On 28/08/20 23:11 +0100, Jonathan Wakely wrote:
This fixes a bug with mixed signed and unsigned types, where converting
a negative value to the unsigned result type alters the value. The
solution is to obtain the absolute values of the arguments immediately
and to perform the actual GCD or LCM algorithm on two arguments of the
same type.
In order to operate on the most negative number without overflow when
taking its absolute, use an unsigned type for the result of the abs
operation. For example, -INT_MIN will overflow, but -(unsigned)INT_MIN
is (unsigned)INT_MAX+1U which is the correct value.
libstdc++-v3/ChangeLog:
PR libstdc++/92978
* include/std/numeric (__abs_integral): Replace with ...
(__detail::__absu): New function template that returns an
unsigned type, guaranteeing it can represent the most
negative signed value.
(__detail::__gcd, __detail::__lcm): Require arguments to
be unsigned and therefore already non-negative.
(gcd, lcm): Convert arguments to absolute value as unsigned
type before calling __detail::__gcd or __detail::__lcm.
* include/experimental/numeric (gcd, lcm): Likewise.
* testsuite/26_numerics/gcd/gcd_neg.cc: Adjust expected
errors.
* testsuite/26_numerics/lcm/lcm_neg.cc: Likewise.
* testsuite/26_numerics/gcd/92978.cc: New test.
* testsuite/26_numerics/lcm/92978.cc: New test.
* testsuite/experimental/numeric/92978.cc: New test.
Tested powerpc64le-linux. Committed to trunk.
[snip]
diff --git a/libstdc++-v3/testsuite/experimental/numeric/92978.cc
b/libstdc++-v3/testsuite/experimental/numeric/92978.cc
new file mode 100644
index 00000000000..8408fd4d9ce
--- /dev/null
+++ b/libstdc++-v3/testsuite/experimental/numeric/92978.cc
@@ -0,0 +1,48 @@
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3. If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do compile { target c++14 } }
+
+#include <experimental/numeric>
+#include <limits.h>
+
+void
+test01()
+{
+ // PR libstdc++/92978
+ static_assert( std::experimental::gcd(-120, 10U) == 10,
+ "mixed signed/unsigned" );
+ static_assert( std::experimental::gcd(120U, -10) == 10,
+ "mixed signed/unsigned" );
+
+ static_assert( std::lcm(-42, 21U) == 42U );
This test is supposed to be usingthe experimental functions, but this
calls std::lcm (and so the test fails if run as C++14).
Fixed with the attached patch, committed to trunk.
commit c71644776f4e8477289a4de16239dbb420db6945
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Wed Sep 2 17:20:37 2020
libstdc++: Fix test to use correct function
This was copied from a test for std::lcm but I forgot to change one of
the calls to use the experimental version of the function.
libstdc++-v3/ChangeLog:
PR libstdc++/92978
* testsuite/experimental/numeric/92978.cc: Use experimental::lcm
not std::lcm.
diff --git a/libstdc++-v3/testsuite/experimental/numeric/92978.cc b/libstdc++-v3/testsuite/experimental/numeric/92978.cc
index 8408fd4d9ce..e2a4b1adefa 100644
--- a/libstdc++-v3/testsuite/experimental/numeric/92978.cc
+++ b/libstdc++-v3/testsuite/experimental/numeric/92978.cc
@@ -29,7 +29,7 @@ test01()
static_assert( std::experimental::gcd(120U, -10) == 10,
"mixed signed/unsigned" );
- static_assert( std::lcm(-42, 21U) == 42U );
+ static_assert( std::experimental::lcm(-42, 21U) == 42U );
}
void
