1 files changed, 141 insertions, 0 deletions
diff --git a/compiler/src/dotty/tools/dotc/core/tasty/TastyReader.scala b/compiler/src/dotty/tools/dotc/core/tasty/TastyReader.scala
new file mode 100644
index 000000000..e583c4793
--- /dev/null
+++ b/compiler/src/dotty/tools/dotc/core/tasty/TastyReader.scala
@@ -0,0 +1,141 @@
+package dotty.tools
+package dotc
+package core
+package tasty
+
+import TastyBuffer._
+import TastyName.NameRef
+import collection.mutable
+
+/** 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.
+ *
+ *  @param bytes    The array containing data
+ *  @param start    The position from which to read
+ *  @param end      The position one greater than the last byte to be read
+ *  @param base     The index referenced by the logical zero address Addr(0)
+ */
+class TastyReader(val bytes: Array[Byte], start: Int, end: Int, val base: Int = 0) {
+
+  def this(bytes: Array[Byte]) = this(bytes, 0, bytes.length)
+
+  private var bp: Int = start
+
+  def addr(idx: Int) = Addr(idx - base)
+  def index(addr: Addr) = addr.index + base
+
+  /** The address of the first byte to read, respectively byte that was read */
+  def startAddr: Addr = addr(start)
+
+  /** The address of the next byte to read */
+  def currentAddr: Addr = addr(bp)
+
+  /** the address one greater than the last brte to read */
+  def endAddr: Addr = addr(end)
+
+  /** Have all bytes been read? */
+  def isAtEnd: Boolean = bp == end
+
+  /** A new reader over the same array with the same address base, but with
+   *  specified start and end positions
+   */
+  def subReader(start: Addr, end: Addr): TastyReader =
+    new TastyReader(bytes, index(start), index(end), base)
+
+  /** Read a byte of data. */
+  def readByte(): Int = {
+    val result = bytes(bp) & 0xff
+    bp += 1
+    result
+  }
+
+  /** Returns the next byte of data as a natural number without advancing the read position */
+  def nextByte: Int = bytes(bp) & 0xff
+
+  /** Read the next `n` bytes of `data`. */
+  def readBytes(n: Int): Array[Byte] = {
+    val result = new Array[Byte](n)
+    Array.copy(bytes, bp, result, 0, n)
+    bp += n
+    result
+  }
+
+  /** Read a natural number fitting in an Int in big endian format, base 128.
+   *  All but the last digits have bit 0x80 set.
+   */
+  def readNat(): Int = readLongNat.toInt
+
+  /** Read an integer number in 2's complement big endian format, base 128.
+   *  All but the last digits have bit 0x80 set.
+   */
+  def readInt(): Int = readLongInt.toInt
+
+  /** Read a natural number fitting in a Long in big endian format, base 128.
+   *  All but the last digits have bit 0x80 set.
+   */
+  def readLongNat(): Long = {
+    var b = 0L
+    var x = 0L
+    do {
+      b = bytes(bp)
+      x = (x << 7) | (b & 0x7f)
+      bp += 1
+    } while ((b & 0x80) == 0)
+    x
+  }
+
+  /** Read a long integer number in 2's complement big endian format, base 128. */
+  def readLongInt(): Long = {
+    var b = bytes(bp)
+    var x: Long = (b << 1).toByte >> 1 // sign extend with bit 6.
+    bp += 1
+    while ((b & 0x80) == 0) {
+      b = bytes(bp)
+      x = (x << 7) | (b & 0x7f)
+      bp += 1
+    }
+    x
+  }
+
+  /** Read an uncompressed Long stored in 8 bytes in big endian format */
+  def readUncompressedLong(): Long = {
+    var x: Long = 0
+    for (i <- 0 to 7)
+      x = (x << 8) | (readByte() & 0xff)
+    x
+  }
+
+  /** Read a natural number and return as a NameRef */
+  def readNameRef() = NameRef(readNat())
+
+  /** Read a natural number and return as an address */
+  def readAddr() = Addr(readNat())
+
+  /** Read a length number and return the absolute end address implied by it,
+   *  given as <address following length field> + <length-value-read>.
+   */
+  def readEnd(): Addr = addr(readNat() + bp)
+
+  /** Set read position to the one pointed to by `addr` */
+  def goto(addr: Addr): Unit =
+    bp = index(addr)
+
+  /** Perform `op` until `end` address is reached and collect results in a list. */
+  def until[T](end: Addr)(op: => T): List[T] = {
+    val buf = new mutable.ListBuffer[T]
+    while (bp < index(end)) buf += op
+    assert(bp == index(end))
+    buf.toList
+  }
+
+  /** If before given `end` address, the result of `op`, otherwise `default` */
+  def ifBefore[T](end: Addr)(op: => T, default: T): T =
+    if (bp < index(end)) op else default
+
+  /** Perform `op` while cindition `cond` holds and collect results in a list. */
+  def collectWhile[T](cond: => Boolean)(op: => T): List[T] = {
+    val buf = new mutable.ListBuffer[T]
+    while (cond) buf += op
+    buf.toList
+  }
+}