Fix Task.parallel_for_reduce on empty loop #67
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`Task.parallel_for_reduce` gives the wrong result for a the corner-case
of an empty loop with `start:0` and `finish:-1`.
For a simple (in this case: empty) loop that adds an array of 1s,
it returns `1` rather than the expected `init = 0`.
The current code builds on a reasonable assumption of non-empty parallel loops.
The PR tests for the corner-case only once per invocation ("at top-level")
and hence should not affect performance.
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Task.parallel_for_reducegives the wrong result for the corner-case of an empty loop withstart:0andfinish:-1.For a simple (in this case: empty) loop that adds an array of 1s, it returns
1rather than the expectedinit = 0.The current code builds on a reasonable assumption of non-empty parallel loops.
The PR tests for the corner-case only once per invocation ("at top-level")
and hence should not affect the performance of such loops noticeably.