code: public int indexOf(char ch, int start) {
          if (ch > MAX_CHAR_VALUE) {
              return INDEX_NOT_FOUND;
          }
  
          if (start < 0) {
              start = 0;
          }
  
          final byte chAsByte = c2b0(ch);
          final int len = offset + length;
          for (int i = start + offset; i < len; ++i) {
              if (value[i] == chAsByte) {
                  return i - offset;
              }
          }
          return INDEX_NOT_FOUND;
      }
docs: Searches in this string for the index of the specified char {@code ch}.
  The search for the char starts at the specified offset {@code start} and moves towards the end of this string.
  
  @param ch the char to find.
  @param start the starting offset.
  @return the index of the first occurrence of the specified char {@code ch} in this string,
  -1 if found no occurrence.