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/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * 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 libcore.util;

/**
 * Converts integral types to strings. This class is public but hidden so that it can also be
 * used by java.util.Formatter to speed up %d. This class is in java.lang so that it can take
 * advantage of the package-private String constructor.
 *
 * The most important methods are appendInt/appendLong and intToString(int)/longToString(int).
 * The former are used in the implementation of StringBuilder, StringBuffer, and Formatter, while
 * the latter are used by Integer.toString and Long.toString.
 *
 * The append methods take AbstractStringBuilder rather than Appendable because the latter requires
 * CharSequences, while we only have raw char[]s. Since much of the savings come from not creating
 * any garbage, we can't afford temporary CharSequence instances.
 *
 * One day the performance advantage of the binary/hex/octal specializations will be small enough
 * that we can lose the duplication, but until then this class offers the full set.
 *
 * @hide
 */
public final class IntegralToString {
    /**
     * The digits for every supported radix.
     */
    private static final char[] DIGITS = {
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
        'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
        'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
        'u', 'v', 'w', 'x', 'y', 'z'
    };

    private static final char[] UPPER_CASE_DIGITS = {
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
        'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
        'U', 'V', 'W', 'X', 'Y', 'Z'
    };

    private IntegralToString() {
    }

    public static String bytesToHexString(byte[] bytes, boolean upperCase) {
        char[] digits = upperCase ? UPPER_CASE_DIGITS : DIGITS;
        char[] buf = new char[bytes.length * 2];
        int c = 0;
        for (byte b : bytes) {
            buf[c++] = digits[(b >> 4) & 0xf];
            buf[c++] = digits[b & 0xf];
        }
        return new String(buf);
    }
}