src/jp/sfjp/armadillo/archive/cab/CabChecksum.java

   1 package jp.sfjp.armadillo.archive.cab;
   2
   3 import java.util.zip.*;
   4
   5 /**
   6  * Checksum for Cab file.
   7  * @see <a href="http://msdn.microsoft.com/en-us/library/bb267310.aspx">
   8  *      Microsoft Cabinet Format (http://msdn.microsoft.com/en-us/library/bb267310.aspx)</a>
   9  */
  10 public final class CabChecksum implements Checksum {
  11
  12     private final int seed;
  13
  14     private int value;
  15     private int p;
  16     private int tmp;
  17
  18     public CabChecksum() {
  19         this(0);
  20     }
  21
  22     public CabChecksum(int seed) {
  23         this.seed = seed;
  24         reset();
  25     }
  26
  27     @Override
  28     public void update(int b) {
  29         switch (++p % 4) {
  30             case 0:
  31                 tmp = b;
  32                 break;
  33             case 1:
  34                 tmp |= b << 8;
  35                 break;
  36             case 2:
  37                 tmp |= b << 16;
  38                 break;
  39             case 3:
  40                 tmp |= b << 24;
  41                 value ^= tmp;
  42                 tmp = 0;
  43                 break;
  44             default:
  45         }
  46     }
  47
  48     @Override
  49     public void update(byte[] b, int off, int len) {
  50         for (int i = off; i < len; i++)
  51             update(b[i] & 0xFF);
  52     }
  53
  54     @Override
  55     public long getValue() {
  56         final int tmpValue;
  57         final int mod = (p + 1) % 4;
  58         if (mod == 0)
  59             tmpValue = value;
  60         else {
  61             int x = 0;
  62             switch (mod) {
  63                 case 3:
  64                     x |= (tmp << 16) & 0xFF0000;
  65                     x |= tmp & 0x00FF00;
  66                     x |= (tmp >> 16) & 0x0000FF;
  67                     assert x == (x & 0xFFFFFF);
  68                     break;
  69                 case 2:
  70                     x |= (tmp << 8) & 0xFF00;
  71                     x |= (tmp >> 8) & 0x00FF;
  72                     assert x == (x & 0xFFFF);
  73                     break;
  74                 case 1:
  75                     x = tmp;
  76                     assert x == (x & 0xFF);
  77                     break;
  78                 default:
  79                     break;
  80             }
  81             tmpValue = value ^ x;
  82         }
  83         assert tmpValue == (tmpValue & 0xFFFFFFFF);
  84         return tmpValue;
  85     }
  86
  87     @Override
  88     public void reset() {
  89         value = seed;
  90         p = -1;
  91     }
  92
  93 }