hpack/src/main/java/com/twitter/hpack/Encoder.java
private static void encodeInteger(OutputStream out, int mask, int n, int i) throws IOException {
    if (n < 0 || n > 8) {
      throw new IllegalArgumentException("N: " + n);
    }
    int nbits = 0xFF >>> (8 - n);
    if (i < nbits) {
      out.write(mask | i);
    } else {
      out.write(mask | nbits);
      int length = i - nbits;
      while (true) {
        if ((length & ~0x7F) == 0) {
          out.write(length);
          return;
        } else {
          out.write((length & 0x7F) | 0x80);
          length >>>= 7;
        }
      }
    }
  }
private static void encodeInteger(OutputStream out, int mask, int n, int i) throws IOException {
    if (n < 0 || n > 8) {
      throw new IllegalArgumentException("N: " + n);
    }
    int nbits = 0xFF >>> (8 - n);
    if (i < nbits) {
      out.write(mask | i);
    } else {
      out.write(mask | nbits);
      int length = i - nbits;
      while (true) {
        if ((length & ~0x7F) == 0) {
          out.write(length);
          return;
        } else {
          out.write((length & 0x7F) | 0x80);
          length >>>= 7;
        }
      }
    }
  }
Encode integer according to Section 5.1.