1 files changed, 188 insertions, 0 deletions
diff --git a/compiler/src/dotty/tools/dotc/core/tasty/TastyBuffer.scala b/compiler/src/dotty/tools/dotc/core/tasty/TastyBuffer.scala
new file mode 100644
index 000000000..13bc95028
--- /dev/null
+++ b/compiler/src/dotty/tools/dotc/core/tasty/TastyBuffer.scala
@@ -0,0 +1,188 @@
+package dotty.tools
+package dotc
+package core
+package tasty
+
+import util.Util.dble
+
+object TastyBuffer {
+
+  /** The number of digits of the natural number `nat`, written in base 128 format. */
+  def natSize(nat: Int): Int =
+    if (nat < 128) 1 else natSize(nat >>> 7) + 1
+
+  /** An address pointing to an index in a Tasty buffer's byte array */
+  case class Addr(index: Int) extends AnyVal {
+    def - (delta: Int): Addr = Addr(this.index - delta)
+    def + (delta: Int): Addr = Addr(this.index + delta)
+
+    def relativeTo(base: Addr): Addr = this - base.index - AddrWidth
+  }
+
+  val NoAddr = Addr(-1)
+
+  /** The maximal number of address bytes.
+   *  Since addresses are written as base-128 natural numbers,
+   *  the value of 4 gives a maximal array size of 256M.
+   */
+  final val AddrWidth = 4
+}
+import TastyBuffer._
+
+/** A byte array buffer that can be filled with bytes or natural numbers in TASTY format,
+ *  and that supports reading and patching addresses represented as natural numbers.
+ */
+class TastyBuffer(initialSize: Int) {
+
+  /** The current byte array, will be expanded as needed */
+  var bytes = new Array[Byte](initialSize)
+
+  /** The number of bytes written */
+  var length = 0
+
+  // -- Output routines --------------------------------------------
+
+  /** Write a byte of data. */
+  def writeByte(b: Int): Unit = {
+    if (length >= bytes.length)
+      bytes = dble(bytes)
+    bytes(length) = b.toByte
+    length += 1
+  }
+
+  /** Write the first `n` bytes of `data`. */
+  def writeBytes(data: Array[Byte], n: Int): Unit = {
+    while (bytes.length < length + n) bytes = dble(bytes)
+    Array.copy(data, 0, bytes, length, n)
+    length += n
+  }
+
+  /** Write a natural number in big endian format, base 128.
+   *  All but the last digits have bit 0x80 set.
+   */
+  def writeNat(x: Int): Unit =
+    writeLongNat(x.toLong & 0x00000000FFFFFFFFL)
+
+  /** Write a natural number in 2's complement big endian format, base 128.
+   *  All but the last digits have bit 0x80 set.
+   */
+  def writeInt(x: Int): Unit =
+    writeLongInt(x)
+
+  /**
+   * Like writeNat, but for longs. Note that the
+   * binary representation of LongNat is identical to Nat
+   * if the long value is in the range Int.MIN_VALUE to
+   * Int.MAX_VALUE.
+   */
+  def writeLongNat(x: Long): Unit = {
+    def writePrefix(x: Long): Unit = {
+      val y = x >>> 7
+      if (y != 0L) writePrefix(y)
+      writeByte((x & 0x7f).toInt)
+    }
+    val y = x >>> 7
+    if (y != 0L) writePrefix(y)
+    writeByte(((x & 0x7f) | 0x80).toInt)
+  }
+
+  /** Like writeInt, but for longs */
+  def writeLongInt(x: Long): Unit = {
+    def writePrefix(x: Long): Unit = {
+      val y = x >> 7
+      if (y != 0L - ((x >> 6) & 1)) writePrefix(y)
+      writeByte((x & 0x7f).toInt)
+    }
+    val y = x >> 7
+    if (y != 0L - ((x >> 6) & 1)) writePrefix(y)
+    writeByte(((x & 0x7f) | 0x80).toInt)
+  }
+
+  /** Write an uncompressed Long stored in 8 bytes in big endian format */
+  def writeUncompressedLong(x: Long): Unit = {
+    var y = x
+    val bytes = new Array[Byte](8)
+    for (i <- 7 to 0 by -1) {
+      bytes(i) = (y & 0xff).toByte
+      y = y >>> 8
+    }
+    writeBytes(bytes, 8)
+  }
+
+  // -- Address handling --------------------------------------------
+
+  /** Write natural number `x` right-adjusted in a field of `width` bytes
+   *  starting with address `at`.
+   */
+  def putNat(at: Addr, x: Int, width: Int): Unit = {
+    var y = x
+    var w = width
+    if(at.index + w >= bytes.length)
+      bytes = dble(bytes)
+    var digit = y & 0x7f | 0x80
+    while (w > 0) {
+      w -= 1
+      bytes(at.index + w) = digit.toByte
+      y >>>= 7
+      digit = y & 0x7f
+    }
+    assert(y == 0, s"number $x too large to fit in $width bytes")
+  }
+
+  /** The byte at given address */
+  def getByte(at: Addr): Int = bytes(at.index)
+
+  /** The natural number at address `at` */
+  def getNat(at: Addr): Int = getLongNat(at).toInt
+
+  /** The long natural number at address `at` */
+  def getLongNat(at: Addr): Long = {
+    var b = 0L
+    var x = 0L
+    var idx = at.index
+    do {
+      b = bytes(idx)
+      x = (x << 7) | (b & 0x7f)
+      idx += 1
+    } while ((b & 0x80) == 0)
+    x
+  }
+
+  /** The address (represented as a natural number) at address `at` */
+  def getAddr(at: Addr) = Addr(getNat(at))
+
+  /** The smallest address equal to or following `at` which points to a non-zero byte */
+  final def skipZeroes(at: Addr): Addr =
+    if (getByte(at) != 0) at else skipZeroes(at + 1)
+
+  /** The address after the natural number found at address `at`. */
+  final def skipNat(at: Addr): Addr = {
+    val next = at + 1
+    if ((getByte(at) & 0x80) != 0) next else skipNat(next)
+  }
+
+  /** The address referring to the end of data written so far */
+  def currentAddr: Addr = Addr(length)
+
+  /** Reserve `AddrWidth` bytes to write an address into */
+  def reserveAddr(): Addr = {
+    val result = currentAddr
+    length += AddrWidth
+    result
+  }
+
+  /** Fill reserved space at address `at` with address `target` */
+  def fillAddr(at: Addr, target: Addr) =
+    putNat(at, target.index, AddrWidth)
+
+  /** Write address without leading zeroes */
+  def writeAddr(addr: Addr): Unit = writeNat(addr.index)
+
+  // -- Finalization --------------------------------------------
+
+  /** Hook to be overridden in subclasses.
+   *  Perform all actions necessary to assemble the final byte array.
+   *  After `assemble` no more output actions to this buffer are permitted.
+   */
+  def assemble(): Unit = ()
+}