Add support for CRC32

Author: Horcrux7

src/java/util/zip/ReplacementForCRC32.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2019 Volker Berlin (i-net software)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package java.util.zip;
+
+import de.inetsoftware.jwebassembly.api.annotation.Replace;
+
+/**
+ * Replacement methods for the class java.util.zip.CRC32
+ * 
+ * @author Volker Berlin
+ */
+class ReplacementForCRC32 {
+
+    /**
+     * Replacement for CRC32.update(int, int)
+     */
+    @Replace( "java/util/zip/CRC32.update(II)I" )
+    static int update( int crc, int b ) {
+        return 0; // for Java compiler
+    }
+
+    /**
+     * Replacement for CRC32.updateBytes(int, byte[], int, int)
+     */
+    @Replace( "java/util/zip/CRC32.updateBytes(I[BII)I" )
+    static int updateBytes( int crc, byte[] data, int off, int len ) {
+        int[] crcTable = cachedCrcTable;
+        if( crcTable == null ) {
+            crcTable = makeCRCTable();
+        }
+
+        crc ^= -1;
+        for( ; off < len; off++ ) {
+            crc = (crc >>> 8) ^ crcTable[(crc ^ data[off]) & 0xFF];
+        }
+
+        return crc ^ -1;
+    }
+
+    /**
+     * Create table for a byte-wise 32-bit CRC calculation on the polynomial:
+     * x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1.
+     * 
+     * @return the table
+     */
+    private static int[] makeCRCTable() {
+        int[] crcTable = cachedCrcTable;
+        if( crcTable != null ) {
+            return crcTable;
+        }
+        crcTable = new int[256];
+        for( int n = 0; n < 256; n++ ) {
+            int c = n;
+            for( int k = 0; k < 8; k++ ) {
+                c = ((c & 1) == 1 ? (0xEDB88320 ^ (c >>> 1)) : (c >>> 1));
+            }
+            crcTable[n] = c;
+        }
+        return cachedCrcTable = crcTable;
+    }
+
+    private static int[] cachedCrcTable;
+}