https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66346
Bug ID: 66346
Summary: GCC computes log10(2.L) constant wrongly
Product: gcc
Version: 5.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: b7.10110111 at gmail dot com
Target Milestone: ---
Consider the following code:
#include <iostream>
#include <cmath>
int main()
{
volatile long double two=2.L;
long double vol=log10(two);
long double con=log10(2.L);
long double ref=0.3010299956639811952L;
std::cout.precision(19);
std::cout << "computed constant: " << con << '\n';
std::cout << "computed volatile: " << vol << '\n';
std::cout << "reference value : " << ref << "\n";
}
Here reference value was computed using Wolfram Mathematica via N[Log10[2],19]
command.
On x86 system it this code, compiled with gcc 4.5, 4.8, 4.9 and 5.1, gives me
this output:
computed constant: 0.301029995663981198
computed volatile: 0.3010299956639811952
reference value : 0.3010299956639811952
On x86_64 system it prints this:
computed constant: 0.301029995663981198
computed volatile: 0.301029995663981198
reference value : 0.3010299956639811952
This appears to be wrong result. The same code compiled by clang++ 3.0.6ubuntu3
gives all values equal to reference value.
