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https://issues.apache.org/jira/browse/STDCXX-693?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12557908#action_12557908
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Martin Sebor commented on STDCXX-693:
-------------------------------------
I agree that the wording in the standard does require it, although I suspect
this interpretation was not intended (I could be wrong). GNU libstdc++ behaves
the same as stdcxx, but STLport does what you expect. The straightforward fix
is to copy the first element to the accumulator:
Index: include/valarray
===================================================================
--- include/valarray (revision 609201)
+++ include/valarray (working copy)
@@ -174,7 +174,7 @@
// 26.3.2.7, p2
value_type sum () const {
- return accumulate (_C_array.begin (), _C_array.end (), value_type ());
+ return accumulate (_C_array.begin () + 1, _C_array.end (), _C_array
[0]);
}
// 26.3.2.7, p3
Rather than implementing it, I would like to replace the use of
std::accumulate() with a simple loop like so:
Index: include/valarray
===================================================================
--- include/valarray (revision 609201)
+++ include/valarray (working copy)
@@ -173,9 +173,7 @@
}
// 26.3.2.7, p2
- value_type sum () const {
- return accumulate (_C_array.begin (), _C_array.end (), value_type ());
- }
+ value_type sum () const;
// 26.3.2.7, p3
value_type (min)() const {
Index: include/valarray.cc
===================================================================
--- include/valarray.cc (revision 609201)
+++ include/valarray.cc (working copy)
@@ -31,6 +31,18 @@
template <class _TypeT>
+_TypeT valarray<_TypeT>::sum () const
+{
+ _TypeT __sum (_C_array [0]);
+
+ for (_RWSTD_SIZE_T __i = 1; __i < _C_array.size (); ++__i)
+ __sum += _C_array [__i];
+
+ return __sum;
+}
+
+
+template <class _TypeT>
> std::valarray::sum does not work correctly for udt that has nonzero default
> value
> ---------------------------------------------------------------------------------
>
> Key: STDCXX-693
> URL: https://issues.apache.org/jira/browse/STDCXX-693
> Project: C++ Standard Library
> Issue Type: Bug
> Components: 26. Numerics
> Affects Versions: 4.2.0
> Reporter: Travis Vitek
> Priority: Minor
>
> #include <cassert>
> #include <valarray>
> struct S
> {
> // this ctor should not be required
> S ()
> : value (21)
> {
> }
> S (int v)
> : value (v)
> {
> }
> S (const S& rhs)
> : value (rhs.value)
> {
> }
> S& operator+= (const S& rhs)
> {
> value += rhs.value;
> return *this;
> }
> int value;
> };
> int main ()
> {
> const std::valarray<S> b (S (10), 1); // 10 elements with value 1
> assert (b.sum ().value == 10);
> return 0;
> }
> The wording in the standard seems to imply that the returned value should be
> a copy of one of the elements, and that op+= should be called on all of the
> other elements. If this is the case, then this an additional issue that would
> be detectable in user code [the user can count how many times the op+= is
> invoked]. This issue may apply to the min() and max() methods as well.
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