8000 GH-100425: Improve accuracy of builtin sum() for float inputs by rhettinger · Pull Request #100426 · python/cpython · GitHub
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GH-100425: Improve accuracy of builtin sum() for float inputs #100426

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Merged
merged 13 commits into from
Dec 23, 2022
Merged

GH-100425: Improve accuracy of builtin sum() for float inputs #100426

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916ab7e
Neumaier compensated summation
rhettinger Dec 22, 2022
787f2e5
Kahan summation
rhettinger Dec 22, 2022
bc308aa
Revert "Kahan summation"
rhettinger Dec 22, 2022
0c2ba04
Restore the bogus sign tests
rhettinger Dec 22, 2022
89e46c8
Add tests and comments
rhettinger Dec 22, 2022
a9cb7d2
Add tests and docs
rhettinger Dec 22, 2022
839cc05
Add blurb
rhettinger Dec 22, 2022
66db937
Remove out of date example for fsum()
rhettinger Dec 22, 2022
af7613e
Update floating point tutorial
rhettinger Dec 22, 2022
4f4b731
Correct handling of overflowed or infinite sums
rhettinger Dec 23, 2022
4da0b8f
Move local declarations inside the block where they are used.
rhettinger Dec 23, 2022
6c7894c
For consistent results, apply compensation on the slow path as well.
rhettinger Dec 23, 2022
3cf9536
Mark as an implementation detail.
rhettinger Dec 23, 2022
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Move local declarations inside the block where they are used.
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@rhettinger
rhettinger committed Dec 23, 2022
commit 4da0b8ff2e83ecea46bab85d56850851ea3c7eec
5 changes: 2 additions & 3 deletions Python/bltinmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2533,7 +2533,6 @@ builtin_sum_impl(PyObject *module, PyObject *iterable, PyObject *start)
if (PyFloat_CheckExact(result)) {
double f_result = PyFloat_AS_DOUBLE(result);
double c = 0.0;
double x, t;
Py_SETREF(result, NULL);
while(result == NULL) {
item = PyIter_Next(iter);
Expand All @@ -2552,8 +2551,8 @@ builtin_sum_impl(PyObject *module, PyObject *iterable, PyObject *start)
if (PyFloat_CheckExact(item)) {
// Improved Kahan–Babuška algorithm by Arnold Neumaier
// https://www.mat.univie.ac.at/~neum/scan/01.pdf
x = PyFloat_AS_DOUBLE(item);
t = f_result + x;
double x = PyFloat_AS_DOUBLE(item);
double t = f_result + x;
if (fabs(f_result) >= fabs(x)) {
c += (f_result - t) + x;
} else {
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