Use Pimpl idiom for LookupBackend

src/CMakeLists.txt

@@ -1,4 +1,4 @@
-add_library(trigdx reference.cpp)
+add_library(trigdx reference.cpp lookup.cpp)
 
 target_include_directories(trigdx PUBLIC ${PROJECT_SOURCE_DIR}/include)
 

src/lookup.cpp

@@ -0,0 +1,72 @@
+#include <cmath>
+#include <memory>
+#include <vector>
+
+#include "trigdx/lookup.hpp"
+
+template <size_t NR_SAMPLES> struct LookupBackend<NR_SAMPLES>::Impl {
+  std::vector<float> lookup;
+  static constexpr size_t MASK = NR_SAMPLES - 1;
+  static constexpr float SCALE = NR_SAMPLES / (2.0f * float(M_PI));
+
+  void init() {
+    lookup.resize(NR_SAMPLES);
+    for (size_t i = 0; i < NR_SAMPLES; ++i)
+      lookup[i] = std::sinf(i * (2.0f * float(M_PI) / NR_SAMPLES));
+  }
+
+  void compute_sinf(size_t n, const float *x, float *s) const {
+    for (size_t i = 0; i < n; ++i) {
+      size_t idx = static_cast<size_t>(x[i] * SCALE) & MASK;
+      s[i] = lookup[idx];
+    }
+  }
+
+  void compute_cosf(size_t n, const float *x, float *c) const {
+    for (size_t i = 0; i < n; ++i) {
+      size_t idx = static_cast<size_t>(x[i] * SCALE) & MASK;
+      size_t idx_cos = (idx + NR_SAMPLES / 4) & MASK;
+      c[i] = lookup[idx_cos];
+    }
+  }
+
+  void compute_sincosf(size_t n, const float *x, float *s, float *c) const {
+    for (size_t i = 0; i < n; ++i) {
+      size_t idx = static_cast<size_t>(x[i] * SCALE) & MASK;
+      size_t idx_cos = (idx + NR_SAMPLES / 4) & MASK;
+      s[i] = lookup[idx];
+      c[i] = lookup[idx_cos];
+    }
+  }
+};
+
+template <size_t NR_SAMPLES>
+LookupBackend<NR_SAMPLES>::LookupBackend() : impl(std::make_unique<Impl>()) {}
+
+template <size_t NR_SAMPLES>
+LookupBackend<NR_SAMPLES>::~LookupBackend() = default;
+
+template <size_t NR_SAMPLES> void LookupBackend<NR_SAMPLES>::init() {
+  impl->init();
+}
+
+template <size_t NR_SAMPLES>
+void LookupBackend<NR_SAMPLES>::compute_sinf(size_t n, const float *x,
+                                             float *s) const {
+  impl->compute_sinf(n, x, s);
+}
+
+template <size_t NR_SAMPLES>
+void LookupBackend<NR_SAMPLES>::compute_cosf(size_t n, const float *x,
+                                             float *c) const {
+  impl->compute_cosf(n, x, c);
+}
+
+template <size_t NR_SAMPLES>
+void LookupBackend<NR_SAMPLES>::compute_sincosf(size_t n, const float *x,
+                                                float *s, float *c) const {
+  impl->compute_sincosf(n, x, s, c);
+}
+
+template class LookupBackend<16384>;
+template class LookupBackend<32768>;