[BUG]: constexpr fmod/remainder/remquo inexact for large arguments #138

Due Diligence

• I have searched for similar issues before starting this bug report

Describe the bug

The shared x - trunc(x/y)*y reduction loses the integer quotient to floating-point rounding, so the result is wrong for large |x/y|.

Steps to reproduce

#include <ccmath/ccmath.hpp>
#include <cmath>
#include <cstdio>
int main() {
  constexpr double v = ccm::fmod(1e18, 7.0);
  printf("ccm=%.17g std=%.17g\n", v, std::fmod(1e18, 7.0));
}

Output: ccm=0 std=1 (also affects remainder and the remquo remainder).

Expected behavior

fmod(1e18, 7) should be 1 (exact reduction).

Compiler version and type

Apple clang 17.0.0 (clang-1700.4.4.1)

Operating System

No response

Screenshots

Not applicable