libstdc++-v3/include/std/format @@ -1623,6 +1623,7 @@ namespace __format *__p = std::toupper(*__p); } + bool __have_sign = true; // Add sign for non-negative values. if (!__builtin_signbit(__v)) { @@ -1630,56 +1631,73 @@ namespace __format *--__start = '+'; else if (_M_spec._M_sign == _Sign_space) *--__start = ' '; + else + __have_sign = false; } string_view __narrow_str(__start, __res.ptr - __start); - // Use alternate form. + // Use alternate form. Ensure decimal point is always present, + // and add trailing zeros (up to precision) for g and G forms. if (_M_spec._M_alt && __builtin_isfinite(__v)) { string_view __s = __narrow_str; - size_t __z = 0; - size_t __p; - size_t __d = __s.find('.'); - size_t __sigfigs; - if (__d != __s.npos) + size_t __sigfigs; // Number of significant figures. + size_t __z = 0; // Number of trailing zeros to add. + size_t __p; // Position of the exponent character (if any). + size_t __d = __s.find('.'); // Position of decimal point. + if (__d != __s.npos) // Found decimal point. { __p = __s.find(__expc, __d + 1); if (__p == __s.npos) __p = __s.size(); - __sigfigs = __p - 1; + + // If presentation type is g or G we might need to add zeros. + if (__trailing_zeros) + { + // Find number of digits after first significant figure. + if (__s[__have_sign] != '0') + // A string like "D.D" or "-D.DDD" + __sigfigs = __p - __have_sign - 1; + else + // A string like "0.D" or "-0.0DD". + // Safe to assume there is a non-zero digit, because + // otherwise there would be no decimal point. + __sigfigs = __p - __s.find_first_not_of('0', __d + 1); + } } - else + else // No decimal point, we need to insert one. { - __p = __s.find(__expc); + __p = __s.find(__expc); // Find the exponent, if present. if (__p == __s.npos) __p = __s.size(); __d = __p; // Position where '.' should be inserted. - __sigfigs = __d; + __sigfigs = __d - __have_sign; } if (__trailing_zeros && __prec != 0) { - if (!__format::__is_xdigit(__s[0])) - --__sigfigs; - __z = __prec - __sigfigs; // Number of zeros to insert. + // For g and G presentation types std::to_chars produces + // no more than prec significant figures. Insert this many + // zeros so the result has exactly prec significant figures. + __z = __prec - __sigfigs; } - if (size_t __extras = int(__d == __p) + __z) + if (size_t __extras = int(__d == __p) + __z) // How many to add. { if (__dynbuf.empty() && __extras <= size_t(__end - __res.ptr)) { + // The stack buffer is large enough for the result. // Move exponent to make space for extra chars. __builtin_memmove(__start + __p + __extras, __start + __p, __s.size() - __p); - if (__d == __p) __start[__p++] = '.'; __builtin_memset(__start + __p, '0', __z); __narrow_str = {__s.data(), __s.size() + __extras}; } - else + else // Need to switch to the dynamic buffer. { __dynbuf.reserve(__s.size() + __extras); if (__dynbuf.empty()) @@ -1689,6 +1707,7 @@ namespace __format __dynbuf += '.'; if (__z) __dynbuf.append(__z, '0'); + __dynbuf.append(__s.substr(__p)); } else { diff --git a/libstdc++-v3/testsuite/std/format/functions/format.cc b/libstdc++-v3/testsuite/std/format/functions/format.cc index 30c5fc22237..a27fbe74631 100644 --- a/libstdc++-v3/testsuite/std/format/functions/format.cc +++ b/libstdc++-v3/testsuite/std/format/functions/format.cc @@ -181,6 +181,12 @@ test_alternate_forms() // PR libstdc++/108046 s = std::format("{0:#.0} {0:#.1} {0:#.0g}", 10.0); VERIFY( s == "1.e+01 1.e+01 1.e+01" ); + + // PR libstdc++/113512 + s = std::format("{:#.3g}", 0.025); + VERIFY( s == "0.0250" ); + s = std::format("{:#07.3g}", 0.02); + VERIFY( s == "00.0200" ); } void