Update GPU backend (#29)

* Update GPU memory management
* Add allocate_memory and free_memory

include/trigdx/gpu.hpp

@@ -11,7 +11,8 @@ public:
   GPUBackend();
   ~GPUBackend() override;
 
-  void init(size_t n = 0) override;
+  void *allocate_memory(size_t bytes) const override;
+  void free_memory(void *ptr) const override;
   void compute_sinf(size_t n, const float *x, float *s) const override;
   void compute_cosf(size_t n, const float *x, float *c) const override;
   void compute_sincosf(size_t n, const float *x, float *s,

include/trigdx/interface.hpp

@@ -1,6 +1,8 @@
 #pragma once
 
 #include <cstddef>
+#include <cstdint>
+#include <cstdlib>
 
 // Base interface for all math backends
 class Backend {
@@ -10,6 +12,12 @@ public:
   // Optional initialization
   virtual void init(size_t n = 0) {}
 
+  virtual void *allocate_memory(size_t bytes) const {
+    return static_cast<void *>(new uint8_t[bytes]);
+  };
+
+  virtual void free_memory(void *ptr) const { std::free(ptr); };
+
   // Compute sine for n elements
   virtual void compute_sinf(size_t n, const float *x, float *s) const = 0;