https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70299
Bug ID: 70299
Summary: pow(long double, int) gives more imprecise result than
pow(long double,long double) in c++03 mode
Product: gcc
Version: 5.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: b7.10110111 at gmail dot com
Target Milestone: ---
The following example program appears to get different results for different
overloads of std::pow(), even though all the parameters don't lose precision on
call:
#include <iostream>
#include <cmath>
#include <limits>
int main()
{
std::cout.precision(std::numeric_limits<long double>::digits10+3); //
=max_digits10
std::cout << "pow(long double, int) : " << std::pow(10.L,-4823) <<
"\n";
std::cout << "pow(long double, long double): " << std::pow(10.L,-4823.L) <<
"\n";
}
Its output in -std=c++03 mode:
pow(long double, int) : 1.00000000000000000288e-4823
pow(long double, long double): 1.00000000000000000005e-4823
And in -std=c++11 and -std=c++14 mode it's correct:
pow(long double, int) : 1.00000000000000000005e-4823
pow(long double, long double): 1.00000000000000000005e-4823
