Created
September 6, 2016 22:20
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template < | |
bool Inv, | |
std::ptrdiff_t N_out | |
> | |
inline void | |
butterfly_radix4(gsl::span<cpx_t, N_out> output) | |
const noexcept { | |
auto const m = N_out/4; | |
auto const stride = (N_out > 0) ? N / N_out : 0; | |
std::swap(output[1*m], output[2*m]); | |
std::tie(output[0*m], output[1*m]) = math::scissors(output[0*m], output[1*m]); | |
std::tie(output[2*m], output[3*m]) = math::scissors(output[2*m], output[3*m]); | |
std::tie(output[0*m], output[2*m]) = math::scissors(output[0*m], output[2*m]); | |
output[3*m] = flip<Inv>(output[3*m]); | |
std::tie(output[1*m], output[3*m]) = math::scissors(output[1*m], output[3*m]); | |
for (auto i = 1; i < m; ++i) { | |
std::swap(output[1*m], output[2*m]); | |
output[1*m] = math::multiply_fast(output[1*m], twiddle<Inv>(2*i * stride)); | |
output[2*m] = math::multiply_fast(output[2*m], twiddle<Inv>(1*i * stride)); | |
output[3*m] = math::multiply_fast(output[3*m], twiddle<Inv>(3*i * stride)); | |
std::tie(output[0*m], output[1*m]) = math::scissors(output[0*m], output[1*m]); | |
std::tie(output[2*m], output[3*m]) = math::scissors(output[2*m], output[3*m]); | |
std::tie(output[0*m], output[2*m]) = math::scissors(output[0*m], output[2*m]); | |
output[3*m] = flip<Inv>(output[3*m]); | |
std::tie(output[1*m], output[3*m]) = math::scissors(output[1*m], output[3*m]); | |
} | |
} |
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