[issue38992] testFsum failure caused by constant folding of a float expression

[Mark Dickinson]

Mark Dickinson <dickinsm at gmail.com> added the comment:

Note that the exact values of `1.7**i` don't matter here - some sloppiness in the `pow` results should not cause a test failure. The key point is that under fairly mild assumptions about IEEE 754 conformance, the subtractions `1.7**(i+1) - 1.7**i` are always performed exactly, thanks to Sterbenz's lemma.

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<https://bugs.python.org/issue38992>
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