From 49838858eab984fc4a7e8595d7dd1883b00350ea Mon Sep 17 00:00:00 2001
From: sgilmore10 <74676073+sgilmore10@users.noreply.github.com>
Date: Thu, 9 Nov 2023 11:14:31 -0500
Subject: [PATCH] GH-38630: [MATLAB] `arrow.array.BooleanArray`'s `toMATLAB`
 method does not take slice offsets into account (#38636)

### Rationale for this change

While working on #38415, I noticed that the `toMATLAB` method of `arrow.array.BooleanArray` does not take the slice offset into account. This will cause the `toMATLAB` method to return the wrong value.

### What changes are included in this PR?

1. Updated `arrow::matlab::bit::unpack` function to accept a `start_offset` as input.
2. Updated clients (`BooleanArray::toMATLAB` and `Array::getValid`) to supply the array `offset` as the `start_offset`.

### Are these changes tested?

The existing tests cover these changes. Additionally, the changes for #38415 will include tests that verify the `toMATLAB` method returns the correct MATLAB array when the underlying Arrow array has been sliced.

### Are there any user-facing changes?

No.

* Closes: #38630

Authored-by: Sarah Gilmore <sgilmore@mathworks.com>
Signed-off-by: Kevin Gurney <kgurney@mathworks.com>
---
 matlab/src/cpp/arrow/matlab/array/proxy/array.cc         | 2 +-
 matlab/src/cpp/arrow/matlab/array/proxy/boolean_array.cc | 2 +-
 matlab/src/cpp/arrow/matlab/bit/unpack.cc                | 3 +--
 matlab/src/cpp/arrow/matlab/bit/unpack.h                 | 2 +-
 4 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/matlab/src/cpp/arrow/matlab/array/proxy/array.cc b/matlab/src/cpp/arrow/matlab/array/proxy/array.cc
index 4e52c990d3eae..09d9473df4795 100644
--- a/matlab/src/cpp/arrow/matlab/array/proxy/array.cc
+++ b/matlab/src/cpp/arrow/matlab/array/proxy/array.cc
@@ -100,7 +100,7 @@ namespace arrow::matlab::array::proxy {
         }
 
         auto validity_bitmap = array->null_bitmap();
-        auto valid_elements_mda = bit::unpack(validity_bitmap, array_length);
+        auto valid_elements_mda = bit::unpack(validity_bitmap, array_length, array->offset());
         context.outputs[0] = valid_elements_mda;
     }
 
diff --git a/matlab/src/cpp/arrow/matlab/array/proxy/boolean_array.cc b/matlab/src/cpp/arrow/matlab/array/proxy/boolean_array.cc
index 6a6e478274823..da3560ce522f3 100644
--- a/matlab/src/cpp/arrow/matlab/array/proxy/boolean_array.cc
+++ b/matlab/src/cpp/arrow/matlab/array/proxy/boolean_array.cc
@@ -53,7 +53,7 @@ namespace arrow::matlab::array::proxy {
         void BooleanArray::toMATLAB(libmexclass::proxy::method::Context& context) {
             auto array_length = array->length();
             auto packed_logical_data_buffer = std::static_pointer_cast<arrow::BooleanArray>(array)->values();
-            auto logical_array_mda = bit::unpack(packed_logical_data_buffer, array_length);
+            auto logical_array_mda = bit::unpack(packed_logical_data_buffer, array_length, array->offset());
             context.outputs[0] = logical_array_mda;
         }
 }
diff --git a/matlab/src/cpp/arrow/matlab/bit/unpack.cc b/matlab/src/cpp/arrow/matlab/bit/unpack.cc
index 7135d593cf752..6cc88d48ede43 100644
--- a/matlab/src/cpp/arrow/matlab/bit/unpack.cc
+++ b/matlab/src/cpp/arrow/matlab/bit/unpack.cc
@@ -20,7 +20,7 @@
 #include "arrow/util/bitmap_visit.h"
 
 namespace arrow::matlab::bit {
-    ::matlab::data::TypedArray<bool> unpack(const std::shared_ptr<arrow::Buffer>& packed_buffer, int64_t length) {
+    ::matlab::data::TypedArray<bool> unpack(const std::shared_ptr<arrow::Buffer>& packed_buffer, int64_t length, int64_t start_offset) {
         const auto packed_buffer_ptr = packed_buffer->data();
 
         ::matlab::data::ArrayFactory factory;
@@ -31,7 +31,6 @@ namespace arrow::matlab::bit {
         auto unpacked_buffer_ptr = unpacked_buffer.get();
         auto visitFcn = [&](const bool is_valid) { *unpacked_buffer_ptr++ = is_valid; };
 
-        const int64_t start_offset = 0;
         arrow::internal::VisitBitsUnrolled(packed_buffer_ptr, start_offset, length, visitFcn);
 
         ::matlab::data::TypedArray<bool> unpacked_matlab_logical_Array = factory.createArrayFromBuffer({array_length, 1}, std::move(unpacked_buffer));
diff --git a/matlab/src/cpp/arrow/matlab/bit/unpack.h b/matlab/src/cpp/arrow/matlab/bit/unpack.h
index b6debb85f837b..6cd633e76fa56 100644
--- a/matlab/src/cpp/arrow/matlab/bit/unpack.h
+++ b/matlab/src/cpp/arrow/matlab/bit/unpack.h
@@ -22,6 +22,6 @@
 #include "MatlabDataArray.hpp"
 
 namespace arrow::matlab::bit {
-    ::matlab::data::TypedArray<bool> unpack(const std::shared_ptr<arrow::Buffer>& packed_buffer, int64_t length);
+    ::matlab::data::TypedArray<bool> unpack(const std::shared_ptr<arrow::Buffer>& packed_buffer, int64_t length, int64_t start_offset);
     const uint8_t* extract_ptr(const ::matlab::data::TypedArray<bool>& unpacked_validity_bitmap);
 }