more work on backends

src/decoder/backend_gpu.h

@@ -0,0 +1,54 @@
+#pragma once
+
+#include "matrix.h"
+
+class BackendGPU /* : public Backend */ {
+  public:
+    template <typename T> 
+    using DeviceVector = thrust::device_vector<T>;
+    
+    template <typename T> 
+    using HostVector = thrust::host_vector<T>;
+    
+    class Payload : public PayloadBase {
+      public:
+        Payload() {}
+        
+        mblas::Matrix& operator*() {
+          return matrix_;
+        }
+        
+      private:    
+        mblas::Matrix matrix_;
+    };
+    
+    
+    static void PartialSortByKey(Payload& probs,
+                            HostVector<unsigned>& bestKeys,
+                            HostVector<float>& bestCosts) {
+      size_t beamSize = bestKeys.size();
+      if(beamSize < 10) {
+        for(size_t i = 0; i < beamSize; ++i) {
+          DeviceVector<float>::iterator iter =
+            thrust::max_element((*probs).begin(), (*probs).end());
+          bestKeys[i] = iter - (*probs).begin();
+          bestCosts[i] = *iter;
+          *iter = std::numeric_limits<float>::lowest();
+        }
+      }
+      else {
+        DeviceVector<unsigned> keys((*probs).size());
+        thrust::sequence(keys.begin(), keys.end());
+        thrust::sort_by_key((*probs).begin(), (*probs).end(),
+                            keys.begin(), thrust::greater<float>());
+      
+        thrust::copy_n(keys.begin(), beamSize, bestKeys.begin());
+        thrust::copy_n((*probs).begin(), beamSize, bestCosts.begin());
+      }
+    }
+    
+    template <class It1, class It2>
+    static void copy(It1 begin, It1 end, It2 out) {
+      thrust::copy(begin, end, out);
+    }
+};

src/decoder/sentence.cpp

@@ -0,0 +1,17 @@
+#include "sentence.h"
+#include "god.h"
+
+Sentence::Sentence(size_t lineNo, const std::string& line)
+: lineNo_(lineNo), line_(line)
+{
+  words_.push_back(God::GetSourceVocab(0)(line));
+}
+
+const Words& Sentence::GetWords(size_t index) const {
+  return words_[index];
+}
+
+size_t Sentence::GetLine() const {
+  return lineNo_;
+}
+