Add base36 implementation

Author: ianopolous

src/main/java/io/ipfs/multibase/Base36.java

@@ -0,0 +1,42 @@
+package io.ipfs.multibase;
+
+import java.math.*;
+
+public class Base36 {
+
+    public static byte[] decode(String in) {
+        byte[] withoutLeadingZeroes = new BigInteger(in, 36).toByteArray();
+        int zeroPrefixLength = zeroPrefixLength(in);
+        byte[] res = new byte[zeroPrefixLength + withoutLeadingZeroes.length];
+        System.arraycopy(withoutLeadingZeroes, 0, res, zeroPrefixLength, withoutLeadingZeroes.length);
+        return res;
+    }
+
+    public static String encode(byte[] in) {
+        String withoutLeadingZeroes = new BigInteger(1, in).toString(36);
+        int zeroPrefixLength = zeroPrefixLength(in);
+        StringBuilder b = new StringBuilder();
+        for (int i=0; i < zeroPrefixLength; i++)
+            b.append("0");
+        b.append(withoutLeadingZeroes);
+        return b.toString();
+    }
+
+    private static int zeroPrefixLength(byte[] bytes) {
+        for (int i = 0; i < bytes.length; i++) {
+            if (bytes[i] != 0) {
+                return i;
+            }
+        }
+        return bytes.length;
+    }
+
+    private static int zeroPrefixLength(String in) {
+        for (int i = 0; i < in.length(); i++) {
+            if (in.charAt(i) != '0') {
+                return i;
+            }
+        }
+        return in.length();
+    }
+}

src/main/java/io/ipfs/multibase/Multibase.java

@@ -17,6 +17,7 @@ public enum Base {
         Base32Upper('B'),
         Base32Hex('v'),
         Base32HexUpper('V'),
+        Base36('k'),
         Base58Flickr('Z'),
         Base58BTC('z'),
         Base64('m'),
@@ -55,6 +56,8 @@ public static String encode(Base b, byte[] data) {
                 return b.prefix + new String(new Base32(true).encode(data)).toLowerCase().replaceAll("=", "");
             case Base32HexUpper:
                 return b.prefix + new String(new Base32(true).encode(data)).replaceAll("=", "");
+            case Base36:
+                return b.prefix + Base36.encode(data);
             case Base64:
                 return b.prefix + Base64.encodeBase64String(data).replaceAll("=", "");
             case Base64Pad:
@@ -84,6 +87,8 @@ public static byte[] decode(String data) {
                 return new Base32(true).decode(rest);
             case Base32HexUpper:
                 return new Base32(true).decode(rest.toLowerCase());
+            case Base36:
+                return Base36.decode(rest);
             case Base64Pad:
             case Base64:
                 return Base64.decodeBase64(rest);

src/test/java/io/ipfs/multibase/MultibaseTest.java

@@ -48,6 +48,8 @@ public static Collection<Object[]> data() {
                 {Multibase.Base.Base32Upper, hexToBytes("446563656e7472616c697a652065766572797468696e67212121"), "BIRSWGZLOORZGC3DJPJSSAZLWMVZHS5DINFXGOIJBEE"},
                 {Multibase.Base.Base32Hex, hexToBytes("446563656e7472616c697a652065766572797468696e67212121"), "v8him6pbeehp62r39f9ii0pbmclp7it38d5n6e89144"},
                 {Multibase.Base.Base32HexUpper, hexToBytes("446563656e7472616c697a652065766572797468696e67212121"), "V8HIM6PBEEHP62R39F9II0PBMCLP7IT38D5N6E89144"},
+                {Multibase.Base.Base36, hexToBytes("446563656e7472616c697a652065766572797468696e67212121"), "km552ng4dabi4neu1oo8l4i5mndwmpc3mkukwtxy9"},
+                {Multibase.Base.Base36, hexToBytes("00446563656e7472616c697a652065766572797468696e67212121"), "k0m552ng4dabi4neu1oo8l4i5mndwmpc3mkukwtxy9"},
                 {Multibase.Base.Base58BTC, hexToBytes("446563656e7472616c697a652065766572797468696e67212121"), "z36UQrhJq9fNDS7DiAHM9YXqDHMPfr4EMArvt"},
                 {Multibase.Base.Base64, hexToBytes("446563656e7472616c697a652065766572797468696e67212121"), "mRGVjZW50cmFsaXplIGV2ZXJ5dGhpbmchISE"},
                 {Multibase.Base.Base64Pad, hexToBytes("446563656e7472616c697a652065766572797468696e67212121"), "MRGVjZW50cmFsaXplIGV2ZXJ5dGhpbmchISE="},