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perf: render escaped byte strings in one pass #845

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perf: render escaped byte strings in one pass #845

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39 changes: 18 additions & 21 deletions sjsonnet/src/sjsonnet/BaseByteRenderer.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -319,9 +319,8 @@ class BaseByteRenderer[T <: java.io.OutputStream](
arr(pos + 1 + bLen) = '"'.toByte
elemBuilder.length = pos + bLen + 2
} else {
val escapedLen = escapedStringLength(bytes, bLen, firstEscape)
elemBuilder.ensureLength(escapedLen)
val arr = elemBuilder.arr
elemBuilder.ensureLength(bLen + 2 + (bLen >>> 5))
var arr = elemBuilder.arr
var outPos = elemBuilder.length
arr(outPos) = '"'.toByte
outPos += 1
Expand All @@ -330,41 +329,39 @@ class BaseByteRenderer[T <: java.io.OutputStream](
while (escPos >= 0) {
if (escPos > from) {
val chunkLen = escPos - from
elemBuilder.length = outPos
elemBuilder.ensureLength(chunkLen + 6)
arr = elemBuilder.arr
outPos = elemBuilder.length
System.arraycopy(bytes, from, arr, outPos, chunkLen)
outPos += chunkLen
}
elemBuilder.length = outPos
elemBuilder.ensureLength(6)
arr = elemBuilder.arr
outPos = elemBuilder.length
outPos = escapeByteInline(bytes(escPos) & 0xff, arr, outPos)
from = escPos + 1
escPos = if (from < bLen) CharSWAR.findFirstEscapeChar(bytes, from, bLen) else -1
}
if (from < bLen) {
val tailLen = bLen - from
elemBuilder.length = outPos
elemBuilder.ensureLength(tailLen + 1)
arr = elemBuilder.arr
outPos = elemBuilder.length
System.arraycopy(bytes, from, arr, outPos, tailLen)
outPos += tailLen
}
elemBuilder.length = outPos
elemBuilder.ensureLength(1)
arr = elemBuilder.arr
outPos = elemBuilder.length
arr(outPos) = '"'.toByte
elemBuilder.length = outPos + 1
}
}

private def escapedStringLength(bytes: Array[Byte], bLen: Int, firstEscape: Int): Int = {
var len = bLen + 2
var from = firstEscape
var escPos = firstEscape
while (escPos >= 0) {
len += escapeExtraLength(bytes(escPos) & 0xff)
from = escPos + 1
escPos = if (from < bLen) CharSWAR.findFirstEscapeChar(bytes, from, bLen) else -1
}
len
}

@inline private def escapeExtraLength(b: Int): Int =
(b: @scala.annotation.switch) match {
case '"' | '\\' | '\b' | '\f' | '\n' | '\r' | '\t' => 1
case _ => 5
}

/** Inline JSON escape for one byte that is known to require escaping. */
@inline private def escapeByteInline(b: Int, arr: Array[Byte], outPos0: Int): Int = {
val outPos = outPos0
Expand Down
8 changes: 8 additions & 0 deletions sjsonnet/test/src/sjsonnet/RendererTests.scala
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Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
package sjsonnet

import java.io.ByteArrayOutputStream
import utest._

object RendererTests extends TestSuite {
Expand Down Expand Up @@ -65,6 +66,13 @@ object RendererTests extends TestSuite {
ujson.transform(ujson.Num(1e15), new Renderer()).toString ==> "1000000000000000"
}

test("byteRendererLongEscapedString") {
val s = ("abc\n\"\\\t\u0001" * 40) + "tail"
val out = new ByteArrayOutputStream
ujson.transform(ujson.Str(s), new ByteRenderer(out))
out.toString("UTF-8") ==> ujson.transform(ujson.Str(s), new Renderer()).toString
}

test("indentZero") {
// indent=0 should produce newlines but no spaces
ujson.transform(ujson.Arr(1, 2), new Renderer(indent = 0)).toString ==>
Expand Down
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