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=act clean up ByteString#drop(...) (#21440)

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* =act clean up ByteString#drop(...)

Current implementation has a good algorithm but seems a little bit complicated.

Clening-up does not suffer the performance (actually seems to have the better
performance when dropping(N-1)) where N is the length, and is easy to understand
almost the same algorithm now.

* Change private[akka] to priavte

* Rename go(...) and some variables

They should be easy for us to understand what they are.

* Add benchmark of ByteString#drop(...)
This commit is contained in:
monkey-mas 2016-10-05 23:25:34 +09:00 • committed by Konrad Malawski
parent cc845c84b0
commit 19dbe9a487
3 changed files with 150 additions and 70 deletions
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40
akka-actor/src/main/scala/akka/util/ByteString.scala
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@ -485,32 +485,24 @@ object ByteString {
else drop0(n)
private def drop0(n: Int): ByteString = {
var continue = true
var fullDrops = 0
var remainingToDrop = n
do {
// impl note: could be optimised a bit by using VectorIterator instead,
// however then we're forced to call .toVector which halfs performance
// We can work around that, as there's a Scala private method "remainingVector" which is fast,
// but let's not go into calling private APIs here just yet.
val currentLength = bytestrings(fullDrops).length
if (remainingToDrop >= currentLength) {
fullDrops += 1
remainingToDrop -= currentLength
} else continue = false
} while (remainingToDrop > 0 && continue)
// impl note: could be optimised a bit by using VectorIterator instead,
// however then we're forced to call .toVector which halfs performance
// We can work around that, as there's a Scala private method "remainingVector" which is fast,
// but let's not go into calling private APIs here just yet.
@tailrec def findSplit(fullDrops: Int, remainingToDrop: Int): (Int, Int) = {
val bs = bytestrings(fullDrops)
if (bs.length > remainingToDrop) (fullDrops, remainingToDrop)
else findSplit(fullDrops + 1, remainingToDrop - bs.length)
}
val remainingByteStrings = bytestrings.drop(fullDrops)
if (remainingByteStrings.isEmpty) ByteString.empty
else if (remainingToDrop > 0) {
val h: ByteString1 = remainingByteStrings.head.drop1(remainingToDrop)
val bs = remainingByteStrings.tail
val (fullDrops, remainingToDrop) = findSplit(0, n)
if (h.isEmpty)
if (bs.isEmpty) ByteString.empty
else new ByteStrings(bs, length - n)
else new ByteStrings(h +: bs, length - n)
} else ByteStrings(remainingByteStrings, length - n)
if (remainingToDrop == 0)
new ByteStrings(bytestrings.drop(fullDrops), length - n)
else if (fullDrops == bytestrings.length - 1)
bytestrings(fullDrops).drop(remainingToDrop)
else
new ByteStrings(bytestrings(fullDrops).drop1(remainingToDrop) +: bytestrings.drop(fullDrops + 1), length - n)
}
protected def writeReplace(): AnyRef = new SerializationProxy(this)