Provide direct access to table as an array instead of a String lookup to

avoid Java-level boundary checks.

Author: garydgregory

src/main/java/org/apache/commons/codec/digest/B64.java

@@ -19,10 +19,10 @@
 import java.util.concurrent.ThreadLocalRandom;
 
 /**
- * Base64 like method to convert binary bytes into ASCII chars.
- *
+ * Base64-like method to convert binary bytes into ASCII chars.
+ * <p>
  * TODO: Can Base64 be reused?
- *
+ * </p>
  * <p>
  * This class is immutable and thread-safe.
  * </p>
@@ -35,7 +35,12 @@ class B64 {
     /**
      * Table with characters for Base64 transformation.
      */
-    static final String B64T = "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
+    static final String B64T_STRING = "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
+
+    /**
+     * Table with characters for Base64 transformation.
+     */
+    static final char[] B64T_ARRAY = B64T_STRING.toCharArray();
 
     /**
      * Base64 like conversion of bytes to ASCII chars.
@@ -58,7 +63,7 @@ static void b64from24bit(final byte b2, final byte b1, final byte b0, final int
         // It's effectively a "for" loop but kept to resemble the original C code.
         int n = outLen;
         while (n-- > 0) {
-            buffer.append(B64T.charAt(w & 0x3f));
+            buffer.append(B64T_ARRAY[w & 0x3f]);
             w >>= 6;
         }
     }
@@ -76,7 +81,7 @@ static String getRandomSalt(final int num) {
         final StringBuilder saltString = new StringBuilder(num);
         final ThreadLocalRandom current = ThreadLocalRandom.current();
         for (int i = 1; i <= num; i++) {
-            saltString.append(B64T.charAt(current.nextInt(B64T.length())));
+            saltString.append(B64T_ARRAY[current.nextInt(B64T_ARRAY.length)]);
         }
         return saltString.toString();
     }

src/main/java/org/apache/commons/codec/digest/UnixCrypt.java

@@ -207,7 +207,7 @@ public static String crypt(final byte[] original, String salt) {
             final int numSaltChars = SALT_CHARS.length;
             salt = "" + SALT_CHARS[randomGenerator.nextInt(numSaltChars)] +
                     SALT_CHARS[randomGenerator.nextInt(numSaltChars)];
-        } else if (!salt.matches("^[" + B64.B64T + "]{2,}$")) {
+        } else if (!salt.matches("^[" + B64.B64T_STRING + "]{2,}$")) {
             throw new IllegalArgumentException("Invalid salt value: " + salt);
         }
 

src/test/java/org/apache/commons/codec/digest/B64Test.java

@@ -26,7 +26,7 @@ public class B64Test {
     @Test
     public void testB64T() {
         assertNotNull(new B64()); // for the 100% code coverage :)
-        assertEquals(64, B64.B64T.length());
+        assertEquals(64, B64.B64T_ARRAY.length);
     }
 
     @Test