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perf: skip UTF-8 encode for clean-ASCII long strings in renderer #866

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perf: skip UTF-8 encode for clean-ASCII long strings in renderer #866

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10 changes: 10 additions & 0 deletions sjsonnet/src/sjsonnet/BaseByteRenderer.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -305,8 +305,18 @@ class BaseByteRenderer[T <: java.io.OutputStream](
/**
* SWAR-accelerated path for long strings. Converts to UTF-8 bytes once, then bulk-copies clean
* chunks and escapes only the bytes that require it.
*
* Probes the string with a SWAR ASCII-safe scan first. When the string is clean printable ASCII
* (no escape chars, no non-ASCII), the entire UTF-8 encode pass (HeapCharBuffer.wrap +
* CharsetEncoder.loop + output byte[] allocation) is skipped — bytes are written directly from
* the chars via Platform.copyAsciiStringToBytes. This is the dominant case for K8s/JSON output
* where long values (descriptions, paths, base64 blobs) are pure ASCII.
*/
private def visitLongString(str: String): Unit = {
if (Platform.isAsciiJsonSafe(str)) {
renderAsciiSafeString(str)
return
}
val bytes = str.getBytes(java.nio.charset.StandardCharsets.UTF_8)
val bLen = bytes.length
val firstEscape = CharSWAR.findFirstEscapeChar(bytes, 0, bLen)
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