wash added a comment.
Here's `partial_sum`:
template <class _InputIterator, class _OutputIterator, class _BinaryOperation>
inline _LIBCPP_INLINE_VISIBILITY
_OutputIterator
partial_sum(_InputIterator __first, _InputIterator __last, _OutputIterator
__result,
_BinaryOperation __binary_op)
{
if (__first != __last)
{
typename iterator_traits<_InputIterator>::value_type __t(*__first);
*__result = __t;
for (++__first, (void) ++__result; __first != __last; ++__first,
(void) ++__result)
{
__t = __binary_op(__t, *__first);
*__result = __t;
}
}
return __result;
}
And here's the `inclusive_scan` that should be equivalent to that `partial_sum`:
template <class _InputIterator, class _OutputIterator, class _BinaryOp>
inline _LIBCPP_INLINE_VISIBILITY
_OutputIterator
inclusive_scan(_InputIterator __first, _InputIterator __last,
_OutputIterator __result, _BinaryOp __b)
{
if (__first != __last) {
typename iterator_traits<_InputIterator>::value_type __init =
*__first++;
return inclusive_scan(__first, __last, __result, __b, __init);
}
return __result;
}
The `inclusive_scan` that it forwards to is:
template <class _InputIterator, class _OutputIterator, class _Tp, class
_BinaryOp>
inline _LIBCPP_INLINE_VISIBILITY
_OutputIterator
inclusive_scan(_InputIterator __first, _InputIterator __last,
_OutputIterator __result, _BinaryOp __b, _Tp __init)
{
*__result++ = __init;
for (; __first != __last; ++__first) {
__init = __b(__init, *__first);
*__result++ = __init;
}
return __result;
}
Inlining it, we get:
template <class _InputIterator, class _OutputIterator, class _BinaryOp>
inline _LIBCPP_INLINE_VISIBILITY
_OutputIterator
inclusive_scan(_InputIterator __first, _InputIterator __last,
_OutputIterator __result, _BinaryOp __b)
{
if (__first != __last) {
typename iterator_traits<_InputIterator>::value_type __init =
*__first++;
*__result++ = __init;
for (; __first != __last; ++__first) {
__init = __b(__init, *__first);
*__result++ = __init;
}
}
return __result;
}
That looks equivalent to the `partial_sum` implementation above, so I think it
is correct.
https://reviews.llvm.org/D34007
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