alamb commented on code in PR #6870:
URL: https://github.com/apache/arrow-rs/pull/6870#discussion_r1885862689
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parquet/src/column/writer/mod.rs:
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@@ -1418,13 +1438,51 @@ fn compare_greater_byte_array_decimals(a: &[u8], b:
&[u8]) -> bool {
(a[1..]) > (b[1..])
}
-/// Truncate a UTF8 slice to the longest prefix that is still a valid UTF8
string,
-/// while being less than `length` bytes and non-empty
+/// Truncate a UTF-8 slice to the longest prefix that is still a valid UTF-8
string,
+/// while being less than `length` bytes and non-empty. Returns `None` if
truncation
+/// is not possible within those constraints.
+///
+/// The caller guarantees that data.len() > length.
fn truncate_utf8(data: &str, length: usize) -> Option<Vec<u8>> {
let split = (1..=length).rfind(|x| data.is_char_boundary(*x))?;
Some(data.as_bytes()[..split].to_vec())
}
+/// Truncate a UTF-8 slice and increment it's final character. The returned
value is the
+/// longest such slice that is still a valid UTF-8 string while being less
than `length`
+/// bytes and non-empty. Returns `None` if no such transformation is possible.
+///
+/// The caller guarantees that data.len() > length.
+fn truncate_and_increment_utf8(data: &str, length: usize) -> Option<Vec<u8>> {
+ // UTF-8 is max 4 bytes, so start search 3 back from desired length
+ let lower_bound = length.saturating_sub(3);
+ let split = (lower_bound..=length).rfind(|x| data.is_char_boundary(*x))?;
+ increment_utf8(data.get(..split)?)
+}
+
+/// Increment the final character in a UTF-8 string in such a way that the
returned result
+/// is still a valid UTF-8 string. The returned string may be shorter than the
input if the
+/// last character(s) cannot be incremented (due to overflow or producing
invalid code points).
+/// Returns `None` if the string cannot be incremented.
+///
+/// Note that this implementation will not promote an N-byte code point to
(N+1) bytes.
+fn increment_utf8(data: &str) -> Option<Vec<u8>> {
+ for (idx, code_point) in data.char_indices().rev() {
+ let curr_len = code_point.len_utf8();
+ let original = code_point as u32;
+ if let Some(next_char) = char::from_u32(original + 1) {
+ // do not allow increasing byte width of incremented char
Review Comment:
I think what you have here (equality) is good and easy to reason about.
Let's keep it that way
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