implement java.util.zip.CRC32

classpath/java/util/zip/CRC32.java

@@ -0,0 +1,69 @@
+/* Copyright (c) 2011, Avian Contributors
+
+   Permission to use, copy, modify, and/or distribute this software
+   for any purpose with or without fee is hereby granted, provided
+   that the above copyright notice and this permission notice appear
+   in all copies.
+
+   There is NO WARRANTY for this software.  See license.txt for
+   details. */
+
+package java.util.zip;
+
+public class CRC32 {
+  private static final int Polynomial = 0x04C11DB7;
+  private static final int Width = 32;
+  private static final int Top = 1 << (Width - 1);
+  private static final int InitialRemainder = 0xFFFFFFFF;
+  private static final int ResultXor = 0xFFFFFFFF;
+
+  private static final int[] table = new int[256];
+
+  static {
+    for (int dividend = 0; dividend < 256; ++ dividend) {
+      int remainder = dividend << (Width - 8);
+      for (int bit = 8; bit > 0; --bit) {
+        remainder = ((remainder & Top) != 0)
+          ? (remainder << 1) ^ Polynomial
+          : (remainder << 1);
+      }
+      table[dividend] = remainder;
+    }
+  }
+
+  private int remainder = InitialRemainder;
+
+  public void reset() {
+    remainder = InitialRemainder;
+  }
+
+  public void update(int b) {
+    remainder = table[reflect(b, 8) ^ (remainder >>> (Width - 8))]
+      ^ (remainder << 8);
+  }
+
+  public void update(byte[] array, int offset, int length) {
+    for (int i = 0; i < length; ++i) {
+      update(array[offset + i] & 0xFF);
+    }
+  }
+
+  public void update(byte[] array) {
+    update(array, 0, array.length);
+  }
+
+  public long getValue() {
+    return reflect(remainder, Width) ^ ResultXor;
+  }
+
+  private static int reflect(int x, int n) {
+    int reflection = 0;
+    for (int i = 0; i < n; ++i) {
+      if ((x & 1) != 0) {
+        reflection |= (1 << ((n - 1) - i));
+      }
+      x = (x >>> 1);
+    }
+    return reflection;
+  }
+}