From 066d9d85d2e315235312296580f3c9ad64d404eb Mon Sep 17 00:00:00 2001
From: Andreas Tsouchlos <an.tsouchlos@gmail.com>
Date: Fri, 25 Nov 2022 14:00:19 +0100
Subject: [PATCH] Finished cpp proximal decoder implementation

---
 .gitignore                  |  2 ++
 sw/cpp/CMakeLists.txt       | 21 ++++++++++++--
 sw/cpp/src/cpp_decoders.cpp | 58 ++++++++-----------------------------
 3 files changed, 33 insertions(+), 48 deletions(-)

diff --git a/.gitignore b/.gitignore
index 987729f..29c1db1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,6 +2,8 @@ latex/build/
 latex/tmp/
 sw/cpp_modules
 sw/cpp/build
+sw/cpp/cmake-build-debug
+sw/cpp/cmake-build-release
 sw/sim_saves/
 .idea
 __pycache__
diff --git a/sw/cpp/CMakeLists.txt b/sw/cpp/CMakeLists.txt
index 95869fc..f1ef167 100644
--- a/sw/cpp/CMakeLists.txt
+++ b/sw/cpp/CMakeLists.txt
@@ -1,14 +1,31 @@
 cmake_minimum_required (VERSION 3.0)
 project(cpp_decoders)
- 
+
+
+if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
+    message(STATUS "Setting build type to 'Release' as none was specified.")
+    set(CMAKE_BUILD_TYPE
+            Release
+            CACHE STRING "Choose the type of build." FORCE)
+    set_property(
+            CACHE CMAKE_BUILD_TYPE
+            PROPERTY STRINGS
+            "Debug"
+            "Release")
+endif()
+
+set(CMAKE_CXX_STANDARD 23)
+
 find_package(Eigen3 3.3 REQUIRED NO_MODULE)
 find_package(pybind11 CONFIG REQUIRED)
 
 include_directories(${pybind11_INCLUDE_DIRS})
 
 
+find_package(OpenMP REQUIRED)
+
 pybind11_add_module(cpp_decoders src/cpp_decoders.cpp)
-target_link_libraries(cpp_decoders PRIVATE Eigen3::Eigen)
+target_link_libraries(cpp_decoders PRIVATE Eigen3::Eigen OpenMP::OpenMP_CXX)
 
 set(INSTALL_DIR ${CMAKE_CURRENT_SOURCE_DIR}/../cpp_modules)
 
diff --git a/sw/cpp/src/cpp_decoders.cpp b/sw/cpp/src/cpp_decoders.cpp
index e7f102e..bb519bf 100644
--- a/sw/cpp/src/cpp_decoders.cpp
+++ b/sw/cpp/src/cpp_decoders.cpp
@@ -1,53 +1,14 @@
-#include <Eigen/Cholesky>
+#include <Eigen/Dense>
 #include <iostream>
+
 #include <pybind11/numpy.h>
 #include <pybind11/pybind11.h>
 #include <pybind11/stl.h>
 
 #include <pybind11/eigen.h>
 
+#include <bit>
 
-/*
-
- import numpy as np
-
-
-class ProximalDecoder:
-    """Class implementing the Proximal Decoding algorithm. See "Proximal
-    Decoding for LDPC Codes"
-    by Tadashi Wadayama, and Satoshi Takabe.
-    """
-
-    def decode(self, y: np.array) -> np.array:
-        """Decode a received signal. The algorithm is detailed in 3.2, p.3.
-
-        This function assumes a BPSK modulated signal and an AWGN channel.
-
-        :param y: Vector of received values. (y = x + w, where 'x' is
-        element of [-1, 1]^n and 'w' is noise)
-        :return: Most probably sent codeword (element of [0, 1]^n). If
-        decoding fails, the returned value is 'None'
-        """
-        s = np.zeros(self._n)
-        x_hat = np.zeros(self._n)
-        for k in range(self._K):
-            r = s - self._step_size * self._L_awgn(s, y)
-
-            s = r - self._gamma * self._grad_h(r)
-            s = self._projection(s)  # Equation (15)
-
-            x_hat = np.sign(s)
-
-            # Map the codeword from [ -1, 1]^n to [0, 1]^n
-            x_hat = (x_hat == -1) * 1
-
-            if self._check_parity(x_hat):
-                return x_hat
-
-        return None
-
-
- * */
 
 namespace py11 = pybind11;
 using namespace pybind11::literals;
@@ -66,6 +27,8 @@ public:
                     double gamma, double eta)
         : mN(H.cols()), mK(K), mOmega(omega), mGamma(gamma), mEta(eta), mH(H),
           mH_zero_indices(find_zero(H)) {
+
+        Eigen::setNbThreads(8);
     }
 
     const std::optional<Eigen::RowVectorXi>
@@ -76,10 +39,14 @@ public:
 
         for (std::size_t i = 0; i < mK; ++i) {
             r = s - mOmega * L_awgn(s, y);
+
             s = projection(r - mGamma * grad_H(r));
 
-            x_hat = s.cast<int>().cwiseSign();
-            x_hat = (x_hat.array() - 1).matrix() / (-2);
+            x_hat = s.unaryExpr([](double d) {
+                         uint64_t bits = std::bit_cast<uint64_t>(d);
+                         // Return the sign bit: 1 for negative, 0 for positive
+                         return (bits >> 63);
+                     }).cast<int>();
 
             if (check_parity(x_hat)) {
                 return x_hat;
@@ -96,8 +63,7 @@ private:
     const double mGamma;
     const double mEta;
 
-    const MatrixXiR mH;
-
+    const MatrixXiR                 mH;
     const std::vector<Eigen::Index> mH_zero_indices;