tustvold commented on a change in pull request #1054:
URL: https://github.com/apache/arrow-rs/pull/1054#discussion_r776324475
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File path: arrow/src/array/builder.rs
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@@ -398,6 +400,117 @@ impl BooleanBufferBuilder {
}
}
+ /// Append `count` bits from `to_set`
+ ///
+ /// `to_set` is a slice of bits packed LSB-first into `[u8]`
+ ///
+ /// # Panics
+ ///
+ /// Panics if `to_set` does not contain `ceil(count / 8)` bytes
+ #[inline]
+ pub fn append_packed(&mut self, count: usize, to_set: &[u8]) {
+ assert_eq!((count + 7) >> 3, to_set.len());
+
+ let new_len = self.len + count;
+ let new_buf_len = (new_len + 7) >> 3;
+ self.buffer.reserve(new_buf_len - self.buffer.len());
+
+ let whole_bytes = count >> 3;
+ let overrun = count & 7;
+
+ let skew = self.len & 7;
+ if skew == 0 {
+ self.buffer.extend_from_slice(&to_set[..whole_bytes]);
+ if overrun > 0 {
+ let masked = to_set[whole_bytes] & ((1 << overrun) - 1);
+ self.buffer.push(masked)
+ }
+
+ self.len = new_len;
+ debug_assert_eq!(self.buffer.len(), new_buf_len);
+ return;
+ }
+
+ for to_set_byte in &to_set[..whole_bytes] {
+ let low = *to_set_byte << skew;
+ let high = *to_set_byte >> (8 - skew);
+
+ *self.buffer.last_mut().unwrap() |= low;
Review comment:
I'd somewhat hope that LLVM would be smart enough to perform this
optimisation itself, will confirm this once I get to polishing this up for
final review in #1039
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