/* * SonarQube * Copyright (C) 2009-2017 SonarSource SA * mailto:info AT sonarsource DOT com * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 3 of the License, or (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public License * along with this program; if not, write to the Free Software Foundation, * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ package org.sonar.scanner.issue.tracking; /** * Compute hashes of block around each line */ public class RollingFileHashes { final int[] rollingHashes; private RollingFileHashes(int[] hashes) { this.rollingHashes = hashes; } public static RollingFileHashes create(FileHashes hashes, int halfBlockSize) { int size = hashes.length(); int[] rollingHashes = new int[size]; RollingHashCalculator hashCalulator = new RollingHashCalculator(halfBlockSize * 2 + 1); for (int i = 1; i <= Math.min(size, halfBlockSize + 1); i++) { hashCalulator.add(hashes.getHash(i).hashCode()); } for (int i = 1; i <= size; i++) { rollingHashes[i - 1] = hashCalulator.getHash(); if (i - halfBlockSize > 0) { hashCalulator.remove(hashes.getHash(i - halfBlockSize).hashCode()); } if (i + 1 + halfBlockSize <= size) { hashCalulator.add(hashes.getHash(i + 1 + halfBlockSize).hashCode()); } else { hashCalulator.add(0); } } return new RollingFileHashes(rollingHashes); } public int getHash(int line) { return rollingHashes[line - 1]; } private static class RollingHashCalculator { private static final int PRIME_BASE = 31; private final int power; private int hash; public RollingHashCalculator(int size) { int pow = 1; for (int i = 0; i < size - 1; i++) { pow = pow * PRIME_BASE; } this.power = pow; } public void add(int value) { hash = hash * PRIME_BASE + value; } public void remove(int value) { hash = hash - power * value; } public int getHash() { return hash; } } }