pjfanning commented on code in PR #3430:
URL: https://github.com/apache/pekko/pull/3430#discussion_r3789092237
##########
actor/src/main/scala/org/apache/pekko/util/ByteString.scala:
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@@ -1393,15 +1393,29 @@ object ByteString {
if (offset + java.lang.Long.BYTES <= firstLen)
first.readLongBEUnchecked(offset)
else if (offset >= firstLen) second.readLongBEUnchecked(offset -
firstLen)
else {
- SWARUtil.getLongBE(
- byteAt(offset, firstLen),
- byteAt(offset + 1, firstLen),
- byteAt(offset + 2, firstLen),
- byteAt(offset + 3, firstLen),
- byteAt(offset + 4, firstLen),
- byteAt(offset + 5, firstLen),
- byteAt(offset + 6, firstLen),
- byteAt(offset + 7, firstLen))
+ // Cross-boundary: build two sub-longs from byteAtUnchecked and
combine.
+ // byteAtUnchecked is a single virtual call per byte (no extra branch
per byte),
+ // and the Long assembly is pure arithmetic with no per-byte branching.
+ val split = firstLen - offset // bytes in first fragment (1-7)
+ val firstPart = {
+ var i = offset
+ var v = 0L
+ while (i < firstLen) {
+ v = (v << 8) | (first.byteAtUnchecked(i).toLong & 0xFF)
+ i += 1
+ }
+ v << ((8 - split) << 3)
+ }
Review Comment:
the code is very similar but the split logic is different - it will be hard
to move this code to share it without affecting performance.
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