annotate src/com/tmate/hgkit/ll/Nodeid.java @ 34:51bc56c0addd

Static Nodeid creation methods to reuse NULL id
author Artem Tikhomirov <tikhomirov.artem@gmail.com>
date Thu, 13 Jan 2011 04:03:13 +0100
parents 346b66add79d
children 858d1b2458cb
rev   line source
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1 /*
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2 * Copyright (c) 2010, 2011 Artem Tikhomirov
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3 */
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4 package com.tmate.hgkit.ll;
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6 import static com.tmate.hgkit.ll.DigestHelper.toHexString;
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8 import java.util.Arrays;
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12 /**
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13 * Whether to store fixed size array (20 bytes) - ease of manipulation (e.g. hashcode/equals), or
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14 * memory effective - reuse supplied array, keep significant bits only?
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15 * Fixed size array looks most appealing to me now - I doubt one can save any significant amount of memory.
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16 * There'd always 20 non-zero bytes, the difference is only for any extra bytes one may pass to constructor
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17 * @author artem
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18 *
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19 */
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20 public final class Nodeid {
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22 public static final Nodeid NULL = new Nodeid(new byte[20], false);
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23 private final byte[] binaryData;
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24
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25 /**
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26 * @param binaryRepresentation - byte[20], kept by reference
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27 * @param shallClone - true if array is subject to future modification and shall be copied, not referenced
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28 */
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29 public Nodeid(byte[] binaryRepresentation, boolean shallClone) {
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30 // 5 int fields => 32 bytes
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31 // byte[20] => 48 bytes
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32 if (binaryRepresentation == null || binaryRepresentation.length != 20) {
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33 throw new IllegalArgumentException();
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34 }
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35 this.binaryData = shallClone ? binaryRepresentation.clone() : binaryRepresentation;
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36 }
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37
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38 @Override
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39 public int hashCode() {
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40 // TODO consider own impl, especially if byte[] get replaced with 5 ints
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41 return Arrays.hashCode(binaryData);
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42 }
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43
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44 @Override
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45 public boolean equals(Object o) {
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46 if (o instanceof Nodeid) {
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47 return Arrays.equals(this.binaryData, ((Nodeid) o).binaryData);
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48 }
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49 return false;
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50 }
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51
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52 public boolean equalsTo(byte[] buf) {
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53 return Arrays.equals(this.binaryData, buf);
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54 }
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55
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56 @Override
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57 public String toString() {
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58 // XXX may want to output just single 0 for the NULL id?
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59 return toHexString(binaryData, 0, binaryData.length);
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60 }
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61
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62 public String shortNotation() {
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63 return toHexString(binaryData, 0, 6);
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64 }
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65
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66 public boolean isNull() {
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67 if (this == NULL) {
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68 return true;
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69 }
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70 for (int i = 0; i < 20; i++) {
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71 if (this.binaryData[i] != 0) {
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72 return false;
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73 }
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74 }
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75 return true;
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76 }
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77
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78 // primary difference with cons is handling of NULL id (this method returns constant)
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79 // always makes a copy of an array passed
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80 public static Nodeid fromBinary(byte[] binaryRepresentation, int offset) {
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81 if (binaryRepresentation == null || binaryRepresentation.length - offset < 20) {
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82 throw new IllegalArgumentException();
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83 }
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84 int i = 0;
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85 while (i < 20 && binaryRepresentation[offset+i] == 0) i++;
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86 if (i == 20) {
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87 return NULL;
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88 }
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89 if (offset == 0 && binaryRepresentation.length == 20) {
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90 return new Nodeid(binaryRepresentation, true);
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91 }
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92 byte[] b = new byte[20]; // create new instance if no other reasonable guesses possible
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93 System.arraycopy(binaryRepresentation, offset, b, 0, 20);
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94 return new Nodeid(b, false);
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95 }
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96
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97 // binascii.unhexlify()
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98 public static Nodeid fromAscii(byte[] asciiRepresentation, int offset, int length) {
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99 if (length != 40) {
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100 throw new IllegalArgumentException();
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101 }
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102 byte[] data = new byte[20];
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103 boolean zeroBytes = true;
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104 for (int i = 0, j = offset; i < data.length; i++) {
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105 int hiNibble = Character.digit(asciiRepresentation[j++], 16);
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106 int lowNibble = Character.digit(asciiRepresentation[j++], 16);
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107 byte b = (byte) (((hiNibble << 4) | lowNibble) & 0xFF);
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108 data[i] = b;
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109 zeroBytes = zeroBytes && b == 0;
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110 }
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111 if (zeroBytes) {
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112 return NULL;
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113 }
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114 return new Nodeid(data, false);
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115 }
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116 }