Keyless SipHash snippet

SipHash.snip.scala

// In this snippet, `buf`, `size` and `index` are provided by the containing class.
// The implementation is adapted from https://131002.net/siphash/siphash24.c

    def computeChecksum = {
      // SipHash implementation, but without cryptographic key initialisation.
      val s  = size - 8
      val bodyend = 8 * (s / 8)
      var v0 = 0x736f6d6570736575L
      var v1 = 0x646f72616e646f6dL
      var v2 = 0x6c7967656e657261L
      var v3 = 0x7465646279746573L
      var b  = s << 56
      var m  = 0L
      def rotl(x: Long, b: Int) = (x << b) | ( x >> (64 - b))
      def sipround() {
        v0 += v1
        v1 = rotl(v1, 13) ^ v0
        v0 = rotl(v0, 32)
        v2 += v3
        v3 = rotl(v3, 16) ^ v2
        v0 += v3
        v3 = rotl(v3, 21) ^ v0
        v2 += v1
        v1 = rotl(v1, 17) ^ v2
        v2 = rotl(v2, 32);
      }

      var i = 0L
      while (i < bodyend) {
        m = buf.getLong(index(i))
        i += 8
        v3 ^= m
        sipround
        sipround
        v0 ^= m
      }

      i = s & 7
      var shift = 48
      while (i > 0) {
        b |= buf.getByte(index(bodyend + i)) << shift
        shift -= 8
        i -= 1
      }

      v3 ^= b
      sipround
      sipround
      v0 ^= b
      v2 ^= 0xff
      sipround
      sipround
      sipround
      sipround
      v0 ^ v1 ^ v2  ^ v3
    }