Cudf support. (#4745)

* Initial support for cudf integration.

* Add two C APIs for consuming data and metainfo.

* Add CopyFrom for SimpleCSRSource as a generic function to consume the data.

* Add FromDeviceColumnar for consuming device data.

* Add new MetaInfo::SetInfo for consuming label, weight etc.

tests/cpp/common/test_bitfield.cc

@@ -0,0 +1,92 @@
+/*!
+ * Copyright 2019 XGBoost contributors
+ */
+#include <gtest/gtest.h>
+#include "../../../src/common/bitfield.h"
+
+namespace xgboost {
+
+TEST(BitField, Check) {
+  {
+    std::vector<LBitField64::value_type> storage(4, 0);
+    storage[2] = 2;
+    auto bits = LBitField64({storage.data(),
+                static_cast<typename common::Span<LBitField64::value_type>::index_type>(
+                    storage.size())});
+    size_t true_bit = 190;
+    for (size_t i = true_bit + 1; i < bits.Size(); ++i) {
+      ASSERT_FALSE(bits.Check(i));
+    }
+    ASSERT_TRUE(bits.Check(true_bit));
+    for (size_t i = 0; i < true_bit; ++i) {
+      ASSERT_FALSE(bits.Check(i));
+    }
+  }
+
+  {
+    std::vector<RBitField8::value_type> storage(4, 0);
+    storage[2] = 1 << 3;
+    auto bits = RBitField8({storage.data(),
+                static_cast<typename common::Span<RBitField8::value_type>::index_type>(
+                    storage.size())});
+    size_t true_bit = 19;
+    for (size_t i = 0; i < true_bit; ++i) {
+      ASSERT_FALSE(bits.Check(i));
+    }
+    ASSERT_TRUE(bits.Check(true_bit));
+    for (size_t i = true_bit + 1; i < bits.Size(); ++i) {
+      ASSERT_FALSE(bits.Check(i));
+    }
+  }
+}
+
+template <typename BitFieldT, typename VT = typename BitFieldT::value_type>
+void TestBitFieldSet(typename BitFieldT::value_type res, size_t index, size_t true_bit) {
+  using IndexT = typename common::Span<VT>::index_type;
+  std::vector<VT> storage(4, 0);
+  auto bits = BitFieldT({storage.data(), static_cast<IndexT>(storage.size())});
+
+  bits.Set(true_bit);
+
+  for (size_t i = 0; i < true_bit; ++i) {
+    ASSERT_FALSE(bits.Check(i));
+  }
+
+  ASSERT_TRUE(bits.Check(true_bit));
+
+  for (size_t i = true_bit + 1; i < storage.size() * BitFieldT::kValueSize; ++i) {
+    ASSERT_FALSE(bits.Check(i));
+  }
+  ASSERT_EQ(storage[index], res);
+}
+
+TEST(BitField, Set) {
+  {
+    TestBitFieldSet<LBitField64>(2, 2, 190);
+  }
+  {
+    TestBitFieldSet<RBitField8>(1 << 3, 2, 19);
+  }
+}
+
+template <typename BitFieldT, typename VT = typename BitFieldT::value_type>
+void TestBitFieldClear(size_t clear_bit) {
+  using IndexT = typename common::Span<VT>::index_type;
+  std::vector<VT> storage(4, 0);
+  auto bits = BitFieldT({storage.data(), static_cast<IndexT>(storage.size())});
+
+  bits.Set(clear_bit);
+  bits.Clear(clear_bit);
+
+  ASSERT_FALSE(bits.Check(clear_bit));
+}
+
+TEST(BitField, Clear) {
+  {
+    TestBitFieldClear<LBitField64>(190);
+  }
+  {
+    TestBitFieldClear<RBitField8>(19);
+  }
+}
+}  // namespace xgboost