pitrou commented on code in PR #13768:
URL: https://github.com/apache/arrow/pull/13768#discussion_r936950524
##########
go/arrow/bitutil/bitmaps.go:
##########
@@ -422,3 +423,81 @@ func CopyBitmap(src []byte, srcOffset, length int, dst
[]byte, dstOffset int) {
dst[nbytes-1] &= ^trailMask
dst[nbytes-1] |= lastData & trailMask
}
+
+type bitOp struct {
+ opWord func(uint64, uint64) uint64
+ opByte func(byte, byte) byte
+}
+
+var (
+ bitAndOp = bitOp{
+ opWord: func(l, r uint64) uint64 { return l & r },
+ opByte: func(l, r byte) byte { return l & r },
+ }
+ bitOrOp = bitOp{
+ opWord: func(l, r uint64) uint64 { return l | r },
+ opByte: func(l, r byte) byte { return l | r },
+ }
+)
+
+func alignedBitmapOp(op bitOp, left, right []byte, lOffset, rOffset int64, out
[]byte, outOffset int64, length int64) {
+ debug.Assert(lOffset%8 == rOffset%8, "aligned bitmap op called with
unaligned offsets")
+ debug.Assert(lOffset%8 == outOffset%8, "aligned bitmap op called with
unaligned output offset")
+
+ nbytes := BytesForBits(length + lOffset%8)
+ left = left[lOffset/8:]
+ right = right[rOffset/8:]
+ out = out[outOffset/8:]
+ for i := int64(0); i < nbytes; i++ {
+ out[i] = op.opByte(left[i], right[i])
+ }
+}
+
+func unalignedBitmapOp(op bitOp, left, right []byte, lOffset, rOffset int64,
out []byte, outOffset int64, length int64) {
+ leftRdr := NewBitmapWordReader(left, int(lOffset), int(length))
+ rightRdr := NewBitmapWordReader(right, int(rOffset), int(length))
+ writer := NewBitmapWordWriter(out, int(outOffset), int(length))
+
+ for nwords := leftRdr.Words(); nwords > 0; nwords-- {
+ writer.PutNextWord(op.opWord(leftRdr.NextWord(),
rightRdr.NextWord()))
Review Comment:
Well, if I run the C++ benchmarks, I get this:
```
BenchmarkBitmapAnd/32768/0 1696 ns 1696 ns
411775 bytes_per_second=17.9927G/s
BenchmarkBitmapAnd/131072/0 6843 ns 6842 ns
101856 bytes_per_second=17.8405G/s
BenchmarkBitmapAnd/32768/1 3999 ns 3998 ns
174766 bytes_per_second=7.63287G/s
BenchmarkBitmapAnd/131072/1 15546 ns 15544 ns
44802 bytes_per_second=7.85325G/s
BenchmarkBitmapAnd/32768/2 3988 ns 3987 ns
175050 bytes_per_second=7.65504G/s
BenchmarkBitmapAnd/131072/2 15601 ns 15599 ns
44678 bytes_per_second=7.82568G/s
```
... where the first benchmark parameter is the number of bytes and the
second is the bif offset, so you see the results show a similar performance
profile as the Go ones (with the aligned implementation being a couple times
faster than the unaligned one).
The reason this works is probably that C++ compilers optimize hard enough to
turn the byte-wise loop into a word-wise loop plus byte-wise prolog/epilog.
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