From 340dc52a567de022c56acb1533c5772d21405f2a Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Sun, 8 Feb 2015 10:06:43 +0100
Subject: First prototype of pickler.

---
 .../tools/dotc/core/pickling/TreeBuffer.scala      | 133 +++++++++++++++++++++
 1 file changed, 133 insertions(+)
 create mode 100644 src/dotty/tools/dotc/core/pickling/TreeBuffer.scala

(limited to 'src/dotty/tools/dotc/core/pickling/TreeBuffer.scala')

diff --git a/src/dotty/tools/dotc/core/pickling/TreeBuffer.scala b/src/dotty/tools/dotc/core/pickling/TreeBuffer.scala
new file mode 100644
index 000000000..5a445124d
--- /dev/null
+++ b/src/dotty/tools/dotc/core/pickling/TreeBuffer.scala
@@ -0,0 +1,133 @@
+package dotty.tools
+package dotc
+package core
+package pickling
+
+import util.Util.{bestFit, dble}
+import TastyBuffer.{Addr, AddrWidth}
+
+class TreeBuffer extends TastyBuffer(1000000) {
+
+  private final val ItemsOverOffsets = 2
+    
+  private val initialOffsetSize = bytes.length / (AddrWidth * ItemsOverOffsets)
+  private var offsets = new Array[Int](initialOffsetSize)
+  private var isRelative = new Array[Boolean](initialOffsetSize)
+  private var delta: Array[Int] = _
+  private var numOffsets = 0
+            
+  private def offset(i: Int): Addr = new Addr(offsets(i))
+
+  private def keepOffset(relative: Boolean): Unit = {
+    if (numOffsets == offsets.length) {
+      offsets = dble(offsets)
+      isRelative = dble(isRelative)
+    }
+    offsets(numOffsets) = length
+    isRelative(numOffsets) = relative
+    numOffsets += 1
+  }
+       
+  def reserveRef(relative: Boolean): Addr = {
+    val addr = currentAddr
+    keepOffset(relative)
+    reserveAddr()
+    addr
+  }
+
+  def writeRef(target: Addr) = {
+    keepOffset(relative = false)
+    writeNat(target.index)
+  }
+  
+  def fillRef(at: Addr, target: Addr, relative: Boolean) = {
+    val addr = if (relative) target.relativeTo(at) else target
+    fillAddr(at, addr)
+  }
+    
+  def adjusted(x: Addr): Addr = {
+    val idx = bestFit(offsets, x.index - 1)
+    if (idx < 0) x else x - delta(idx)
+  }
+
+  private def computeDeltas() = {
+    delta = new Array[Int](numOffsets)
+    var lastDelta = 0
+    var i = 0
+    while (i < numOffsets) {
+      val off = offset(i)
+      val skippedOff = skipZeroes(off)
+      val skippedCount = skippedOff.index - off.index
+      assert(skippedCount < AddrWidth, s"unset field at position $off")
+      lastDelta += skippedCount
+      delta(i) = lastDelta 
+      i += 1
+    }
+  }
+  
+  private def adjustedOffset(at: Addr, isRelative: Boolean): Addr = {
+    val original = getAddr(at)
+    if (isRelative) {
+      val start = skipNat(at).index
+      adjusted(original + start) - start
+    } else adjusted(original)
+  }
+  
+  private def adjustOffsets(): Unit = {
+    for (i <- 0 until numOffsets) {
+      val off = offset(i)
+      val original = getAddr(off)
+      val corrected = adjustedOffset(off, isRelative(i))
+      fillAddr(off, corrected)
+    }
+  }
+    
+  private def adjustDeltas(): Int = {
+    val delta1 = new Array[Int](delta.length)
+    var lastDelta = 0
+    var i = 0
+    while (i < numOffsets) {
+      val corrected = adjustedOffset(offset(i), isRelative(i))
+      lastDelta += AddrWidth - TastyBuffer.natSize(corrected.index)
+      delta1(i) = lastDelta
+      i += 1
+    }
+    val saved = 
+      if (numOffsets == 0) 0
+      else delta1(numOffsets - 1) - delta(numOffsets - 1)
+    delta = delta1
+    saved
+  }
+    
+  private def compress(): Int = {
+    var lastDelta = 0
+    var start = 0
+    var i = 0
+    var wasted = 0
+    while (i < numOffsets) {
+      val next = offsets(i)
+      Array.copy(bytes, start, bytes, start - lastDelta, next - start)
+      start = next + delta(i) - lastDelta
+      val pastZeroes = skipZeroes(new Addr(next)).index
+      assert(pastZeroes >= start, s"something's wrong: eliminated non-zero")
+      wasted += (pastZeroes - start)
+      lastDelta = delta(i)
+      i += 1
+    }
+    length -= lastDelta
+    wasted
+  }
+  
+  override def assemble(): Unit = {
+    val origLength = length
+    computeDeltas()
+    adjustOffsets()
+    if (false) {
+      var saved = 0
+      do saved = adjustDeltas()
+      while (saved > 0 && length / saved < 100)
+    }
+    val wasted = compress()
+    println(s"original length: $origLength, compressed to: $length, wasted: $wasted")
+  }
+}
-- 
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