rluvaton commented on code in PR #8653:
URL: https://github.com/apache/arrow-rs/pull/8653#discussion_r2444781020
##########
arrow-buffer/src/buffer/mutable.rs:
##########
@@ -222,6 +222,82 @@ impl MutableBuffer {
}
}
+ /// Creates a new [`MutableBuffer`] by repeating the contents of
`slice_to_repeat`
+ /// `repeat_count` times.
+ pub fn new_repeated<T: ArrowNativeType>(repeat_count: usize,
slice_to_repeat: &[T]) -> Self {
+ if slice_to_repeat.is_empty() || repeat_count == 0 {
+ return Self::new(0);
+ }
+
+ // If we keep extending from ourself we will reach it pretty fast
+ let value_len = slice_to_repeat.len();
+ let final_len = repeat_count * value_len;
+ let mut mutable = Self::with_capacity(final_len);
+
+ mutable.push_slice_repeated(repeat_count, slice_to_repeat);
+
+ mutable
+ }
+
+ /// Adding to this mutable buffer `slice_to_repeat` repeated
`repeat_count` times.
+ pub fn push_slice_repeated<T: ArrowNativeType>(
+ &mut self,
+ repeat_count: usize,
+ slice_to_repeat: &[T],
+ ) {
+ if repeat_count == 0 || slice_to_repeat.is_empty() {
+ return;
+ }
+
+ // Ensure capacity
+ let additional = repeat_count * mem::size_of_val(slice_to_repeat);
+ self.reserve(additional);
+
+ // No need to special case small repeat counts
+ if repeat_count <= 3 {
+ for _ in 0..repeat_count {
+ self.extend_from_slice(slice_to_repeat);
+ }
+
+ return;
+ }
+
+ // If we keep extending from ourself we will reach it pretty fast
+ let value_len = slice_to_repeat.len();
+ let final_len_to_repeat = repeat_count * value_len;
+
+ let length_before = self.len;
+
+ self.extend_from_slice(slice_to_repeat);
+ let mut added_repeats_length = mem::size_of_val(slice_to_repeat);
+
+ // Copy in doubling steps to reduce number of copy calls
+ while added_repeats_length * 2 <= final_len_to_repeat {
+ unsafe {
+ let src = self.data.as_ptr().add(length_before) as *const u8;
+ let dst = self.data.as_ptr().add(self.len);
+ std::ptr::copy_nonoverlapping(src, dst, added_repeats_length)
+ }
+ self.len += added_repeats_length;
+ added_repeats_length *= 2;
+ }
+
+ // Copy the rest of the required data in one go
+ let last_amount_to_copy = final_len_to_repeat - added_repeats_length;
+ assert!(
+ last_amount_to_copy <= final_len_to_repeat,
+ "the last copy should not overlap"
+ );
+
+ unsafe {
+ let src = self.data.as_ptr().add(length_before) as *const u8;
+ let dst = self.data.as_ptr().add(self.len);
+
+ std::ptr::copy_nonoverlapping(src, dst, last_amount_to_copy)
+ }
+ self.len += last_amount_to_copy;
Review Comment:
Extracted to:
- #8658
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