1 /*
   2  * Copyright (c) 2012, 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  */
  23 package vm.compiler.coverage.parentheses.share.generation;
  24 
  25 import vm.compiler.coverage.parentheses.share.Instruction;
  26 import vm.compiler.coverage.parentheses.share.InstructionSequence;
  27 
  28 import java.util.ArrayList;
  29 import java.util.List;
  30 import java.util.Random;
  31 
  32 /**
  33  * Generates random but correct list of JVM instructions
  34  */
  35 public class RandomInstructionsGenerator {
  36     private static Random random = new Random();
  37 
  38     private static <E> E choseRandomElement(List<E> list) {
  39         return list.get(random.nextInt(list.size()));
  40     }
  41 
  42     private int maxStackDepth;
  43 
  44     public RandomInstructionsGenerator(int maxStackDepth) {
  45         this.maxStackDepth = maxStackDepth;
  46     }
  47 
  48     public InstructionSequence generate() {
  49         List<Instruction> instructions = new ArrayList<Instruction>();
  50 
  51         //this head with constants is necessary to avoid stack underflow
  52         instructions.add(Instruction.ICONST_1);
  53         instructions.add(Instruction.ICONST_2);
  54 
  55 
  56         String parenthesis = ParenthesesGenerator.generate(maxStackDepth - 2);
  57 
  58         for (char c : parenthesis.toCharArray()) {
  59             if (c == '(') {
  60                 //+1: add op that increase stack
  61                 instructions.add(choseRandomElement(Instruction.stackUp));
  62             } else {
  63                 //-1
  64                 instructions.add(choseRandomElement(Instruction.stackDown));
  65             }
  66 
  67             //+0: add element that doesn't change stack
  68             if (random.nextBoolean()) {
  69                 instructions.add(choseRandomElement(Instruction.neutral));
  70             }
  71 
  72         }
  73         return new InstructionSequence(instructions, maxStackDepth);
  74     }
  75 }