add bitmap .

src/utils/bitmap.h

@@ -0,0 +1,45 @@
+#ifndef XGBOOST_UTILS_BITMAP_H_
+#define XGBOOST_UTILS_BITMAP_H_
+/*!
+ * \file bitmap.h
+ * \brief a simple implement of bitmap
+ * \author Tianqi Chen
+ */
+#include <vector>
+#include "./utils.h"
+
+namespace xgboost {
+namespace utils {
+/*! \brief bit map that contains set of bit indicators */
+struct BitMap {
+  /*! \brief internal data structure */
+  std::vector<uint32_t> data;
+  /*! 
+   * \brief resize the bitmap to be certain size 
+   * \param size the size of bitmap
+   */
+  inline void Resize(size_t size) {
+    data.resize((size + 31U) >> 5, 0);
+  }
+  /*! 
+   * \brief query the i-th position of bitmap 
+   * \param i the position in 
+   */
+  inline bool Get(size_t i) const {
+    return (data[i >> 5] >> (i & 31U)) & 1U;
+  }
+  /*! 
+   * \brief set i-th position to true 
+   * \param i position index
+   */
+  inline void SetTrue(size_t i) {
+    data[i >> 5] |= (1 << (i & 31U));
+  }
+  /*! \brief clear the bitmap, set all places to false */
+  inline void Clear(void) {
+    std::fill(data.begin(), data.end(), 0U);
+  }
+};
+}  // namespace utils
+}  // namespace xgboost
+#endif