[Freeciv-Dev] (PR#9802) generic_city_refresh speedup via caching

["Benoit Hudson" <bh@xxxxxxxxxxxxxxxxxxx>]

<URL: http://rt.freeciv.org/Ticket/Display.html?id=9802 >

The major cost in the CM (>50%) is generic_city_refresh ; that's why we 
maintain all the 
fancy caches which distribute assumptions about game rules.  Looking at why 
this one 
function was so slow, I discovered it's because it computes a bunch of stuff 
that doesn't 
change across calls withing the CM -- which buildings exist, distance to the 
capital, etc etc.

This patch allows the CM to do:
(1) precompute various things, once per cm_query_result.
(2) quickly do the update, assuming everything was pre-computed, dozens of 
times.
And it does so transparently to almost all calling code.  It creates a new 
opaque field, that 
unfortunately citytools.c needs access to, so I created common/citycache.h 
(attached 
seperately since I don't know how to make cvs diff create it).

I've played almost a full game without problems that I could discern (except 
one I fixed), but 
this does change how some fairly fundamental calculations are done, so some 
scrutiny is in 
order.  I did a cvs update today to check, but it seems that even a clean build 
has an 
assertion failure as soon as I build a city, so all I can say is that this 
patch compiles, and once 
ran.

The patch reduces the CM time by about 10%.  After this, the main remaining 
cost of 
quick_city_refresh is evaluating the tiles, which could also be cached (that 
would be for a 
later patch).

city_quicker_refresh.diff
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citycache.h
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