long uniques aren't 32/64-bit portable

long uniques use internally Item_func_hash, which works as

longlong  Item_func_hash::val_int()

{

  DBUG_EXECUTE_IF("same_long_unique_hash", return 9;);

  unsigned_flag= true;

  ulong nr1= 1,nr2= 4;

  ...

  cs->hash_sort(l, sizeof(l), &nr1, &nr2);

  ...

  return   (longlong)nr1;

}

But ulong has a different size on 32-bit and 64-bit. All other code that uses hash_sort(), seems to be using only the lower 32-bit of the returned hash value. This item uses all 64, which makes hash values dependent on whether the platform is 32-bit or 64-bit.

Considerations:

• a simple fix would be to use only the lowest 32 bit from nr1 in the Item_func_hash::val_int(), but perhaps this hash function should internally use uint32 and be changed everywhere?
• perhaps HA_HASH_FIELD_LENGTH should be 4 not 8?
• compatibility. how to fix it and not break existing tables?