[coll] Broadcast. (#9659)

src/common/bitfield.h

@@ -5,22 +5,21 @@
 #ifndef XGBOOST_COMMON_BITFIELD_H_
 #define XGBOOST_COMMON_BITFIELD_H_
 
-#include <algorithm>
-#include <bitset>
-#include <cinttypes>
-#include <iostream>
-#include <sstream>
-#include <string>
-#include <vector>
+#include <algorithm>    // for min
+#include <bitset>       // for bitset
+#include <cstdint>      // for uint32_t, uint64_t, uint8_t
+#include <ostream>      // for ostream
+#include <type_traits>  // for conditional_t, is_signed_v
 
 #if defined(__CUDACC__)
 #include <thrust/copy.h>
 #include <thrust/device_ptr.h>
+
 #include "device_helpers.cuh"
 #endif  // defined(__CUDACC__)
 
-#include "xgboost/span.h"
 #include "common.h"
+#include "xgboost/span.h"  // for Span
 
 namespace xgboost {
 
@@ -75,7 +74,7 @@ struct BitFieldContainer {
  private:
   value_type* bits_{nullptr};
   size_type n_values_{0};
-  static_assert(!std::is_signed<VT>::value, "Must use an unsiged type as the underlying storage.");
+  static_assert(!std::is_signed_v<VT>, "Must use an unsiged type as the underlying storage.");
 
  public:
   XGBOOST_DEVICE static Pos ToBitPos(index_type pos) {
@@ -240,11 +239,39 @@ struct RBitsPolicy : public BitFieldContainer<VT, RBitsPolicy<VT>> {
 
 // Format: <Const><Direction>BitField<size of underlying type in bits>, underlying type
 // must be unsigned.
-using LBitField64 = BitFieldContainer<uint64_t, LBitsPolicy<uint64_t>>;
-using RBitField8 = BitFieldContainer<uint8_t, RBitsPolicy<unsigned char>>;
+using LBitField64 = BitFieldContainer<std::uint64_t, LBitsPolicy<std::uint64_t>>;
+using RBitField8 = BitFieldContainer<std::uint8_t, RBitsPolicy<unsigned char>>;
 
-using LBitField32 = BitFieldContainer<uint32_t, LBitsPolicy<uint32_t>>;
-using CLBitField32 = BitFieldContainer<uint32_t, LBitsPolicy<uint32_t, true>, true>;
+using LBitField32 = BitFieldContainer<std::uint32_t, LBitsPolicy<std::uint32_t>>;
+using CLBitField32 = BitFieldContainer<std::uint32_t, LBitsPolicy<std::uint32_t, true>, true>;
+using RBitField32 = BitFieldContainer<std::uint32_t, RBitsPolicy<std::uint32_t>>;
+
+namespace detail {
+inline std::uint32_t TrailingZeroBitsImpl(std::uint32_t value) {
+  auto n = sizeof(value) * 8;
+  std::uint32_t cnt{0};
+  for (decltype(n) i = 0; i < n; i++) {
+    if ((value >> i) & 1) {
+      break;
+    }
+    cnt++;
+  }
+  return cnt;
+}
+}  // namespace detail
+
+inline std::uint32_t TrailingZeroBits(std::uint32_t value) {
+  if (value == 0) {
+    return sizeof(value) * 8;
+  }
+#if defined(__GNUC__)
+  return __builtin_ctz(value);
+#elif defined(_MSC_VER)
+  return _tzcnt_u32(value);
+#else
+  return detail::TrailingZeroBitsImpl(value);
+#endif  //  __GNUC__
+}
 }       // namespace xgboost
 
 #endif  // XGBOOST_COMMON_BITFIELD_H_

src/common/common.h

@@ -6,7 +6,6 @@
 #ifndef XGBOOST_COMMON_COMMON_H_
 #define XGBOOST_COMMON_COMMON_H_
 
-#include <algorithm>  // for max
 #include <array>      // for array
 #include <cmath>      // for ceil
 #include <cstddef>    // for size_t
@@ -181,7 +180,7 @@ inline void SetDevice(std::int32_t device) {
 #endif
 
 /**
- * Last index of a group in a CSR style of index pointer.
+ * @brief Last index of a group in a CSR style of index pointer.
  */
 template <typename Indexable>
 XGBOOST_DEVICE size_t LastOf(size_t group, Indexable const &indptr) {