uint64 Hash64StringWithSeed()

in src/kudu/gutil/hash/jenkins.cc [148:192]

• 40 lines of code
• 25 McCabe index (conditional complexity)

uint64 Hash64StringWithSeed(const char *s, uint32 len, uint64 c) {
  uint64 a, b;
  uint32 keylen;

  a = b = GG_ULONGLONG(0xe08c1d668b756f82);   // the golden ratio; an arbitrary value

  for ( keylen = len;  keylen >= 3 * sizeof(a);
        keylen -= 3 * static_cast<uint32>(sizeof(a)), s += 3 * sizeof(a) ) {
    a += Word64At(s);
    b += Word64At(s + sizeof(a));
    c += Word64At(s + sizeof(a) * 2);
    mix(a,b,c);
  }

  c += len;
  switch ( keylen ) {           // deal with rest.  Cases fall through
    case 23: c += char2unsigned64(s[22]) << 56;
    case 22: c += char2unsigned64(s[21]) << 48;
    case 21: c += char2unsigned64(s[20]) << 40;
    case 20: c += char2unsigned64(s[19]) << 32;
    case 19: c += char2unsigned64(s[18]) << 24;
    case 18: c += char2unsigned64(s[17]) << 16;
    case 17: c += char2unsigned64(s[16]) << 8;
      // the first byte of c is reserved for the length
    case 16: b += Word64At(s+8);  a += Word64At(s);  break;
    case 15: b += char2unsigned64(s[14]) << 48;
    case 14: b += char2unsigned64(s[13]) << 40;
    case 13: b += char2unsigned64(s[12]) << 32;
    case 12: b += char2unsigned64(s[11]) << 24;
    case 11: b += char2unsigned64(s[10]) << 16;
    case 10: b += char2unsigned64(s[ 9]) << 8;
    case  9: b += char2unsigned64(s[ 8]) ;
    case  8: a += Word64At(s);  break;
    case  7: a += char2unsigned64(s[ 6]) << 48;
    case  6: a += char2unsigned64(s[ 5]) << 40;
    case  5: a += char2unsigned64(s[ 4]) << 32;
    case  4: a += char2unsigned64(s[ 3]) << 24;
    case  3: a += char2unsigned64(s[ 2]) << 16;
    case  2: a += char2unsigned64(s[ 1]) << 8;
    case  1: a += char2unsigned64(s[ 0]) ;
      // case 0: nothing left to add
   }
   mix(a,b,c);
   return c;
}