Skip to content

[flang] Fix implementation of Kahan summation #116897

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Nov 21, 2024
Merged

[flang] Fix implementation of Kahan summation #116897

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 1 addition & 1 deletion flang/lib/Evaluate/fold-matmul.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -61,7 +61,7 @@ static Expr<T> FoldMatmul(FoldingContext &context, FunctionRef<T> &&funcRef) {
auto product{aElt.Multiply(bElt)};
overflow |= product.flags.test(RealFlag::Overflow);
if constexpr (useKahanSummation) {
auto next{correction.Add(product.value, rounding)};
auto next{product.value.Subtract(correction, rounding)};
overflow |= next.flags.test(RealFlag::Overflow);
auto added{sum.Add(next.value, rounding)};
overflow |= added.flags.test(RealFlag::Overflow);
Expand Down
2 changes: 1 addition & 1 deletion flang/lib/Evaluate/fold-real.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -78,7 +78,7 @@ template <int KIND> class Norm2Accumulator {
auto scaled{item.Divide(scale).value};
auto square{scaled.Multiply(scaled).value};
if constexpr (useKahanSummation) {
auto next{square.Add(correction_, rounding_)};
auto next{square.Subtract(correction_, rounding_)};
overflow_ |= next.flags.test(RealFlag::Overflow);
auto sum{element.Add(next.value, rounding_)};
overflow_ |= sum.flags.test(RealFlag::Overflow);
Expand Down
6 changes: 3 additions & 3 deletions flang/lib/Evaluate/fold-reduction.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -47,7 +47,7 @@ static Expr<T> FoldDotProduct(
const auto &rounding{context.targetCharacteristics().roundingMode()};
for (const Element &x : cProducts.values()) {
if constexpr (useKahanSummation) {
auto next{correction.Add(x, rounding)};
auto next{x.Subtract(correction, rounding)};
overflow |= next.flags.test(RealFlag::Overflow);
auto added{sum.Add(next.value, rounding)};
overflow |= added.flags.test(RealFlag::Overflow);
Expand Down Expand Up @@ -90,7 +90,7 @@ static Expr<T> FoldDotProduct(
const auto &rounding{context.targetCharacteristics().roundingMode()};
for (const Element &x : cProducts.values()) {
if constexpr (useKahanSummation) {
auto next{correction.Add(x, rounding)};
auto next{x.Subtract(correction, rounding)};
overflow |= next.flags.test(RealFlag::Overflow);
auto added{sum.Add(next.value, rounding)};
overflow |= added.flags.test(RealFlag::Overflow);
Expand Down Expand Up @@ -348,7 +348,7 @@ template <typename T> class SumAccumulator {
overflow_ |= sum.overflow;
element = sum.value;
} else { // Real & Complex: use Kahan summation
auto next{array_.At(at).Add(correction_, rounding_)};
auto next{array_.At(at).Subtract(correction_, rounding_)};
overflow_ |= next.flags.test(RealFlag::Overflow);
auto sum{element.Add(next.value, rounding_)};
overflow_ |= sum.flags.test(RealFlag::Overflow);
Expand Down
2 changes: 1 addition & 1 deletion flang/runtime/sum.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -53,7 +53,7 @@ template <typename INTERMEDIATE> class RealSumAccumulator {
}
template <typename A> RT_API_ATTRS bool Accumulate(A x) {
// Kahan summation
auto next{x + correction_};
auto next{x - correction_};
auto oldSum{sum_};
sum_ += next;
correction_ = (sum_ - oldSum) - next; // algebraically zero
Expand Down
Loading