code: static int writeAscii(AbstractByteBuf buffer, int writerIndex, CharSequence seq, int len) {
  
          // We can use the _set methods as these not need to do any index checks and reference checks.
          // This is possible as we called ensureWritable(...) before.
          for (int i = 0; i < len; i++) {
              buffer._setByte(writerIndex++, AsciiString.c2b(seq.charAt(i)));
          }
          return len;
      }
docs: Fast-Path implementation