[Freeciv-Dev] Population overflow (PR#987)

[awilkins@xxxxxxxxxxxx]

Full_Name: Alexander Wilkins
Version: 1.11.4
Distribution: Redhat binary
Client: Both (or N/A)
OS: Redhat Linux 7.1
Submission from: (NULL) (128.12.194.114)


When playing with a 200x100 world in such a manner as to maximize the 
number and size of my cities, I achieved a total population of more than
2^31 (2,147,483,648) people.  This overflowed the population counter, so 
that I now apparently have -2,133,487,296 people, rather than 
2,161,480,000.  

To reproduce:  Create a civilization with 250 size 41 cities. :)  As might
be expected, this takes time and terraforming (or editing the save file).

To fix:
1) Store population as a 32-bit unsigned int rather than a 32-bit signed
   int.  Problem:  This can probably be overflowed as well, since 500 size
   41 cities is still possible.

2) Since every city has a population that is a multiple of 10,000, only 
   store the total population / 10,000.   40 trillion people probably isn't
   possible.

3) Ignore.  Only obsessive-compulsives get civilizations this big anyway. 
   :)  The only visible effect of having having a negatively-sized 
   population is that you are last in the population demographics instead 
   of first.