Dandandan commented on code in PR #14195:
URL: https://github.com/apache/datafusion/pull/14195#discussion_r1923260496
##########
datafusion/functions/src/unicode/reverse.rs:
##########
@@ -119,12 +119,21 @@ fn reverse_impl<'a, T: OffsetSizeTrait, V:
StringArrayType<'a>>(
) -> Result<ArrayRef> {
let mut builder =
GenericStringBuilder::<T>::with_capacity(string_array.len(), 1024);
- let mut reversed = String::new();
+ let mut string_buf = String::new();
for string in string_array.iter() {
if let Some(s) = string {
- reversed.extend(s.chars().rev());
- builder.append_value(&reversed);
- reversed.clear();
+ if s.is_ascii() {
+ // SAFETY: Since the original string was ASCII, reversing the
bytes still results in valid UTF-8.
+ let reversed = unsafe {
+ // reverse bytes directly since ASCII characters are
single bytes
+
String::from_utf8_unchecked(s.bytes().rev().collect::<Vec<u8>>())
Review Comment:
We could avoid a allocation here by copying into a `Vec<u8>` buffer
```
// slightly faster than using iterator
bytes_buf.extend(s.as_bytes())
bytes_buf.reverse()
...
bytes_buf.clear()
```
##########
datafusion/functions/src/unicode/reverse.rs:
##########
@@ -119,12 +119,21 @@ fn reverse_impl<'a, T: OffsetSizeTrait, V:
StringArrayType<'a>>(
) -> Result<ArrayRef> {
let mut builder =
GenericStringBuilder::<T>::with_capacity(string_array.len(), 1024);
- let mut reversed = String::new();
+ let mut string_buf = String::new();
for string in string_array.iter() {
if let Some(s) = string {
- reversed.extend(s.chars().rev());
- builder.append_value(&reversed);
- reversed.clear();
+ if s.is_ascii() {
+ // SAFETY: Since the original string was ASCII, reversing the
bytes still results in valid UTF-8.
+ let reversed = unsafe {
+ // reverse bytes directly since ASCII characters are
single bytes
+
String::from_utf8_unchecked(s.bytes().rev().collect::<Vec<u8>>())
Review Comment:
We could avoid a allocation here by copying into a `Vec<u8>` buffer
```
// slightly faster than using iterator `bytes`
bytes_buf.extend(s.as_bytes())
bytes_buf.reverse()
...
bytes_buf.clear()
```
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