/**

* EdDSA-Java by str4d
*
* To the extent possible under law, the person who associated CC0 with
* EdDSA-Java has waived all copyright and related or neighboring rights
* to EdDSA-Java.
*
* You should have received a copy of the CC0 legalcode along with this
* work. If not, see <https://creativecommons.org/publicdomain/zero/1.0/>.
*
*/

package net.i2p.crypto.eddsa;

/**

* Basic utilities for EdDSA.
* Not for external use, not maintained as a public API.
*
* @author str4d
*
*/

public class Utils {

/**
 * Constant-time byte comparison.
 * @param b a byte
 * @param c a byte
 * @return 1 if b and c are equal, 0 otherwise.
 */
public static int equal(int b, int c) {
    int result = 0;
    int xor = b ^ c;
    for (int i = 0; i < 8; i++) {
        result |= xor >> i;
    }
    return (result ^ 0x01) & 0x01;
}

/**
 * Constant-time byte[] comparison.
 * @param b a byte[]
 * @param c a byte[]
 * @return 1 if b and c are equal, 0 otherwise.
 */
public static int equal(byte[] b, byte[] c) {
    int result = 0;
    for (int i = 0; i < 32; i++) {
        result |= b[i] ^ c[i];
    }

    return equal(result, 0);
}

/**
 * Constant-time determine if byte is negative.
 * @param b the byte to check.
 * @return 1 if the byte is negative, 0 otherwise.
 */
public static int negative(int b) {
    return (b >> 8) & 1;
}

/**
 * Get the i'th bit of a byte array.
 * @param h the byte array.
 * @param i the bit index.
 * @return 0 or 1, the value of the i'th bit in h
 */
public static int bit(byte[] h, int i) {
    return (h[i >> 3] >> (i & 7)) & 1;
}

/**
 * Converts a hex string to bytes.
 * @param s the hex string to be converted.
 * @return the byte[]
 */
public static byte[] hexToBytes(String s) {
    int len = s.length();
    byte[] data = new byte[len / 2];
    for (int i = 0; i < len; i += 2) {
        data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
                + Character.digit(s.charAt(i+1), 16));
    }
    return data;
}

/**
 * Converts bytes to a hex string.
 * @param raw the byte[] to be converted.
 * @return the hex representation as a string.
 */
public static String bytesToHex(byte[] raw) {
    if ( raw == null ) {
        return null;
    }
    final StringBuilder hex = new StringBuilder(2 * raw.length);
    for (final byte b : raw) {
        hex.append(Character.forDigit((b & 0xF0) >> 4, 16))
        .append(Character.forDigit((b & 0x0F), 16));
    }
    return hex.toString();
}

}