Antonio Sanchez
bde6741641
Improved std::complex sqrt and rsqrt.
...
Replaces `std::sqrt` with `complex_sqrt` for all platforms (previously
`complex_sqrt` was only used for CUDA and MSVC), and implements
custom `complex_rsqrt`.
Also introduces `numext::rsqrt` to simplify implementation, and modified
`numext::hypot` to adhere to IEEE IEC 6059 for special cases.
The `complex_sqrt` and `complex_rsqrt` implementations were found to be
significantly faster than `std::sqrt<std::complex<T>>` and
`1/numext::sqrt<std::complex<T>>`.
Benchmark file attached.
```
GCC 10, Intel Xeon, x86_64:
---------------------------------------------------------------------------
Benchmark Time CPU Iterations
---------------------------------------------------------------------------
BM_Sqrt<std::complex<float>> 9.21 ns 9.21 ns 73225448
BM_StdSqrt<std::complex<float>> 17.1 ns 17.1 ns 40966545
BM_Sqrt<std::complex<double>> 8.53 ns 8.53 ns 81111062
BM_StdSqrt<std::complex<double>> 21.5 ns 21.5 ns 32757248
BM_Rsqrt<std::complex<float>> 10.3 ns 10.3 ns 68047474
BM_DivSqrt<std::complex<float>> 16.3 ns 16.3 ns 42770127
BM_Rsqrt<std::complex<double>> 11.3 ns 11.3 ns 61322028
BM_DivSqrt<std::complex<double>> 16.5 ns 16.5 ns 42200711
Clang 11, Intel Xeon, x86_64:
---------------------------------------------------------------------------
Benchmark Time CPU Iterations
---------------------------------------------------------------------------
BM_Sqrt<std::complex<float>> 7.46 ns 7.45 ns 90742042
BM_StdSqrt<std::complex<float>> 16.6 ns 16.6 ns 42369878
BM_Sqrt<std::complex<double>> 8.49 ns 8.49 ns 81629030
BM_StdSqrt<std::complex<double>> 21.8 ns 21.7 ns 31809588
BM_Rsqrt<std::complex<float>> 8.39 ns 8.39 ns 82933666
BM_DivSqrt<std::complex<float>> 14.4 ns 14.4 ns 48638676
BM_Rsqrt<std::complex<double>> 9.83 ns 9.82 ns 70068956
BM_DivSqrt<std::complex<double>> 15.7 ns 15.7 ns 44487798
Clang 9, Pixel 2, aarch64:
---------------------------------------------------------------------------
Benchmark Time CPU Iterations
---------------------------------------------------------------------------
BM_Sqrt<std::complex<float>> 24.2 ns 24.1 ns 28616031
BM_StdSqrt<std::complex<float>> 104 ns 103 ns 6826926
BM_Sqrt<std::complex<double>> 31.8 ns 31.8 ns 22157591
BM_StdSqrt<std::complex<double>> 128 ns 128 ns 5437375
BM_Rsqrt<std::complex<float>> 31.9 ns 31.8 ns 22384383
BM_DivSqrt<std::complex<float>> 99.2 ns 98.9 ns 7250438
BM_Rsqrt<std::complex<double>> 46.0 ns 45.8 ns 15338689
BM_DivSqrt<std::complex<double>> 119 ns 119 ns 5898944
```
2021-01-17 08:50:57 -08:00
