tree a9d78c81a14bb9055bcfdc4b45acd284c1a93148
parent 5cab9bb5a13a26f046fe71a499696e00007d0a56
author peter klausler <pklausler@nvidia.com> 1623795558 -0700
committer Copybara-Service <copybara-worker@google.com> 1623893813 -0700

[flang] Use a "double-double" accumulator in SUM

Use a "double-double" accumulator, a/k/a Kahan summation,
in the SUM intrinsic in the runtime for real & complex.
This seems to be the best-recommended technique for reducing
error, as opposed to the initial implementation of SUM's
distinct accumulators for positive and negative items.

Differential Revision: https://reviews.llvm.org/D104338

GitOrigin-RevId: c375ec86132984bc3915323fbe3f8c71f4d5503f