* [PATCH] PR libstdc++/87641 correctly initialize accumulator in valarray::sum()
@ 2018-10-18 16:13 Jonathan Wakely
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From: Jonathan Wakely @ 2018-10-18 16:13 UTC (permalink / raw)
To: libstdc++, gcc-patches
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Use the value of the first element as the initial value of the
__valarray_sum accumulator. Value-initialization might not create the
additive identity for the value type.
Make a similar change to __valarray_product even though it's only ever
used internally with a value_type of size_t.
PR libstdc++/87641
* include/bits/valarray_array.h (__valarray_sum): Use first element
to initialize accumulator instead of value-initializing it.
(__valarray_product<_Tp>): Move to ...
* src/c++98/valarray.cc (__valarray_product<_Tp>): Here. Use first
element to initialize accumulator.
(__valarray_product(const valarray<size_t>&)): Remove const_cast made
unnecessary by LWG 389.
* testsuite/26_numerics/valarray/87641.cc: New test.
Tested powerpc64le-linux, committed to trunk.
This seems perfectly safe so I'll backport this to the branches too,
without the changes to __valarray_product.
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commit 7b9d4da1fcf6ea3edc85ee960da1c1135614622c
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Thu Oct 18 12:32:39 2018 +0100
PR libstdc++/87641 correctly initialize accumulator in valarray::sum()
Use the value of the first element as the initial value of the
__valarray_sum accumulator. Value-initialization might not create the
additive identity for the value type.
Make a similar change to __valarray_product even though it's only ever
used internally with a value_type of size_t.
PR libstdc++/87641
* include/bits/valarray_array.h (__valarray_sum): Use first element
to initialize accumulator instead of value-initializing it.
(__valarray_product<_Tp>): Move to ...
* src/c++98/valarray.cc (__valarray_product<_Tp>): Here. Use first
element to initialize accumulator.
(__valarray_product(const valarray<size_t>&)): Remove const_cast made
unnecessary by LWG 389.
* testsuite/26_numerics/valarray/87641.cc: New test.
diff --git a/libstdc++-v3/include/bits/valarray_array.h b/libstdc++-v3/include/bits/valarray_array.h
index 6759d6003e9..2dd1ec836ac 100644
--- a/libstdc++-v3/include/bits/valarray_array.h
+++ b/libstdc++-v3/include/bits/valarray_array.h
@@ -338,33 +338,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
//
- // Compute the sum of elements in range [__f, __l)
+ // Compute the sum of elements in range [__f, __l) which must not be empty.
// This is a naive algorithm. It suffers from cancelling.
- // In the future try to specialize
- // for _Tp = float, double, long double using a more accurate
- // algorithm.
+ // In the future try to specialize for _Tp = float, double, long double
+ // using a more accurate algorithm.
//
template<typename _Tp>
inline _Tp
__valarray_sum(const _Tp* __f, const _Tp* __l)
{
- _Tp __r = _Tp();
+ _Tp __r = *__f++;
while (__f != __l)
__r += *__f++;
return __r;
}
- // Compute the product of all elements in range [__f, __l)
- template<typename _Tp>
- inline _Tp
- __valarray_product(const _Tp* __f, const _Tp* __l)
- {
- _Tp __r = _Tp(1);
- while (__f != __l)
- __r = __r * *__f++;
- return __r;
- }
-
// Compute the min/max of an array-expression
template<typename _Ta>
inline typename _Ta::value_type
diff --git a/libstdc++-v3/src/c++98/valarray.cc b/libstdc++-v3/src/c++98/valarray.cc
index 3cec1843be2..284db21e81c 100644
--- a/libstdc++-v3/src/c++98/valarray.cc
+++ b/libstdc++-v3/src/c++98/valarray.cc
@@ -45,15 +45,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template size_t valarray<size_t>::size() const;
template size_t& valarray<size_t>::operator[](size_t);
+ // Compute the product of all elements in the non-empty range [__f, __l)
+ template<typename _Tp>
+ inline _Tp
+ __valarray_product(const _Tp* __f, const _Tp* __l)
+ {
+ _Tp __r = *__f++;
+ while (__f != __l)
+ __r = __r * *__f++;
+ return __r;
+ }
+
inline size_t
__valarray_product(const valarray<size_t>& __a)
{
- const size_t __n = __a.size();
- // XXX: This ugly cast is necessary because
- // valarray::operator[]() const return a VALUE!
- // Try to get the committee to correct that gross error.
- valarray<size_t>& __t = const_cast<valarray<size_t>&>(__a);
- return __valarray_product(&__t[0], &__t[0] + __n);
+ return __valarray_product(&__a[0], &__a[0] + __a.size());
}
// Map a gslice, described by its multidimensional LENGTHS
diff --git a/libstdc++-v3/testsuite/26_numerics/valarray/87641.cc b/libstdc++-v3/testsuite/26_numerics/valarray/87641.cc
new file mode 100644
index 00000000000..eae5440e60b
--- /dev/null
+++ b/libstdc++-v3/testsuite/26_numerics/valarray/87641.cc
@@ -0,0 +1,75 @@
+// Copyright (C) 2018 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/>.
+
+#include <valarray>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+ // PR libstdc++/87641
+ std::valarray<int> v1(3);
+ v1[0] = 1;
+ v1[1] = 2;
+ v1[2] = 3;
+ std::valarray< std::valarray<int> > v2(v1, 3);
+ std::valarray<int> v3 = v2.sum();
+ VERIFY( v3.size() == v1.size() );
+ VERIFY( v3[0] == 3 );
+ VERIFY( v3[1] == 6 );
+ VERIFY( v3[2] == 9 );
+}
+
+struct X
+{
+ X() : val(1) { }
+
+ X& operator+=(const X& x) { val += x.val; return *this; }
+ bool operator==(const X& x) { return val == x.val; }
+
+ int val;
+};
+
+void
+test02()
+{
+ std::valarray<X> v1(1);
+ VERIFY( v1.sum() == v1[0] );
+
+ std::valarray<X> v2(2);
+ VERIFY( v2.sum().val == 2 );
+}
+
+struct Y
+{
+ X& operator+=(const Y&) { throw 1; }
+};
+
+void
+test03()
+{
+ std::valarray<Y> v1(1);
+ (void) v1.sum(); // no addition performed for a single element
+}
+
+int
+main()
+{
+ test01();
+ test02();
+ test03();
+}
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