Base64

public class Base64Utils {
  private Base64Utils() {
  }

  public static byte[] decode(String in) {
    // Ignore trailing '=' padding and whitespace from the input.
    int limit = in.length();
    for (; limit > 0; limit--) {
      char c = in.charAt(limit - 1);
      if (c != '=' && c != '\n' && c != '\r' && c != ' ' && c != '\t') {
        break;
      }
    }

    // If the input includes whitespace, this output array will be longer than necessary.
    byte[] out = new byte[(int) (limit * 6L / 8L)];
    int outCount = 0;
    int inCount = 0;

    int word = 0;
    for (int pos = 0; pos < limit; pos++) {
      char c = in.charAt(pos);

      int bits;
      if (c >= 'A' && c <= 'Z') {
        // char ASCII value
        //  A    65    0
        //  Z    90    25 (ASCII - 65)
        bits = c - 65;
      } else if (c >= 'a' && c <= 'z') {
        // char ASCII value
        //  a    97    26
        //  z    122   51 (ASCII - 71)
        bits = c - 71;
      } else if (c >= '0' && c <= '9') {
        // char ASCII value
        //  0    48    52
        //  9    57    61 (ASCII + 4)
        bits = c + 4;
      } else if (c == '+' || c == '-') {
        bits = 62;
      } else if (c == '/' || c == '_') {
        bits = 63;
      } else if (c == '\n' || c == '\r' || c == ' ' || c == '\t') {
        continue;
      } else {
        return null;
      }

      // Append this char's 6 bits to the word.
      word = (word << 6) | (byte) bits;

      // For every 4 chars of input, we accumulate 24 bits of output. Emit 3 bytes.
      inCount++;
      if (inCount % 4 == 0) {
        out[outCount++] = (byte) (word >> 16);
        out[outCount++] = (byte) (word >> 8);
        out[outCount++] = (byte) word;
      }
    }

    int lastWordChars = inCount % 4;
    if (lastWordChars == 1) {
      // We read 1 char followed by "===". But 6 bits is a truncated byte! Fail.
      return null;
    } else if (lastWordChars == 2) {
      // We read 2 chars followed by "==". Emit 1 byte with 8 of those 12 bits.
      word = word << 12;
      out[outCount++] = (byte) (word >> 16);
    } else if (lastWordChars == 3) {
      // We read 3 chars, followed by "=". Emit 2 bytes for 16 of those 18 bits.
      word = word << 6;
      out[outCount++] = (byte) (word >> 16);
      out[outCount++] = (byte) (word >> 8);
    }

    // If we sized our out array perfectly, we're done.
    if (outCount == out.length) return out;

    // Copy the decoded bytes to a new, right-sized array.
    byte[] prefix = new byte[outCount];
    System.arraycopy(out, 0, prefix, 0, outCount);
    return prefix;
  }

  private static final byte[] MAP = new byte[] {
      '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', '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', '0', '1', '2', '3', '4',
      '5', '6', '7', '8', '9', '+', '/'
  };

  private static final byte[] URL_MAP = new byte[] {
      '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', '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', '0', '1', '2', '3', '4',
      '5', '6', '7', '8', '9', '-', '_'
  };

  public static String encode(byte[] in) {
    return encode(in, MAP);
  }

  public static String encodeUrl(byte[] in) {
    return encode(in, URL_MAP);
  }

  private static String encode(byte[] in, byte[] map) {
    int length = (in.length + 2) / 3 * 4;
    byte[] out = new byte[length];
    int index = 0, end = in.length - in.length % 3;
    for (int i = 0; i < end; i += 3) {
      out[index++] = map[(in[i] & 0xff) >> 2];
      out[index++] = map[((in[i] & 0x03) << 4) | ((in[i + 1] & 0xff) >> 4)];
      out[index++] = map[((in[i + 1] & 0x0f) << 2) | ((in[i + 2] & 0xff) >> 6)];
      out[index++] = map[(in[i + 2] & 0x3f)];
    }
    switch (in.length % 3) {
      case 1:
        out[index++] = map[(in[end] & 0xff) >> 2];
        out[index++] = map[(in[end] & 0x03) << 4];
        out[index++] = '=';
        out[index++] = '=';
        break;
      case 2:
        out[index++] = map[(in[end] & 0xff) >> 2];
        out[index++] = map[((in[end] & 0x03) << 4) | ((in[end + 1] & 0xff) >> 4)];
        out[index++] = map[((in[end + 1] & 0x0f) << 2)];
        out[index++] = '=';
        break;
    }
    try {
      return new String(out, "US-ASCII");
    } catch (UnsupportedEncodingException e) {
      throw new AssertionError(e);
    }
  }
}

The issue contains only a Java Base64Utils class and does not identify a repository file, test, requested change, or expected result. First inspect the repository context and the single issue comment to determine whether this code is intended for the blog and what completion criteria should be defined.