Scala example source code file (ConstantFolder.scala)

This example Scala source code file (ConstantFolder.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

arithmeticexception, booleantag, constant, constanttype, doubletag, floattag, inttag, longtag, name, tree

The ConstantFolder.scala Scala example source code

/* NSC -- new Scala compiler
 * Copyright 2005-2013 LAMP/EPFL
 * @author  Martin Odersky
 */

package scala
package tools.nsc
package typechecker

import java.lang.ArithmeticException

/** This class ...
 *
 *  @author Martin Odersky
 *  @version 1.0
 */
abstract class ConstantFolder {

  val global: Global
  import global._

  /** If tree is a constant operation, replace with result. */
  def apply(tree: Tree): Tree = fold(tree, tree match {
    case Apply(Select(Literal(x), op), List(Literal(y))) => foldBinop(op, x, y)
    case Select(Literal(x), op) => foldUnop(op, x)
    case _ => null
  })

  /** If tree is a constant value that can be converted to type `pt`, perform
   *  the conversion.
   */
  def apply(tree: Tree, pt: Type): Tree = fold(apply(tree), tree.tpe match {
    case ConstantType(x) => x convertTo pt
    case _ => null
  })

  private def fold(tree: Tree, compX: => Constant): Tree =
    try {
      val x = compX
      if ((x ne null) && x.tag != UnitTag) tree setType ConstantType(x)
      else tree
    } catch {
      case _: ArithmeticException => tree   // the code will crash at runtime,
                                           // but that is better than the
                                           // compiler itself crashing
    }

  private def foldUnop(op: Name, x: Constant): Constant = (op, x.tag) match {
    case (nme.UNARY_!, BooleanTag) => Constant(!x.booleanValue)

    case (nme.UNARY_~ , IntTag    ) => Constant(~x.intValue)
    case (nme.UNARY_~ , LongTag   ) => Constant(~x.longValue)

    case (nme.UNARY_+ , IntTag    ) => Constant(+x.intValue)
    case (nme.UNARY_+ , LongTag   ) => Constant(+x.longValue)
    case (nme.UNARY_+ , FloatTag  ) => Constant(+x.floatValue)
    case (nme.UNARY_+ , DoubleTag ) => Constant(+x.doubleValue)

    case (nme.UNARY_- , IntTag    ) => Constant(-x.intValue)
    case (nme.UNARY_- , LongTag   ) => Constant(-x.longValue)
    case (nme.UNARY_- , FloatTag  ) => Constant(-x.floatValue)
    case (nme.UNARY_- , DoubleTag ) => Constant(-x.doubleValue)

    case _ => null
  }

  /** These are local helpers to keep foldBinop from overly taxing the
   *  optimizer.
   */
  private def foldBooleanOp(op: Name, x: Constant, y: Constant): Constant = op match {
    case nme.ZOR  => Constant(x.booleanValue | y.booleanValue)
    case nme.OR   => Constant(x.booleanValue | y.booleanValue)
    case nme.XOR  => Constant(x.booleanValue ^ y.booleanValue)
    case nme.ZAND => Constant(x.booleanValue & y.booleanValue)
    case nme.AND  => Constant(x.booleanValue & y.booleanValue)
    case nme.EQ   => Constant(x.booleanValue == y.booleanValue)
    case nme.NE   => Constant(x.booleanValue != y.booleanValue)
    case _ => null
  }
  private def foldSubrangeOp(op: Name, x: Constant, y: Constant): Constant = op match {
    case nme.OR  => Constant(x.intValue | y.intValue)
    case nme.XOR => Constant(x.intValue ^ y.intValue)
    case nme.AND => Constant(x.intValue & y.intValue)
    case nme.LSL => Constant(x.intValue << y.intValue)
    case nme.LSR => Constant(x.intValue >>> y.intValue)
    case nme.ASR => Constant(x.intValue >> y.intValue)
    case nme.EQ  => Constant(x.intValue == y.intValue)
    case nme.NE  => Constant(x.intValue != y.intValue)
    case nme.LT  => Constant(x.intValue < y.intValue)
    case nme.GT  => Constant(x.intValue > y.intValue)
    case nme.LE  => Constant(x.intValue <= y.intValue)
    case nme.GE  => Constant(x.intValue >= y.intValue)
    case nme.ADD => Constant(x.intValue + y.intValue)
    case nme.SUB => Constant(x.intValue - y.intValue)
    case nme.MUL => Constant(x.intValue * y.intValue)
    case nme.DIV => Constant(x.intValue / y.intValue)
    case nme.MOD => Constant(x.intValue % y.intValue)
    case _ => null
  }
  private def foldLongOp(op: Name, x: Constant, y: Constant): Constant = op match {
    case nme.OR  => Constant(x.longValue | y.longValue)
    case nme.XOR => Constant(x.longValue ^ y.longValue)
    case nme.AND => Constant(x.longValue & y.longValue)
    case nme.LSL => Constant(x.longValue << y.longValue)
    case nme.LSR => Constant(x.longValue >>> y.longValue)
    case nme.ASR => Constant(x.longValue >> y.longValue)
    case nme.EQ  => Constant(x.longValue == y.longValue)
    case nme.NE  => Constant(x.longValue != y.longValue)
    case nme.LT  => Constant(x.longValue < y.longValue)
    case nme.GT  => Constant(x.longValue > y.longValue)
    case nme.LE  => Constant(x.longValue <= y.longValue)
    case nme.GE  => Constant(x.longValue >= y.longValue)
    case nme.ADD => Constant(x.longValue + y.longValue)
    case nme.SUB => Constant(x.longValue - y.longValue)
    case nme.MUL => Constant(x.longValue * y.longValue)
    case nme.DIV => Constant(x.longValue / y.longValue)
    case nme.MOD => Constant(x.longValue % y.longValue)
    case _ => null
  }
  private def foldFloatOp(op: Name, x: Constant, y: Constant): Constant = op match {
    case nme.EQ  => Constant(x.floatValue == y.floatValue)
    case nme.NE  => Constant(x.floatValue != y.floatValue)
    case nme.LT  => Constant(x.floatValue < y.floatValue)
    case nme.GT  => Constant(x.floatValue > y.floatValue)
    case nme.LE  => Constant(x.floatValue <= y.floatValue)
    case nme.GE  => Constant(x.floatValue >= y.floatValue)
    case nme.ADD => Constant(x.floatValue + y.floatValue)
    case nme.SUB => Constant(x.floatValue - y.floatValue)
    case nme.MUL => Constant(x.floatValue * y.floatValue)
    case nme.DIV => Constant(x.floatValue / y.floatValue)
    case nme.MOD => Constant(x.floatValue % y.floatValue)
    case _ => null
  }
  private def foldDoubleOp(op: Name, x: Constant, y: Constant): Constant = op match {
    case nme.EQ  => Constant(x.doubleValue == y.doubleValue)
    case nme.NE  => Constant(x.doubleValue != y.doubleValue)
    case nme.LT  => Constant(x.doubleValue < y.doubleValue)
    case nme.GT  => Constant(x.doubleValue > y.doubleValue)
    case nme.LE  => Constant(x.doubleValue <= y.doubleValue)
    case nme.GE  => Constant(x.doubleValue >= y.doubleValue)
    case nme.ADD => Constant(x.doubleValue + y.doubleValue)
    case nme.SUB => Constant(x.doubleValue - y.doubleValue)
    case nme.MUL => Constant(x.doubleValue * y.doubleValue)
    case nme.DIV => Constant(x.doubleValue / y.doubleValue)
    case nme.MOD => Constant(x.doubleValue % y.doubleValue)
    case _ => null
  }

  private def foldBinop(op: Name, x: Constant, y: Constant): Constant = {
    val optag =
      if (x.tag == y.tag) x.tag
      else if (x.isNumeric && y.isNumeric) math.max(x.tag, y.tag)
      else NoTag

    try optag match {
      case BooleanTag                               => foldBooleanOp(op, x, y)
      case ByteTag | ShortTag | CharTag | IntTag    => foldSubrangeOp(op, x, y)
      case LongTag                                  => foldLongOp(op, x, y)
      case FloatTag                                 => foldFloatOp(op, x, y)
      case DoubleTag                                => foldDoubleOp(op, x, y)
      case StringTag if op == nme.ADD               => Constant(x.stringValue + y.stringValue)
      case _                                        => null
    }
    catch {
      case ex: ArithmeticException => null
    }
  }
}