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/**
 * Copyright 2013-2016 Guoqiang Chen, Shanghai, China. All rights reserved.
 *
 *   Author: Guoqiang Chen
 *    Email: [email protected]
 *   WebURL: https://github.com/subchen
 *
 * 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 jetbrick.util.codec;

public final class HexUtils {
    private static final char[] DIGITS_LOWER = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };
    private static final char[] DIGITS_UPPER = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };

    public static byte[] decodeHex(char[] data) {
        int len = data.length;

        if ((len & 0x1) != 0) {
            throw new IllegalStateException("Odd number of characters.");
        }

        byte[] out = new byte[len >> 1];

        int i = 0;
        for (int j = 0; j < len; i++) {
            int f = toHexDigit(data[j], j) << 4;
            j++;
            f |= toHexDigit(data[j], j);
            j++;
            out[i] = ((byte) (f & 0xFF));
        }

        return out;
    }

    public static char[] encodeHex(byte[] data) {
        return encodeHex(data, true);
    }

    public static char[] encodeHex(byte[] data, boolean toLowerCase) {
        return encodeHex(data, toLowerCase ? DIGITS_LOWER : DIGITS_UPPER);
    }

    public static String encodeHexString(byte[] data) {
        return new String(encodeHex(data));
    }

    private static char[] encodeHex(byte[] data, char[] toDigits) {
        int l = data.length;
        char[] out = new char[l << 1];

        int i = 0;
        for (int j = 0; i < l; i++) {
            out[(j++)] = toDigits[((0xF0 & data[i]) >>> 4)];
            out[(j++)] = toDigits[(0xF & data[i])];
        }
        return out;
    }

    private static int toHexDigit(char ch, int index) {
        int digit = Character.digit(ch, 16);
        if (digit == -1) {
            throw new IllegalStateException("Illegal hexadecimal character " + ch + " at index " + index);
        }
        return digit;
    }
}