Add shallow hash function and shallow equality comparison for column_view

cpp/include/cudf/column/column_view.hpp

@@ -633,4 +633,45 @@ column_view bit_cast(column_view const& input, data_type type);
  */
 mutable_column_view bit_cast(mutable_column_view const& input, data_type type);
 
+namespace detail {
+/**
+ * @brief Computes a hash value from the shallow state of the specified column
+ *
+ * For any two columns, if `is_shallow_equivalent(c0,c1)` then `shallow_hash(c0) ==
+ * shallow_hash(c1)`.
+ *
+ * The complexity of computing the hash value of `input` is `O( count_descendants(input) )`, i.e.,
+ * it is independent of the number of elements in the column.
+ *
+ * This function does _not_ inspect the elements of `input` nor access any device memory or launch
+ * any kernels.
+ *
+ * @param input The `column_view` to compute hash
+ * @return The hash value derived from the shallow state of `input`.
+ */
+std::size_t shallow_hash(column_view const& input);
+
+/**
+ * @brief Uses only shallow state to determine if two `column_view`s view equivalent columns
+ *
+ *  Two columns are equivalent if for any operation `F` then:
+ *   ```
+ *    is_shallow_equivalent(c0, c1) ==> The results of F(c0) and F(c1) are equivalent
+ *   ```
+ * For any two non-empty columns, `is_shallow_equivalent(c0,c1)` is true only if they view the exact
+ * same physical column. In other words, two physically independent columns may have exactly
+ * equivalent elements but their shallow state would not be equivalent.
+ *
+ * The complexity of this function is `O( min(count_descendants(lhs), count_descendants(rhs)) )`,
+ * i.e., it is independent of the number of elements in either column.
+ *
+ * This function does _not_ inspect the elements of `lhs` or `rhs` nor access any device memory nor
+ * launch any kernels.
+ *
+ * @param lhs The left `column_view` to compare
+ * @param rhs The right `column_view` to compare
+ * @return If `lhs` and `rhs` have equivalent shallow state
+ */
+bool is_shallow_equivalent(column_view const& lhs, column_view const& rhs);
+}  // namespace detail
 }  // namespace cudf

cpp/include/cudf/detail/hashing.hpp

@@ -19,6 +19,9 @@
 
 #include <rmm/cuda_stream_view.hpp>
 
+#include <cstddef>
+#include <functional>
+
 namespace cudf {
 namespace detail {
 
@@ -53,5 +56,38 @@ std::unique_ptr<column> serial_murmur_hash3_32(
   rmm::cuda_stream_view stream        = rmm::cuda_stream_default,
   rmm::mr::device_memory_resource* mr = rmm::mr::get_current_device_resource());
 
+/* Copyright 2005-2014 Daniel James.
+ *
+ * Use, modification and distribution is subject to the Boost Software
+ * License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+ * http://www.boost.org/LICENSE_1_0.txt)
+ */
+/**
+ * @brief Combines two hashed values into a single hashed value.
+ *
+ * Adapted from Boost hash_combine function, modified for 64-bit
+ * https://www.boost.org/doc/libs/1_35_0/doc/html/boost/hash_combine_id241013.html
+ *
+ * @param lhs The first hashed value
+ * @param rhs The second hashed value
+ * @return Combined hash value
+ */
+constexpr std::size_t hash_combine(std::size_t lhs, std::size_t rhs)
+{
+  lhs ^= rhs + 0x9e3779b97f4a7c15 + (lhs << 6) + (lhs >> 2);
+  return lhs;
+}
 }  // namespace detail
 }  // namespace cudf
+
+// specialization of std::hash for cudf::data_type
+namespace std {
+template <>
+struct hash<cudf::data_type> {
+  std::size_t operator()(cudf::data_type const& type) const noexcept
+  {
+    return cudf::detail::hash_combine(std::hash<int32_t>{}(static_cast<int32_t>(type.id())),
+                                      std::hash<int32_t>{}(type.scale()));
+  }
+};
+}  // namespace std

cpp/include/cudf/detail/utilities/hash_functions.cuh

@@ -395,6 +395,12 @@ struct MurmurHash3_32 {
     return h;
   }
 
+  /* Copyright 2005-2014 Daniel James.
+   *
+   * Use, modification and distribution is subject to the Boost Software
+   * License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+   * http://www.boost.org/LICENSE_1_0.txt)
+   */
   /**
    * @brief  Combines two hash values into a new single hash value. Called
    * repeatedly to create a hash value from several variables.
@@ -795,6 +801,12 @@ struct IdentityHash {
   IdentityHash()    = default;
   constexpr IdentityHash(uint32_t seed) : m_seed(seed) {}
 
+  /* Copyright 2005-2014 Daniel James.
+   *
+   * Use, modification and distribution is subject to the Boost Software
+   * License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+   * http://www.boost.org/LICENSE_1_0.txt)
+   */
   /**
    * @brief  Combines two hash values into a new single hash value. Called
    * repeatedly to create a hash value from several variables.

cpp/include/cudf_test/type_lists.hpp

@@ -315,6 +315,18 @@ using FixedWidthTypesWithoutChrono = Concat<NumericTypes, FixedPointTypes>;
  */
 using ComparableTypes = Concat<NumericTypes, ChronoTypes, StringTypes>;
 
+/**
+ * @brief Provides a list of all compound types for use in GTest typed tests.
+ *
+ * Example:
+ * ```
+ * // Invokes all typed fixture tests for all compound types in libcudf
+ * TYPED_TEST_CASE(MyTypedFixture, cudf::test::CompoundTypes);
+ * ```
+ */
+using CompoundTypes =
+  cudf::test::Types<cudf::string_view, cudf::dictionary32, cudf::list_view, cudf::struct_view>;
+
 /**
  * @brief Provides a list of all types supported in libcudf for use in a GTest
  * typed test.

cpp/src/column/column_view.cpp

@@ -15,13 +15,15 @@
  */
 
 #include <cudf/column/column_view.hpp>
+#include <cudf/detail/hashing.hpp>
 #include <cudf/null_mask.hpp>
 #include <cudf/types.hpp>
 #include <cudf/utilities/error.hpp>
 #include <cudf/utilities/traits.hpp>
 
 #include <thrust/iterator/transform_iterator.h>
 
+#include <algorithm>
 #include <exception>
 #include <numeric>
 #include <vector>
@@ -76,6 +78,59 @@ size_type column_view_base::null_count(size_type begin, size_type end) const
            ? 0
            : cudf::count_unset_bits(null_mask(), offset() + begin, offset() + end);
 }
+
+// Struct to use custom hash combine and fold expression
+struct HashValue {
+  std::size_t hash;
+  explicit HashValue(std::size_t h) : hash{h} {}
+  HashValue operator^(HashValue const& other) const
+  {
+    return HashValue{hash_combine(hash, other.hash)};
+  }
+};
+
+template <typename... Ts>
+constexpr auto hash(Ts&&... ts)
+{
+  return (... ^ HashValue(std::hash<Ts>{}(ts))).hash;
+}
+
+std::size_t shallow_hash_impl(column_view const& c, bool is_parent_empty = false)
+{
+  std::size_t const init = (c.is_empty() or is_parent_empty)
+                             ? hash(c.type(), c.size())
+                             : hash(c.type(), c.size(), c.head(), c.null_mask(), c.offset());
+  return std::accumulate(c.child_begin(),
+                         c.child_end(),
+                         init,
+                         [&c, is_parent_empty](std::size_t hash, auto const& child) {
+                           return hash_combine(
+                             hash, shallow_hash_impl(child, c.is_empty() or is_parent_empty));
+                         });
+}
+
+std::size_t shallow_hash(column_view const& input) { return shallow_hash_impl(input); }
+
+bool shallow_equal_impl(column_view const& lhs,
+                        column_view const& rhs,
+                        bool is_parent_empty = false)
+{
+  bool const is_empty = (lhs.is_empty() and rhs.is_empty()) or is_parent_empty;
+  return (lhs.type() == rhs.type()) and
+         (is_empty or ((lhs.size() == rhs.size()) and (lhs.head() == rhs.head()) and
+                       (lhs.null_mask() == rhs.null_mask()) and (lhs.offset() == rhs.offset()))) and
+         std::equal(lhs.child_begin(),
+                    lhs.child_end(),
+                    rhs.child_begin(),
+                    rhs.child_end(),
+                    [is_empty](auto const& lhs_child, auto const& rhs_child) {
+                      return shallow_equal_impl(lhs_child, rhs_child, is_empty);
+                    });
+}
+bool is_shallow_equivalent(column_view const& lhs, column_view const& rhs)
+{
+  return shallow_equal_impl(lhs, rhs);
+}
 }  // namespace detail
 
 // Immutable view constructor

cpp/tests/CMakeLists.txt

@@ -33,6 +33,7 @@ endfunction()
 # - column tests ----------------------------------------------------------------------------------
 ConfigureTest(COLUMN_TEST
     column/bit_cast_test.cpp
+    column/column_view_shallow_test.cpp
     column/column_test.cu
     column/column_device_view_test.cu
     column/compound_test.cu)