/*!
 * Copyright 2020-2021 by XGBoost Contributors
 */
#ifndef HISTOGRAM_CUH_
#define HISTOGRAM_CUH_
#include <thrust/transform.h>

#include "feature_groups.cuh"

#include "../../data/ellpack_page.cuh"

namespace xgboost {
namespace tree {

template <typename GradientSumT>
GradientSumT CreateRoundingFactor(common::Span<GradientPair const> gpair);

template <typename T, typename U>
XGBOOST_DEV_INLINE T TruncateWithRoundingFactor(T const rounding_factor, U const x) {
  static_assert(sizeof(T) >= sizeof(U), "Rounding must have higher or equal precision.");
  return (rounding_factor + static_cast<T>(x)) - rounding_factor;
}

template <typename GradientSumT>
void BuildGradientHistogram(EllpackDeviceAccessor const& matrix,
                            FeatureGroupsAccessor const& feature_groups,
                            common::Span<GradientPair const> gpair,
                            common::Span<const uint32_t> ridx,
                            common::Span<GradientSumT> histogram,
                            GradientSumT rounding);
}  // namespace tree
}  // namespace xgboost

#endif  // HISTOGRAM_CUH_