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Uladzimir KarpenkaandClaude Opus 4.8
9960a1d0e3
The tap loop wrapped the ring with a test on every tap:
if ((idx_out = idx_in + j) >= ringsize) idx_out -= ringsize;
which made the address non-affine and stopped the vectorizer. Split the
walk at the wrap point instead, so both halves are unit-stride, and split
the complex ring into separate I/Q arrays so the taps load contiguously
rather than through a de-interleaving ld2.
The dot product also could not be vectorized as written: reassociating an
fp reduction needs -ffast-math, which this library must not enable (it
relies on IEEE semantics for 0/0 = NaN and x/0 = Inf, see linux_port.h).
Carry four independent accumulator pairs instead, which both breaks the
FMA dependency chain and lets the vectorizer in on any compiler.
Measured on an Apple M1 Pro, 512-sample DSP buffers, best of 5:
xresample, decimation to 48 kHz before after speedup
192k -> 48k (561 taps) 342.0 us 84.2 us 4.06x
384k -> 48k (1121 taps) 708.9 us 175.1 us 4.05x
576k -> 48k (1681 taps) 1074.4 us 266.9 us 4.03x
768k -> 48k (2241 taps) 1438.9 us 360.0 us 4.00x
full xrxa() chain, 576k input 1148.2 us 337.6 us 3.40x
10.76% 3.16% of one core
xresampleF (float, host audio) 2.6x - 3.4x
Summation order changes, so the double path is not bit-identical: over
400 buffers of the full RX chain the worst deviation is 1.1e-12, an SNR
of 251 dB. The float path is bit-identical, as the cast to float absorbs
the difference. With the resampler bypassed (48k in, 48k out) the chain
is unchanged bit-for-bit.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
WDSP
DSP library for SDR (Software Defined Radio) applications.
Originally written for Windows by Warren Pratt, NR0V. Ported to Linux and Android by John Melton G0ORX/N6LYT.
Project structure
wdsp/
├── *.c / *.h — WDSP library sources
├── org_openhpsdr_dsp_Wdsp.c/.h — JNI bridge
├── Makefile — host build (Linux / macOS)
├── Makefile.android — Android cross-build
├── java/
│ └── org/openhpsdr/dsp/Wdsp.java
├── third_party/
│ ├── fftw/ — FFTW source (download manually, see below)
│ ├── rnnoise/ — RNNoise noise suppression
│ └── libspecbleach/ — spectral noise reduction
├── obj/ — object files (generated)
└── lib/ — built libraries (generated)
Host build (Linux / macOS)
Dependencies
Linux:
sudo apt install build-essential libfftw3-dev pkg-config default-jdk
macOS:
brew install fftw pkg-config
Build
# Full build: static + shared + JNI library + Java classes
make
# Individual targets
make static # lib/libwdsp.a
make shared # lib/libwdsp.so (or .dylib on macOS)
make java # lib/libwdspj.so + java/build/
Install
sudo make install # installs to /usr/local/lib and /usr/local/include
sudo make PREFIX=/opt/wdsp install # custom prefix
sudo make install_java # install libwdspj alongside libwdsp
Options
| Variable | Default | Description |
|---|---|---|
PREFIX |
/usr/local |
Install prefix |
NR34LIB |
off | Set to ON to skip bundled rnnoise/libspecbleach |
CC |
gcc |
C compiler |
CFLAGS |
-pthread -O3 ... |
Compiler flags |
make NR34LIB=ON # build without NR3/NR4 noise reduction
make CC=clang
Clean
make clean
Android build
Prerequisites
- Android NDK r23 or newer
- FFTW source — download and extract into
third_party/fftw/:
wget https://www.fftw.org/fftw-3.3.10.tar.gz
tar xf fftw-3.3.10.tar.gz
mv fftw-3.3.10 third_party/fftw
- Java compiler — for building the
.classfile (Android Studio's JBR or any JDK)
Build
make android
# or directly
make -f Makefile.android
Output is placed into:
lib/android/
├── arm64-v8a/
│ ├── libfftw3.so
│ ├── libfftw3f.so
│ ├── libwdsp.so
│ └── libwdspj.so
├── armeabi-v7a/
│ └── ...
├── x86_64/
│ └── ...
└── java/
└── org/openhpsdr/dsp/Wdsp.class
libwdsp.so has FFTW linked statically — no separate FFTW dependency at runtime on the device.
Options
| Variable | Default | Description |
|---|---|---|
ANDROID_NDK |
/home/vladimir/Android/Sdk/ndk/29.0.14206865 |
Path to Android NDK |
ANDROID_API |
24 |
Minimum API level |
ANDROID_ABIS |
arm64-v8a armeabi-v7a x86_64 |
Target ABIs |
ANDROID_HOST_TAG |
auto-detected | Host platform (linux-x86_64, darwin-x86_64, etc.) |
FFTW_SRC |
third_party/fftw |
Path to FFTW source |
JAVAC |
/opt/android-studio/jbr/bin/javac |
Java compiler |
make -f Makefile.android \
ANDROID_NDK=~/Android/Sdk/ndk/26.3.11579264 \
ANDROID_API=26 \
ANDROID_ABIS=arm64-v8a
Clean
make -f Makefile.android clean
# removes obj/android/ and lib/android/
Using in an Android project
Copy lib/android/{abi}/ into your Android project's jniLibs:
app/src/main/jniLibs/
├── arm64-v8a/
│ ├── libwdsp.so
│ └── libwdspj.so
├── armeabi-v7a/
│ └── ...
└── x86_64/
└── ...
Add Wdsp.java to your source tree and load the libraries at startup:
System.loadLibrary("wdsp");
System.loadLibrary("wdspj");
Or use the singleton:
Wdsp wdsp = Wdsp.getInstance();