Match slot ID's to keystore aliases

app/src/main/java/me/impy/aegis/util/Hex.java

@@ -0,0 +1,46 @@
+package me.impy.aegis.util;
+
+// The hexadecimal utility functions in this file were taken and modified from: http://www.docjar.com/html/api/com/sun/xml/internal/bind/DatatypeConverterImpl.java.html
+// It is licensed under GPLv2 with a classpath exception.
+public class Hex {
+    private Hex() {
+    }
+
+    private static int hexToBin(char ch) {
+        if ('0' <= ch && ch <= '9') return ch - '0';
+        if ('A' <= ch && ch <= 'F') return ch - 'A' + 10;
+        if ('a' <= ch && ch <= 'f') return ch - 'a' + 10;
+        return -1;
+    }
+
+    private static final char[] hexCode = "0123456789abcdef".toCharArray();
+
+    public static byte[] toBytes(String s) {
+        final int len = s.length();
+
+        if (len % 2 != 0)
+            throw new IllegalArgumentException("hexBinary needs to be even-length: " + s);
+
+        byte[] out = new byte[len / 2];
+
+        for (int i = 0; i < len; i += 2) {
+            int h = hexToBin(s.charAt(i));
+            int l = hexToBin(s.charAt(i + 1));
+            if (h == -1 || l == -1)
+                throw new IllegalArgumentException("contains illegal character for hexBinary: " + s);
+
+            out[i / 2] = (byte) (h * 16 + l);
+        }
+
+        return out;
+    }
+
+    public static String toString(byte[] data) {
+        StringBuilder r = new StringBuilder(data.length * 2);
+        for (byte b : data) {
+            r.append(hexCode[(b >> 4) & 0xF]);
+            r.append(hexCode[(b & 0xF)]);
+        }
+        return r.toString();
+    }
+}