From cf94433011792145740e7b4abed18ba93e21a5e2 Mon Sep 17 00:00:00 2001
From: Rusty Conover <rusty@conover.me>
Date: Sat, 5 Sep 2026 10:37:28 -0400
Subject: [PATCH] feat: add ArrowResolveChunk16

---
 src/nanoarrow/common/inline_buffer.h | 21 +++++++++++++++++++++
 src/nanoarrow/common/utils_test.cc   | 12 ++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/src/nanoarrow/common/inline_buffer.h b/src/nanoarrow/common/inline_buffer.h
index c9a78602b..e3d485475 100644
--- a/src/nanoarrow/common/inline_buffer.h
+++ b/src/nanoarrow/common/inline_buffer.h
@@ -71,6 +71,27 @@ static inline int64_t ArrowResolveChunk32(int32_t index, const int32_t* offsets,
   return lo;
 }
 
+static inline int64_t ArrowResolveChunk16(int16_t index, const int16_t* offsets,
+                                          int16_t lo, int16_t hi) {
+  // Similar to std::upper_bound(), but slightly different as our offsets
+  // array always starts with 0.
+  int16_t n = hi - lo;
+  // First iteration does not need to check for n > 1
+  // (lo < hi is guaranteed by the precondition).
+  NANOARROW_DCHECK(n > 1);
+  do {
+    const int16_t m = n >> 1;
+    const int16_t mid = lo + m;
+    if (index >= offsets[mid]) {
+      lo = mid;
+      n -= m;
+    } else {
+      n = m;
+    }
+  } while (n > 1);
+  return lo;
+}
+
 static inline int64_t _ArrowGrowByFactor(int64_t current_capacity, int64_t new_capacity) {
   int64_t doubled_capacity = current_capacity * 2;
   if (doubled_capacity > new_capacity) {
diff --git a/src/nanoarrow/common/utils_test.cc b/src/nanoarrow/common/utils_test.cc
index 0f8b0218e..d4e43ad57 100644
--- a/src/nanoarrow/common/utils_test.cc
+++ b/src/nanoarrow/common/utils_test.cc
@@ -783,6 +783,18 @@ TEST(UtilsTest, ArrowResolveChunk32Test) {
   EXPECT_EQ(ArrowResolveChunk32(5, offsets, 0, n_offsets), 2);
 }
 
+TEST(UtilsTest, ArrowResolveChunk16Test) {
+  int16_t offsets[] = {0, 2, 3, 6};
+  int16_t n_offsets = 4;
+
+  EXPECT_EQ(ArrowResolveChunk16(0, offsets, 0, n_offsets), 0);
+  EXPECT_EQ(ArrowResolveChunk16(1, offsets, 0, n_offsets), 0);
+  EXPECT_EQ(ArrowResolveChunk16(2, offsets, 0, n_offsets), 1);
+  EXPECT_EQ(ArrowResolveChunk16(3, offsets, 0, n_offsets), 2);
+  EXPECT_EQ(ArrowResolveChunk16(4, offsets, 0, n_offsets), 2);
+  EXPECT_EQ(ArrowResolveChunk16(5, offsets, 0, n_offsets), 2);
+}
+
 TEST(MaybeTest, ConstructionAndConversion) {
   using nanoarrow::NA;
   using nanoarrow::internal::Maybe;