Benchmarking two Scala atoi implementations: foldLeft vs random access

BenchmarkAtoi.scala

// <copyright file="BenchmarkAtoi.scala" company="http://www.javageneration.com">
// Copyright (c) Chaker Nakhli 2011 
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the
// License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by
// applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language
// governing permissions and limitations under the License. 
// </copyright>
// <author>Chaker Nakhli</author>
// <email>[email protected]</email>
// <date>2011/07/14</date>
package com.javageneration

object Atoi {
  def withRandomAccess(str: String, baze: Int): Int = {
	  def process(acc: Int, place: Int, str: String, index: Int): Int = 
	    if (index >= 0) process(acc + value(str.charAt(index)) * place, place * baze, str, index-1) else acc
	  process(0, 1, str, str.length - 1)
	}
	  
  def withFoldLeft(str: String, base: Int): Int = (0/:str) (_ * base + value(_))
	
  def value(c: Char): Int = {
    if (c == '+') 62
    else if (c == '/') 63
    else if (c < '0') throw new IndexOutOfBoundsException("c");
    else if (c < ':') c - '0';
    else if (c < 'A') throw new IndexOutOfBoundsException("c");
    else if (c < '[') c - 'A' + 10;
    else if (c < 'a') throw new IndexOutOfBoundsException("c");
    else if (c < '{') c - 'a' + 36;
    else throw new IndexOutOfBoundsException("c");
  }

  def symbol(i: Int): Char = {
    if (i < 0) throw new IndexOutOfBoundsException("i")
    else if (i < 10) ('0' + i).toChar
    else if (i < 36) ('A' + i - 10).toChar
    else if (i < 62) ('a' + i - 36).toChar
    else if (i == 62) '+'
    else if (i == 63) '/'
    else throw new IndexOutOfBoundsException("i");
  }
}

object Main {
  def main(args: Array[String]): Unit = {
    val MAX = 100000000
    benchmark(MAX, "1111111111111111111111111111111", 2)
    benchmark(MAX, "2147483647", 10)
    benchmark(MAX, "1/////", 64)
    benchmark(MAX, "0", 10)    
  }

  def benchmark(max: Int, str: String, baze: Int): Unit = {
    printf("** Input: Base=%d Str=\"%s\" - Atoi.withRandomAccess Output: %d - Atoi.withFoldLeft Output: %d **\n",
        baze, str, Atoi.withRandomAccess(str, baze), Atoi.withFoldLeft(str, baze))
    perf(max, "   Atoi.withRandomAccess :") { Atoi.withRandomAccess(str, baze) }
    perf(max, "   Atoi.withFoldLeft     :") { Atoi.withFoldLeft(str, baze) }
    println
  }

  def perf(max: Int, label: String)(action: => Unit): Unit = {
    var startedAt = System.currentTimeMillis()
    for (i <- 0 until max) action
    printf("%s %.0f ns\n", label, (System.currentTimeMillis() - startedAt) * 1000000.0 / max)
  }
}