[GitHub] [arrow-rs] tustvold commented on a diff in pull request #2883: Copying inappropriately aligned buffer in ipc reader

[GitBox <gi...@apache.org>]

tustvold commented on code in PR #2883:
URL: https://github.com/apache/arrow-rs/pull/2883#discussion_r996395378


##########
arrow/src/ipc/reader.rs:
##########
@@ -499,6 +500,34 @@ fn create_primitive_array(
     make_array(array_data)
 }
 
+/// Checks if given `Buffer` is properly aligned with `i128`.
+/// If not, copying the data and padded it for alignment.
+fn get_aligned_buffer(buffer: &Buffer, length: usize) -> Buffer {
+    let ptr = buffer.as_ptr();
+    let align_req = std::mem::align_of::<i128>();
+    let align_offset = ptr.align_offset(align_req);
+    // The buffer is not aligned properly. The writer might use a smaller alignment
+    // e.g. 8 bytes, but on some platform (e.g. ARM) i128 requires 16 bytes alignment.
+    // We need to copy the buffer as fallback.
+    if align_offset != 0 {
+        let len_in_bytes = length * std::mem::size_of::<i128>();
+        let pad_len = padding(len_in_bytes, align_req);
+        let mut aligned_buffer = MutableBuffer::with_capacity(len_in_bytes + pad_len);
+        aligned_buffer.extend_from_slice(&buffer.as_slice()[0..len_in_bytes]);
+        aligned_buffer.extend_from_slice(&vec![0u8; pad_len]);
+        aligned_buffer.into()
+    } else {
+        buffer.clone()
+    }
+}
+
+/// Calculate byte boundary and return the number of bytes needed to pad to `align_req` bytes
+#[inline]
+fn padding(len: usize, align_req: usize) -> usize {

Review Comment:
   This is already handled for you by MutableBuffer, you shouldn't need to add explicit padding



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