From a3a41bbc2b7be5416405620ef4d588c8fbcc2ae1 Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Mon, 22 Oct 2018 14:31:40 +0200
Subject: [PATCH 1/2] Improve compression of TastyString

Improves #3877

`'{ { val y = ~x * ~x; ~powerCode(n / 2, '(y)) } }`
was reduced from 206 bytes to 172 bytes

`'{ ~x * ~powerCode(n - 1, x) }`
was reduced from 143 bytes to 128 bytes
---
 .../tools/dotc/core/tasty/TastyString.scala   | 40 +++++++++----------
 1 file changed, 20 insertions(+), 20 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/core/tasty/TastyString.scala b/compiler/src/dotty/tools/dotc/core/tasty/TastyString.scala
index fe9f8cc0883d..5bb6a8456a1a 100644
--- a/compiler/src/dotty/tools/dotc/core/tasty/TastyString.scala
+++ b/compiler/src/dotty/tools/dotc/core/tasty/TastyString.scala
@@ -2,34 +2,34 @@ package dotty.tools.dotc.core.tasty
 
 import scala.runtime.quoted.Unpickler.Pickled
 
+import java.io._
+import java.util.Base64
+import java.nio.charset.StandardCharsets.UTF_8
+
 /** Utils for String representation of TASTY */
 object TastyString {
 
-  // Conservative encoding, each byte is encoded in a char
-  // TODO improve encoding compression
-  private final val maxStringSize = 65535 / 2
+  // Max size of a string literal in the bytecode
+  private final val maxStringSize = 65535
 
   /** Encode TASTY bytes into an Seq of String */
-  def pickle(bytes: Array[Byte]): Pickled =
-    bytes.sliding(maxStringSize, maxStringSize).map(bytesToString).toList
-
-  /** Decode the TASTY String into TASTY bytes */
-  def unpickle(strings: Pickled): Array[Byte] = {
-    val bytes = new Array[Byte](strings.map(_.length).sum)
-    var i = 0
-    for (str <- strings; j <- str.indices) {
-      bytes(i) = str.charAt(j).toByte
-      i += 1
+  def pickle(bytes: Array[Byte]): Pickled = {
+    val str = new String(Base64.getEncoder().encode(bytes), UTF_8)
+    def split(sliceEnd: Int, acc: List[String]): List[String] = {
+      if (sliceEnd == 0) acc
+      else {
+        val sliceStart = (sliceEnd - maxStringSize) max 0
+        split(sliceStart, str.substring(sliceStart, sliceEnd) :: acc)
+      }
     }
-    bytes
+    split(str.length, Nil)
   }
 
-  /** Encode bytes into a String */
-  private def bytesToString(bytes: Array[Byte]): String = {
-    assert(bytes.length <= maxStringSize)
-    val chars = new Array[Char](bytes.length)
-    for (i <- bytes.indices) chars(i) = (bytes(i) & 0xff).toChar
-    new String(chars)
+  /** Decode the TASTY String into TASTY bytes */
+  def unpickle(strings: Pickled): Array[Byte] = {
+    val string = new StringBuilder
+    strings.foreach(string.append)
+    Base64.getDecoder().decode(string.result().getBytes(UTF_8))
   }
 
 }

From 2f669956cdca6ac188dd77ad09dfcca77bf46988 Mon Sep 17 00:00:00 2001
From: Nicolas Stucki <nicolas.stucki@gmail.com>
Date: Tue, 23 Oct 2018 11:46:08 +0200
Subject: [PATCH 2/2] Use sliding to simplify the code

---
 .../src/dotty/tools/dotc/core/tasty/TastyString.scala    | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/core/tasty/TastyString.scala b/compiler/src/dotty/tools/dotc/core/tasty/TastyString.scala
index 5bb6a8456a1a..8450ee1f1a4c 100644
--- a/compiler/src/dotty/tools/dotc/core/tasty/TastyString.scala
+++ b/compiler/src/dotty/tools/dotc/core/tasty/TastyString.scala
@@ -15,14 +15,7 @@ object TastyString {
   /** Encode TASTY bytes into an Seq of String */
   def pickle(bytes: Array[Byte]): Pickled = {
     val str = new String(Base64.getEncoder().encode(bytes), UTF_8)
-    def split(sliceEnd: Int, acc: List[String]): List[String] = {
-      if (sliceEnd == 0) acc
-      else {
-        val sliceStart = (sliceEnd - maxStringSize) max 0
-        split(sliceStart, str.substring(sliceStart, sliceEnd) :: acc)
-      }
-    }
-    split(str.length, Nil)
+    str.sliding(maxStringSize, maxStringSize).toList
   }
 
   /** Decode the TASTY String into TASTY bytes */