https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109229
Bug ID: 109229
Summary: std::exclusive_scan narrows to initial value
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: gnu-bugzilla at ribizel dot de
Target Milestone: ---
Take the following piece of code:
```
#include <vector>
#include <numeric>
#include <iostream>
#include <limits>
#include <cstdint>
int main() {
std::vector<std::int64_t> vec{1LL << 32, 0};
std::exclusive_scan(vec.begin(), vec.end(), vec.begin(), 0);
std::cout << vec[0] << '\n';
std::cout << vec[1] << '\n';
}
```
I would expect this to output 0 and 1LL<<32, but it outputs 0, 0, because T in
std::exclusive_scan is deduced as int, which is the computational type that
will be used in exclusive_scan. Not sure if this is a library or standard
defect, but I think this is pretty bug-prone otherwise. Other standard library
implementations have the same issue, see
https://github.com/NVIDIA/thrust/issues/1896 and
https://github.com/llvm/llvm-project/issues/61575.
