alamb commented on code in PR #6288:
URL: https://github.com/apache/arrow-rs/pull/6288#discussion_r1758949806
##########
arrow-buffer/src/util/bit_mask.rs:
##########
@@ -30,35 +29,128 @@ pub fn set_bits(
offset_read: usize,
len: usize,
) -> usize {
+ assert!(offset_write + len <= write_data.len() * 8);
+ assert!(offset_read + len <= data.len() * 8);
let mut null_count = 0;
-
- let mut bits_to_align = offset_write % 8;
- if bits_to_align > 0 {
- bits_to_align = std::cmp::min(len, 8 - bits_to_align);
+ let mut acc = 0;
+ while len > acc {
+ // SAFETY: the arguments to `set_upto_64bits` are within the valid
range because
+ // (offset_write + acc) + (len - acc) == offset_write + len <=
write_data.len() * 8
+ // (offset_read + acc) + (len - acc) == offset_read + len <=
data.len() * 8
+ let (n, len_set) = unsafe {
+ set_upto_64bits(
+ write_data,
+ data,
+ offset_write + acc,
+ offset_read + acc,
+ len - acc,
+ )
+ };
+ null_count += n;
+ acc += len_set;
}
- let mut write_byte_index = ceil(offset_write + bits_to_align, 8);
-
- // Set full bytes provided by bit chunk iterator (which iterates in 64
bits at a time)
- let chunks = BitChunks::new(data, offset_read + bits_to_align, len -
bits_to_align);
- chunks.iter().for_each(|chunk| {
- null_count += chunk.count_zeros();
- write_data[write_byte_index..write_byte_index +
8].copy_from_slice(&chunk.to_le_bytes());
- write_byte_index += 8;
- });
-
- // Set individual bits both to align write_data to a byte offset and the
remainder bits not covered by the bit chunk iterator
- let remainder_offset = len - chunks.remainder_len();
- (0..bits_to_align)
- .chain(remainder_offset..len)
- .for_each(|i| {
- if get_bit(data, offset_read + i) {
- set_bit(write_data, offset_write + i);
+
+ null_count
+}
+
+/// # Safety
Review Comment:
Could you please also update this documentation with a description of what
both the arguments and return value represent (if it is the same as `set_bits`
a reference to that function would be fine)
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