[Feature] Unpack predicate boolean kernel bitmaps a byte at a time

src/paimon/common/utils/arrow/ から始めて、MultiLiteralsLeafFunction と NullFalseLeafBinaryFunction を見つけ、既存の bitmap-to-byte ループを LeafFunction::Test まで追跡します。共有 helper と、すべての offset と length、両方の negate 値、バイト境界に揃っていない validity 期間を網羅する property test を追加します。helper が行ごとの accessor reference と一致し、両方の caller が変更されていない bytes を返せば完了です。

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Motivation

Two predicate leaf functions evaluate a batch by running an arrow::compute kernel and reading back the arrow::BooleanArray it writes: MultiLiteralsLeafFunction (IN / NOT IN, via IsIn) and NullFalseLeafBinaryFunction (the comparison functions). A kernel returns a bitmap, one bit per row, but LeafFunction::Test returns std::vector<char>, one byte per row, so both call sites spread the bits over bytes with the same per-row loop: test IsNull, read Value, apply the negation NOT IN needs, store a byte. That is a shift, a mask and a byte store per row, duplicated across the two call sites, on the selection path every filtered batch goes through.

Solution

Extract the spread into one helper, ArrowUtils::UnpackBooleansToBytes(array, negate), and read the bitmap a byte at a time instead of a bit at a time:

• A compile-time table maps each of the 256 bitmap bytes to the eight bytes it expands to, so the aligned body produces eight rows per iteration with one lookup and one 8-byte store.
• A scalar head and tail cover the rows sharing a partial leading or trailing byte, which is where the array offset is not byte-aligned; a batch a kernel has just written is aligned, so it takes the fast body throughout.
• The offset and the validity bitmap are honoured exactly as BooleanArray::Value() and Array::IsValid() honour them, and a null row unpacks to 0 whatever the value bitmap holds for it, which is what both IN / NOT IN and every NullFalseLeafBinaryFunction require.

MultiLiteralsLeafFunction passes its negate through; NullFalseLeafBinaryFunction passes negate=false. The bytes each returns are unchanged.

Anything else?

A property test that asserts the helper equals a row-by-row reference through the very accessors it replaces, over every (offset, length) slice of a bitmap whose value and null periods are not multiples of eight and both negate values, pins the offset, validity and negate handling against the definitions it optimizes. No change to any header under include/paimon/, the storage format, or the protocol: ArrowUtils is an internal utility under src/paimon/common/utils/arrow/.

Are you willing to submit a PR?

• I'm willing to submit a PR!