js8544 commented on code in PR #35787:
URL: https://github.com/apache/arrow/pull/35787#discussion_r1246046104


##########
cpp/src/arrow/compute/kernels/vector_pairwise.cc:
##########
@@ -0,0 +1,182 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+// Vector kernels for pairwise computation
+
+#include <iostream>
+#include <memory>
+#include "arrow/builder.h"
+#include "arrow/compute/api_vector.h"
+#include "arrow/compute/exec.h"
+#include "arrow/compute/function.h"
+#include "arrow/compute/kernel.h"
+#include "arrow/compute/kernels/base_arithmetic_internal.h"
+#include "arrow/compute/kernels/codegen_internal.h"
+#include "arrow/compute/registry.h"
+#include "arrow/compute/util.h"
+#include "arrow/status.h"
+#include "arrow/type.h"
+#include "arrow/type_fwd.h"
+#include "arrow/type_traits.h"
+#include "arrow/util/bit_util.h"
+#include "arrow/util/checked_cast.h"
+#include "arrow/util/logging.h"
+#include "arrow/visit_type_inline.h"
+
+namespace arrow::compute::internal {
+
+// We reuse the kernel exec function of a scalar binary function to compute 
pairwise
+// results. For example, for pairwise_diff, we reuse subtract's kernel exec.
+struct PairwiseState : KernelState {
+  PairwiseState(const PairwiseOptions& options, const ArrayKernelExec& 
scalar_exec)
+      : periods(options.periods), scalar_exec(scalar_exec) {}
+
+  int64_t periods;
+  const ArrayKernelExec& scalar_exec;
+};
+
+KernelInit GeneratePairwiseInit(const ArrayKernelExec& scalar_exec) {
+  return [&scalar_exec](KernelContext* ctx, const KernelInitArgs& args) {
+    return std::make_unique<PairwiseState>(
+        checked_cast<const PairwiseOptions&>(*args.options), scalar_exec);
+  };
+}
+
+/// A generic pairwise implementation that can be reused by different ops.
+Status PairwiseExecImpl(KernelContext* ctx, const ArraySpan& input,
+                        const ArrayKernelExec& scalar_exec, int64_t periods,
+                        ArrayData* result) {
+  auto offset = abs(periods);
+  offset = std::min(offset, input.length);
+  auto exec_length = input.length - offset;
+  // prepare bitmap
+  auto null_start = periods > 0 ? 0 : exec_length;
+  auto non_null_start = periods > 0 ? offset : 0;
+  bit_util::ClearBitmap(result->buffers[0]->mutable_data(), null_start, 
offset);
+  for (int64_t i = non_null_start; i < non_null_start + exec_length; i++) {
+    if (input.IsValid(i) && input.IsValid(i - periods)) {
+      bit_util::SetBit(result->buffers[0]->mutable_data(), i);
+    } else {
+      bit_util::ClearBit(result->buffers[0]->mutable_data(), i);
+    }
+  }
+  // prepare input span
+  ArraySpan left(input);
+  left.SetSlice(periods > 0 ? offset : 0, exec_length);
+  ArraySpan right(input);
+  right.SetSlice(periods > 0 ? 0 : offset, exec_length);
+  // prepare output span
+  ArraySpan output_span;
+  output_span.SetMembers(*result);
+  output_span.offset = periods > 0 ? offset : 0;
+  output_span.length = exec_length;
+  ExecResult output{output_span};
+  // execute scalar function
+  RETURN_NOT_OK(scalar_exec(ctx, ExecSpan({left, right}, exec_length), 
&output));
+
+  return Status::OK();
+}
+
+Status PairwiseExec(KernelContext* ctx, const ExecSpan& batch, ExecResult* 
out) {
+  const auto& state = checked_cast<const PairwiseState&>(*ctx->state());
+  auto input = batch[0].array;
+  RETURN_NOT_OK(PairwiseExecImpl(ctx, batch[0].array, state.scalar_exec, 
state.periods,
+                                 out->array_data_mutable()));
+  return Status::OK();
+}
+
+const FunctionDoc pairwise_diff_doc(
+    "Compute first order difference of an array",
+    ("Computes the first order difference of an array, It internally calls \n"
+     "the scalar function \"subtract\" to compute \n differences, so its \n"
+     "behavior and supported types are the same as \n"
+     "\"subtract\". The period can be specified in 
:struct:`PairwiseOptions`.\n"
+     "\n"
+     "Results will wrap around on integer overflow. Use function \n"
+     "\"pairwise_diff_checked\" if you want overflow to return an error."),
+    {"input"}, "PairwiseOptions");
+
+const FunctionDoc pairwise_diff_checked_doc(
+    "Compute first order difference of an array",
+    ("Computes the first order difference of an array, It internally calls \n"
+     "the scalar function \"subtract_checked\" (or the checked variant) to 
compute \n"
+     "differences, so its behavior and supported types are the same as \n"
+     "\"subtract_checked\". The period can be specified in 
:struct:`PairwiseOptions`.\n"
+     "\n"
+     "This function returns an error on overflow. For a variant that doesn't 
\n"
+     "fail on overflow, use function \"pairwise_diff\"."),
+    {"input"}, "PairwiseOptions");
+
+const PairwiseOptions* GetDefaultPairwiseOptions() {
+  static const auto kDefaultPairwiseOptions = PairwiseOptions::Defaults();
+  return &kDefaultPairwiseOptions;
+}
+
+struct PairwiseKernelData {
+  InputType input;
+  OutputType output;
+  ArrayKernelExec exec;
+};
+
+void RegisterPairwiseDiffKernels(std::string_view func_name,
+                                 std::string_view base_func_name, const 
FunctionDoc& doc,
+                                 FunctionRegistry* registry) {
+  VectorKernel base_kernel;

Review Comment:
   Updated. Sorry for the confusion!



##########
cpp/src/arrow/compute/kernels/vector_pairwise.cc:
##########
@@ -0,0 +1,182 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+// Vector kernels for pairwise computation
+
+#include <iostream>
+#include <memory>
+#include "arrow/builder.h"
+#include "arrow/compute/api_vector.h"
+#include "arrow/compute/exec.h"
+#include "arrow/compute/function.h"
+#include "arrow/compute/kernel.h"
+#include "arrow/compute/kernels/base_arithmetic_internal.h"
+#include "arrow/compute/kernels/codegen_internal.h"
+#include "arrow/compute/registry.h"
+#include "arrow/compute/util.h"
+#include "arrow/status.h"
+#include "arrow/type.h"
+#include "arrow/type_fwd.h"
+#include "arrow/type_traits.h"
+#include "arrow/util/bit_util.h"
+#include "arrow/util/checked_cast.h"
+#include "arrow/util/logging.h"
+#include "arrow/visit_type_inline.h"
+
+namespace arrow::compute::internal {
+
+// We reuse the kernel exec function of a scalar binary function to compute 
pairwise
+// results. For example, for pairwise_diff, we reuse subtract's kernel exec.
+struct PairwiseState : KernelState {
+  PairwiseState(const PairwiseOptions& options, const ArrayKernelExec& 
scalar_exec)
+      : periods(options.periods), scalar_exec(scalar_exec) {}
+
+  int64_t periods;
+  const ArrayKernelExec& scalar_exec;
+};
+
+KernelInit GeneratePairwiseInit(const ArrayKernelExec& scalar_exec) {
+  return [&scalar_exec](KernelContext* ctx, const KernelInitArgs& args) {
+    return std::make_unique<PairwiseState>(
+        checked_cast<const PairwiseOptions&>(*args.options), scalar_exec);
+  };
+}
+
+/// A generic pairwise implementation that can be reused by different ops.
+Status PairwiseExecImpl(KernelContext* ctx, const ArraySpan& input,
+                        const ArrayKernelExec& scalar_exec, int64_t periods,
+                        ArrayData* result) {
+  auto offset = abs(periods);
+  offset = std::min(offset, input.length);
+  auto exec_length = input.length - offset;
+  // prepare bitmap
+  auto null_start = periods > 0 ? 0 : exec_length;
+  auto non_null_start = periods > 0 ? offset : 0;
+  bit_util::ClearBitmap(result->buffers[0]->mutable_data(), null_start, 
offset);
+  for (int64_t i = non_null_start; i < non_null_start + exec_length; i++) {
+    if (input.IsValid(i) && input.IsValid(i - periods)) {
+      bit_util::SetBit(result->buffers[0]->mutable_data(), i);
+    } else {
+      bit_util::ClearBit(result->buffers[0]->mutable_data(), i);
+    }
+  }
+  // prepare input span
+  ArraySpan left(input);
+  left.SetSlice(periods > 0 ? offset : 0, exec_length);
+  ArraySpan right(input);
+  right.SetSlice(periods > 0 ? 0 : offset, exec_length);
+  // prepare output span
+  ArraySpan output_span;
+  output_span.SetMembers(*result);
+  output_span.offset = periods > 0 ? offset : 0;
+  output_span.length = exec_length;
+  ExecResult output{output_span};
+  // execute scalar function
+  RETURN_NOT_OK(scalar_exec(ctx, ExecSpan({left, right}, exec_length), 
&output));
+
+  return Status::OK();
+}
+
+Status PairwiseExec(KernelContext* ctx, const ExecSpan& batch, ExecResult* 
out) {
+  const auto& state = checked_cast<const PairwiseState&>(*ctx->state());
+  auto input = batch[0].array;
+  RETURN_NOT_OK(PairwiseExecImpl(ctx, batch[0].array, state.scalar_exec, 
state.periods,
+                                 out->array_data_mutable()));
+  return Status::OK();
+}
+
+const FunctionDoc pairwise_diff_doc(
+    "Compute first order difference of an array",
+    ("Computes the first order difference of an array, It internally calls \n"
+     "the scalar function \"subtract\" to compute \n differences, so its \n"
+     "behavior and supported types are the same as \n"
+     "\"subtract\". The period can be specified in 
:struct:`PairwiseOptions`.\n"
+     "\n"
+     "Results will wrap around on integer overflow. Use function \n"
+     "\"pairwise_diff_checked\" if you want overflow to return an error."),
+    {"input"}, "PairwiseOptions");
+
+const FunctionDoc pairwise_diff_checked_doc(
+    "Compute first order difference of an array",
+    ("Computes the first order difference of an array, It internally calls \n"
+     "the scalar function \"subtract_checked\" (or the checked variant) to 
compute \n"
+     "differences, so its behavior and supported types are the same as \n"
+     "\"subtract_checked\". The period can be specified in 
:struct:`PairwiseOptions`.\n"
+     "\n"
+     "This function returns an error on overflow. For a variant that doesn't 
\n"
+     "fail on overflow, use function \"pairwise_diff\"."),
+    {"input"}, "PairwiseOptions");
+
+const PairwiseOptions* GetDefaultPairwiseOptions() {
+  static const auto kDefaultPairwiseOptions = PairwiseOptions::Defaults();
+  return &kDefaultPairwiseOptions;
+}
+
+struct PairwiseKernelData {
+  InputType input;
+  OutputType output;
+  ArrayKernelExec exec;
+};
+
+void RegisterPairwiseDiffKernels(std::string_view func_name,
+                                 std::string_view base_func_name, const 
FunctionDoc& doc,
+                                 FunctionRegistry* registry) {
+  VectorKernel base_kernel;
+  base_kernel.can_execute_chunkwise = false;
+  base_kernel.null_handling = NullHandling::COMPUTED_PREALLOCATE;
+  base_kernel.mem_allocation = MemAllocation::PREALLOCATE;
+  base_kernel.init = OptionsWrapper<PairwiseOptions>::Init;
+  auto func = std::make_shared<VectorFunction>(std::string(func_name), 
Arity::Unary(),
+                                               doc, 
GetDefaultPairwiseOptions());
+
+  auto base_func_result = registry->GetFunction(std::string(base_func_name));
+  DCHECK_OK(base_func_result.status());
+  const auto& base_func = checked_cast<const 
ScalarFunction&>(**base_func_result);
+  DCHECK_EQ(base_func.arity().num_args, 2);
+
+  for (const auto& base_func_kernel : base_func.kernels()) {
+    const auto& base_func_kernel_sig = base_func_kernel->signature;
+    if 
(base_func_kernel_sig->in_types()[0].Equals(base_func_kernel_sig->in_types()[1]))
 {

Review Comment:
   Updated



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