atefsawaed commented on code in PR #1621:
URL: https://github.com/apache/arrow-rs/pull/1621#discussion_r861667292
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parquet/src/column/writer.rs:
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@@ -1049,6 +1084,54 @@ fn has_dictionary_support(kind: Type, props:
&WriterProperties) -> bool {
}
}
+/// Signed comparison of bytes arrays
+fn compare_greater_byte_array_decimals(a: &[u8], b: &[u8]) -> bool {
+ let a_length = a.len();
+ let b_length = b.len();
+
+ if a_length == 0 || b_length == 0 {
+ return a_length > 0 && b_length == 0;
+ }
+
+ let first_a: u8 = a[0];
+ let first_b: u8 = b[0];
+
+ // We can short circuit for different signed numbers or
+ // for equal length bytes arrays that have different first bytes.
+ // The equality requirement is necessary for sign extension cases.
+ // 0xFF10 should be equal to 0x10 (due to big endian sign extension).
+ if (0x80 & first_a) != (0x80 & first_b)
+ || (a_length == b_length && first_a != first_b)
+ {
+ return (first_a as i8) > (first_b as i8);
+ }
+
+ // When the lengths are unequal and the numbers are of the same
+ // sign we need to do comparison by sign extending the shorter
+ // value first, and once we get to equal sized arrays, lexicographical
+ // unsigned comparison of everything but the first byte is sufficient.
+
+ let extension: u8 = if (first_a as i8) < 0 { 0xFF } else { 0 };
+
+ if a_length != b_length {
+ let not_equal = if a_length > b_length {
+ let lead_length = a_length - b_length;
+ Some((&a[0..lead_length]).iter().any(|&x| x != extension))
+ } else {
+ let lead_length = b_length - a_length;
+ Some((&b[0..lead_length]).iter().any(|&x| x != extension))
+ };
+
+ if not_equal.unwrap() {
+ let negative_values: bool = (first_a as i8) < 0;
+ let a_longer: bool = a_length > b_length;
+ return if negative_values { !a_longer } else { a_longer };
+ }
+ }
+
+ (a[1..]) > (b[1..])
Review Comment:
No, in this case the lexicographical unsigned comparison of both buffers is
sufficient.
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