https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125548
Bug ID: 125548
Summary: piecewise_linear_distribution(nw, xmin, xmax, fw)
invokes fw with incorrect values
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: tkaminsk at gcc dot gnu.org
Target Milestone: ---
The piecewise_linear_distribution(nw, xmin, xmax, fw) constructor invokes the
fw with incorrect values. For example with following code:
void test(int n)
{
std::cout << "Test for value " << n << std::endl;
const double step = 1.0/n;
auto test = [step, val = 0.0] (double v) mutable {
std::cout << v << " " << val << std::endl;
val += step;
return val;
};
std::piecewise_linear_distribution<> d(n, 0.0, 1.0, test);
}
The invocation of test(4) prints:
0.25 0
0.5 0.25
0.75 0.5
1 0.75
1.25 1
While standard defines (and libc++ and MVSSTL produces):
0 0
0.25 0.25
0.5 0.5
0.75 0.75
1 1
The behavior for test(1) was fixed by r17-509-g7bed7d9276c11b,
GCC-16 and eariel produces
1 0
2 1
See https://godbolt.org/z/qn84P67Md.
