Don't use unpack16

AntoinePrv · AntoinePrv · commit 0a52c0cc18ef · 2025-09-26T15:01:41.000+02:00
diff --git a/cpp/src/arrow/util/bit_stream_utils_internal.h b/cpp/src/arrow/util/bit_stream_utils_internal.h
@@ -323,7 +323,8 @@ inline int BitReader::GetBatch(int num_bits, T* v, int batch_size) {
     }
   }
 
-  if constexpr (sizeof(T) >= 2) {
+  // unpack for uint16_t not as fast as unpack for uint32_t + memcpy.
+  if constexpr (sizeof(T) >= sizeof(32)) {
     int num_unpacked = internal::unpack(buffer + byte_offset,
                                         reinterpret_cast<std::make_unsigned_t<T>*>(v + i),
                                         batch_size - i, num_bits);

Original file line number	Diff line number	Diff line change
`@@ -323,7 +323,8 @@ inline int BitReader::GetBatch(int num_bits, T* v, int batch_size) {`
`323`	`323`	`}`
`324`	`324`	`}`
`325`	`325`
`326`		`- if constexpr (sizeof(T) >= 2) {`
	`326`	`+ // unpack for uint16_t not as fast as unpack for uint32_t + memcpy.`
	`327`	`+ if constexpr (sizeof(T) >= sizeof(32)) {`
`327`	`328`	`int num_unpacked = internal::unpack(buffer + byte_offset,`
`328`	`329`	`reinterpret_cast<std::make_unsigned_t<T>*>(v + i),`
`329`	`330`	`batch_size - i, num_bits);`