Function cos_reduce_

src/fl/math/math.cpp.hpp:202–206

template <typename F>
inline F cos_reduce_(F x) FL_NOEXCEPT {
    // cos(x) = sin(π/2 - x)
    const F kPiHalf = F(1.57079632679489661923);
    return sin_reduce_(kPiHalf - x);
}

// --- log via fraction extraction + polynomial -----------------------------
//