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 }