diff options
Diffstat (limited to 'common/alcomplex.cpp')
| -rw-r--r-- | common/alcomplex.cpp | 63 |
1 files changed, 37 insertions, 26 deletions
diff --git a/common/alcomplex.cpp b/common/alcomplex.cpp index 2675be91..ee990a39 100644 --- a/common/alcomplex.cpp +++ b/common/alcomplex.cpp @@ -44,12 +44,13 @@ struct BitReverser { /* Bit-reversal permutation applied to a sequence of fftsize items. */ for(size_t idx{1u};idx < fftsize-1;++idx) { - size_t revidx{0u}, imask{idx}; - for(size_t i{0};i < N;++i) - { - revidx = (revidx<<1) | (imask&1); - imask >>= 1; - } + size_t revidx{idx}; + revidx = ((revidx&0xaaaaaaaa) >> 1) | ((revidx&0x55555555) << 1); + revidx = ((revidx&0xcccccccc) >> 2) | ((revidx&0x33333333) << 2); + revidx = ((revidx&0xf0f0f0f0) >> 4) | ((revidx&0x0f0f0f0f) << 4); + revidx = ((revidx&0xff00ff00) >> 8) | ((revidx&0x00ff00ff) << 8); + revidx = (revidx >> 16) | ((revidx&0x0000ffff) << 16); + revidx >>= 32-N; if(idx < revidx) { @@ -62,10 +63,9 @@ struct BitReverser { } }; -/* These bit-reversal swap tables support up to 10-bit indices (1024 elements), - * which is the largest used by OpenAL Soft's filters and effects. Larger FFT - * requests, used by some utilities where performance is less important, will - * use a slower table-less path. +/* These bit-reversal swap tables support up to 11-bit indices (2048 elements), + * which is large enough for the filters and effects in OpenAL Soft. Larger FFT + * requests will use a slower table-less path. */ constexpr BitReverser<2> BitReverser2{}; constexpr BitReverser<3> BitReverser3{}; @@ -76,7 +76,8 @@ constexpr BitReverser<7> BitReverser7{}; constexpr BitReverser<8> BitReverser8{}; constexpr BitReverser<9> BitReverser9{}; constexpr BitReverser<10> BitReverser10{}; -constexpr std::array<al::span<const ushort2>,11> gBitReverses{{ +constexpr BitReverser<11> BitReverser11{}; +constexpr std::array<al::span<const ushort2>,12> gBitReverses{{ {}, {}, BitReverser2.mData, BitReverser3.mData, @@ -86,9 +87,11 @@ constexpr std::array<al::span<const ushort2>,11> gBitReverses{{ BitReverser7.mData, BitReverser8.mData, BitReverser9.mData, - BitReverser10.mData + BitReverser10.mData, + BitReverser11.mData }}; +/* Lookup table for std::polar(1, pi / (1<<index)); */ template<typename T> constexpr std::array<std::complex<T>,gBitReverses.size()-1> gArgAngle{{ {static_cast<T>(-1.00000000000000000e+00), static_cast<T>(0.00000000000000000e+00)}, @@ -101,6 +104,7 @@ constexpr std::array<std::complex<T>,gBitReverses.size()-1> gArgAngle{{ {static_cast<T>( 9.99698818696204220e-01), static_cast<T>(2.45412285229122880e-02)}, {static_cast<T>( 9.99924701839144541e-01), static_cast<T>(1.22715382857199261e-02)}, {static_cast<T>( 9.99981175282601143e-01), static_cast<T>(6.13588464915447536e-03)}, + {static_cast<T>( 9.99995293809576172e-01), static_cast<T>(3.06795676296597627e-03)} }}; } // namespace @@ -125,6 +129,9 @@ complex_fft(const al::span<std::complex<Real>> buffer, const al::type_identity_t { const size_t step2{1u << i}; const size_t step{2u << i}; + /* The first iteration of the inner loop would have u=1, which we + * can simplify to remove a number of complex multiplies. + */ for(size_t k{0};k < fftsize;k+=step) { std::complex<Real> temp{buffer[k+step2]}; @@ -150,27 +157,34 @@ complex_fft(const al::span<std::complex<Real>> buffer, const al::type_identity_t { for(size_t idx{1u};idx < fftsize-1;++idx) { - size_t revidx{0u}, imask{idx}; - for(size_t i{0};i < log2_size;++i) - { - revidx = (revidx<<1) | (imask&1); - imask >>= 1; - } + size_t revidx{idx}; + revidx = ((revidx&0xaaaaaaaa) >> 1) | ((revidx&0x55555555) << 1); + revidx = ((revidx&0xcccccccc) >> 2) | ((revidx&0x33333333) << 2); + revidx = ((revidx&0xf0f0f0f0) >> 4) | ((revidx&0x0f0f0f0f) << 4); + revidx = ((revidx&0xff00ff00) >> 8) | ((revidx&0x00ff00ff) << 8); + revidx = (revidx >> 16) | ((revidx&0x0000ffff) << 16); + revidx >>= 32-log2_size; if(idx < revidx) std::swap(buffer[idx], buffer[revidx]); } const Real pi{al::numbers::pi_v<Real> * sign}; - size_t step2{1u}; for(size_t i{0};i < log2_size;++i) { - const Real arg{pi / static_cast<Real>(step2)}; + const size_t step2{1u << i}; + const size_t step{2u << i}; + for(size_t k{0};k < fftsize;k+=step) + { + std::complex<Real> temp{buffer[k+step2]}; + buffer[k+step2] = buffer[k] - temp; + buffer[k] += temp; + } + const Real arg{pi / static_cast<Real>(step2)}; const std::complex<Real> w{std::polar(Real{1}, arg)}; - std::complex<Real> u{1.0, 0.0}; - const size_t step{step2 << 1}; - for(size_t j{0};j < step2;j++) + std::complex<Real> u{w}; + for(size_t j{1};j < step2;j++) { for(size_t k{j};k < fftsize;k+=step) { @@ -178,11 +192,8 @@ complex_fft(const al::span<std::complex<Real>> buffer, const al::type_identity_t buffer[k+step2] = buffer[k] - temp; buffer[k] += temp; } - u *= w; } - - step2 <<= 1; } } } |