use openmp in PixelHistogram

- updated custom targets clang-format, check-format, clang-tidy
- find: paths must precede expression: `\' (double \\ not properly
escaped in bash)

benchmarks/HistogramBenchmark.cpp

@@ -0,0 +1,83 @@
+#include "aare/hist/PixelHistogram.hpp"
+#include "aare/hist/PixelHistogramOpenMP.hpp"
+#include <benchmark/benchmark.h>
+#include <random>
+
+using namespace aare;
+
+class TestHistogram : public benchmark::Fixture {
+  public:
+    std::vector<NDArray<float, 2>> images;
+    void SetUp(::benchmark::State &state) {
+
+        std::cout << "In Fixture Setup" << std::endl;
+
+        std::mt19937 gen(rd()); // to seed mersenne twister.
+        std::uniform_real_distribution<float> dist(xmin, xmax);
+
+        images.resize(num_images);
+
+        //
+
+        for (size_t i = 0; i < num_images; ++i) {
+            NDArray<float, 2> image({rows, cols});
+            for (ssize_t r = 0; r < rows; ++r) {
+                for (ssize_t c = 0; c < cols; ++c) {
+                    image(r, c) = dist(gen);
+                }
+            }
+            images[i] = std::move(image);
+        }
+    }
+
+    // void TearDown(::benchmark::State& state) {
+    // }
+
+    const ssize_t rows = 512;
+    const ssize_t cols = 1024;
+    const size_t n_bins = 200;
+    const float xmin = 600.0f;
+    const float xmax = 1400.0f;
+    const size_t num_images = 1000;
+
+  private:
+    std::random_device rd{};
+};
+
+BENCHMARK_DEFINE_F(TestHistogram, process_histogram_openmp)
+(benchmark::State &st) {
+    const int num_threads = st.range(0);
+
+    PixelHistogramOpenMP hist(rows, cols, n_bins, xmin, xmax, num_threads);
+    for (auto _ : st) {
+        // This code gets timed
+        for (const auto &img : images) {
+            hist.fill_async(NDArray<float, 2>(img));
+        }
+        auto result = hist.values();
+        benchmark::DoNotOptimize(result);
+    }
+}
+
+BENCHMARK_DEFINE_F(TestHistogram, process_histogram)(benchmark::State &st) {
+    const int num_threads = st.range(0);
+    PixelHistogram hist(rows, cols, n_bins, xmin, xmax, num_threads);
+    for (auto _ : st) {
+        // This code gets timed
+        for (const auto &img : images) {
+            hist.fill_async(NDArray<float, 2>(img));
+        }
+        auto result = hist.values();
+        benchmark::DoNotOptimize(result);
+    }
+}
+
+BENCHMARK_REGISTER_F(TestHistogram, process_histogram)
+    ->DenseRange(1, 20)
+    ->Iterations(10); // 1 to 20 threads
+
+BENCHMARK_REGISTER_F(TestHistogram, process_histogram_openmp)
+    ->DenseRange(1, 20)
+    ->Iterations(10); // 1 to 20 threads
+
+// BENCHMARK_MAIN();