code: public static void writeByte(byte[] buf, int pos, byte v) {
      checkBoundary(buf, pos, 1);
      buf[pos] = v;
    }
docs: Writes a single byte value (1 byte) to the output byte array at the given offset.
  
  @param buf output byte buffer
  @param pos offset into the byte buffer to write
  @param v byte value to write