From d847d3fdcf3fafd7e2c69ea1dc4dd6c20e42a823 Mon Sep 17 00:00:00 2001
From: Carles Fernandez <carles.fernandez@gmail.com>
Date: Thu, 11 Jun 2020 12:09:55 +0200
Subject: [PATCH] Add test about preamble correlation implementations

---
 src/tests/test_main.cc                        |   1 +
 .../arithmetic/preamble_correlator_test.cc    | 107 ++++++++++++++++++
 2 files changed, 108 insertions(+)
 create mode 100644 src/tests/unit-tests/arithmetic/preamble_correlator_test.cc

diff --git a/src/tests/test_main.cc b/src/tests/test_main.cc
index 3d54ce6bd..00639b3db 100644
--- a/src/tests/test_main.cc
+++ b/src/tests/test_main.cc
@@ -49,6 +49,7 @@ DECLARE_string(log_dir);
 #include "unit-tests/arithmetic/fft_speed_test.cc"
 #include "unit-tests/arithmetic/magnitude_squared_test.cc"
 #include "unit-tests/arithmetic/multiply_test.cc"
+#include "unit-tests/arithmetic/preamble_correlator_test.cc"
 #include "unit-tests/control-plane/control_thread_test.cc"
 #include "unit-tests/control-plane/file_configuration_test.cc"
 #include "unit-tests/control-plane/gnss_block_factory_test.cc"
diff --git a/src/tests/unit-tests/arithmetic/preamble_correlator_test.cc b/src/tests/unit-tests/arithmetic/preamble_correlator_test.cc
new file mode 100644
index 000000000..76ca3d681
--- /dev/null
+++ b/src/tests/unit-tests/arithmetic/preamble_correlator_test.cc
@@ -0,0 +1,107 @@
+/*!
+ * \file preamble_correlator_test.cc
+ * \brief  This file implements tests for preamble detection.
+ * \author Carles Fernandez-Prades, 2020. cfernandez(at)cttc.es
+ *
+ *
+ * -------------------------------------------------------------------------
+ *
+ * Copyright (C) 2010-2019  (see AUTHORS file for a list of contributors)
+ *
+ * GNSS-SDR is a software defined Global Navigation
+ *          Satellite Systems receiver
+ *
+ * This file is part of GNSS-SDR.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * -------------------------------------------------------------------------
+ */
+
+#include "GPS_L1_CA.h"
+#include <array>
+#include <chrono>
+#include <cstdint>
+#include <numeric>
+#include <random>
+#include <vector>
+
+TEST(PreambleCorrelationTest, TestMethods)
+{
+    int64_t n_iter = 100000;
+    int32_t corr_value = 0;
+    int32_t corr_value2 = 0;
+
+    int32_t sum_corr1 = 0;
+    int32_t sum_corr2 = 0;
+
+    std::vector<float> d_symbol_history(GPS_CA_PREAMBLE_LENGTH_SYMBOLS, 0.0);
+    std::array<int32_t, GPS_CA_PREAMBLE_LENGTH_BITS> d_preamble_samples{};
+
+    std::chrono::time_point<std::chrono::system_clock> start, end, start2, end2;
+
+    // fill the inputs
+    std::random_device rd;
+    std::default_random_engine e2(rd());
+    std::uniform_real_distribution<> dist(-1.0, 1.0);
+    for (int32_t i = 0; i < GPS_CA_PREAMBLE_LENGTH_SYMBOLS; i++)
+        {
+            d_symbol_history[i] = dist(e2);
+        }
+
+    int32_t n = 0;
+    for (int32_t i = 0; i < GPS_CA_PREAMBLE_LENGTH_BITS; i++)
+        {
+            if (GPS_CA_PREAMBLE[i] == '1')
+                {
+                    d_preamble_samples[n] = 1;
+                    n++;
+                }
+            else
+                {
+                    d_preamble_samples[n] = -1;
+                    n++;
+                }
+        }
+
+    // Compute correlation, method 1
+    start = std::chrono::system_clock::now();
+    for (int64_t kk = 0; kk < n_iter; kk++)
+        {
+            corr_value = 0;
+            for (int32_t i = 0; i < GPS_CA_PREAMBLE_LENGTH_BITS; i++)
+                {
+                    if (d_symbol_history[i] < 0.0)
+                        {
+                            corr_value -= d_preamble_samples[i];
+                        }
+                    else
+                        {
+                            corr_value += d_preamble_samples[i];
+                        }
+                }
+            sum_corr1 += corr_value;
+        }
+    end = std::chrono::system_clock::now();
+
+    // Compute correlation, method 2
+    start2 = std::chrono::system_clock::now();
+    for (int64_t kk = 0; kk < n_iter; kk++)
+        {
+            int32_t ii = -1;
+            corr_value2 = std::accumulate(d_symbol_history.begin(),
+                d_symbol_history.begin() + GPS_CA_PREAMBLE_LENGTH_BITS,
+                0,
+                [&ii, &d_preamble_samples](float a, float b) { return (b > 0.0 ? a + d_preamble_samples[++ii] : a - d_preamble_samples[++ii]); });
+            sum_corr2 += corr_value2;
+        }
+    end2 = std::chrono::system_clock::now();
+
+    EXPECT_EQ(corr_value, corr_value2);
+    EXPECT_EQ(sum_corr1, sum_corr2);
+
+    std::chrono::duration<double> elapsed_seconds = end - start;
+    std::chrono::duration<double> elapsed_seconds2 = end2 - start2;
+    std::cout << "Correlation computed with 'C for': done in " << elapsed_seconds.count() * 1.0e9 / n_iter << " nanoseconds" << std::endl;
+    std::cout << "Correlation computed with lambda:  done in " << elapsed_seconds2.count() * 1.0e9 / n_iter << " nanoseconds" << std::endl;
+}