Oops when a stale copy is written back, i.e. the processor was yielded
since the copy was made. Such bugs are difficult to spot. Sequence
numbers catch them when they do actual harm (they also catch different
bugs). Generation numbers catch them even when they don't.
New ef_generation to count generations. Call new ef_make_stale() to
increment it whenever the processor may be yielded.
New struct emptypedstr member generation. To conserve space, make it
a bit-field of twelve bits, i.e. generations are only recorded modulo
2^12. Make sure all members of unit empobj_storage share it. It is
only used in copies; its value on disk and in the cache is
meaningless. Copies with generation other than ef_generation are
stale. Stale copies that are a multiple of 2^12 generations old can't
be detected, but that is sufficiently improbable.
Set generation to ef_generation by calling new ef_mark_fresh() when
making copies in ef_read() and ef_blank(). nav_ship() and
fltp_to_list() make copies without going through ef_read(), and
therefore need to call ef_mark_fresh() as well. Also call it in
obj_changed() to make check_sect_ok() & friends freshen their argument
when it is unchanged.
New must_be_fresh() oopses when its argument is stale. Call it in
ef_write() to catch write back of stale copies.
Store them and ef_type in bit-fields.
Allocate eight bits for ef_type. Values range from 0 to EF_GAME
(currently 16), so this is plenty.
Allocate twelve bits for sequence numbers. Sequence number mismatches
are now missed when the numbers are equal modulo 2^12. Still
sufficiently improbable.
Common machines store the bit-fields in a 32 bit word. There are
twelve bits left in that word for future use. Total savings 16 bits,
which is exactly what the previous commit spent on wider uids on
common machines.
Before, they were stored as short. Wider uids use more space, but the
next commit will recover it by narrowing other members.
The use of short has always limited the number of ships, planes, land
units and nukes to SHRT_MAX (commonly 32768). Only the most extreme
games ever came close.
Commit 49780e2c (v4.3.12) added struct sctstr member sct_uid to make
struct empobj member uid work for sectors. This made the limit apply
to sectors as well. We've had games with more than 32768 sectors.
A sequence number mismatch occurs when an invalid copy (with a stale
sequence number) gets written. To continue after the error, we need
to use the current sequence number. But new_seqno() used the larger
one of the two, which is correct only as long as sequence numbers do
not overflow. Overflow is rather unlikely, though.
Member nws_uid is unused since the commit before previous. Remove it.
Member nws_seqno is of marginal value, because we write news only
through ncache[], and thus aren't prone to the errors sequence numbers
can catch. Remove it.
Make timestamp selector virtual, computing nws_when + nws_duration,
and remove member nws_timestamp. Impact:
* In ncache(), the removed timestamp equals nws_when + nws_duration,
both for new news and updated news. No change.
* delete_old_news() becomes invisible. Before, its move of unexpired
news to the beginning of the news file touched all the timestamps.
That was unwanted, because the move does not change news, only their
storage. Improvement.
* empdump no longer flags the imported news changed via the timestamp.
This is somewhat unfortunate. Document as bug.
With these members removed, struct nwsstr no longer matches struct
emptypedstr, so clear news table flag EFF_TYPED and remove union
empobj_storage member news. This loses the automatic maintenance of
member ef_type via struct emptypedstr. Remove ef_type as well.
This shrinks struct nwsstr from 20 to 12 bytes on common 32 bit
machines, and from 32 to 16 bytes on common 64 bit machines. Since
the server doesn't map the whole news file (EFF_MAP is off), this
reduces I/O, while the table's memory use remains the same.
Historical note: struct nwsstr is now pretty much what it was back in
BSD Empire 1.1. Members ef_type and nws_uid go back to Empire 3 (for
C_SYNC?). v4.3.12 added member nws_timestamp, which doubled the size
on common 64 bit machines. v4.3.15 added nws_seqno.
struct lndstr member lnd_flags is a leftover from Empire3's C_SYNC,
which was ripped out in 4.0.0.
struct lonstr member l_sel, struct nuk_str members nuk_ship, nuk_land,
and struct trtstr member trt_bond have been there basically forever
without any use.
Launching ABMs updates their base, in mission_pln_equip(). The update
got wiped out when launch_missile() wrote back the target sector,
triggering a seqno mismatch oops. Harmless with the stock game's
ABMs, because they use neither shells nor petrol.
Fix by re-reading the target sector.
Ships can expend shells to defend against missiles, in
shp_missile_defense(). Any shell use by the target ship got wiped out
when launch_missile() wrote back the target ship, triggering a seqno
mismatch oops.
Fix by re-reading the target ship.
Missiles attacking ground targets (sectors, ships or land units) can
be intercepted, missiles targeting planes can't. Except msl_launch()
checked the missile's capabilities instead of its target, and thus
intercepted missiles that *could* target ground even when they
targeted planes.
This broke the missile interception code's assumption that
interceptors aren't intercepted, and crashed the server through
infinite recursion: tactical abm #1 intercepts, tactical abm #2
intercepts #1, #1 intercepts #2, ...
Same bug in msl_hit() printed "incoming missile" for missiles that
could target ground but do target planes.
Broken in Empire 2. Bug can't bite with the stock game's planes.
Collateral damage was disabled, because after msl_hit() reported a
miss, the missile may or may not have reached the target.
Fix by splitting msl_launch() off msl_hit().
Drop the disabled collateral damage code for sector targets, because
sectors can't be missed. Enable it for ships and land units.
Since msl_launch() returns whether the missile is sub-launched, drop
launch_missile() parameter sublaunch, and simplify its caller.
Keep only the common part in msl_intercept(), and give it internal
linkage. Wrap new msl_abm_intercept() and msl_asat_intercept() around
it. They are simpler to use.
Ship interdiction works sector by sector. Interdicting missiles
targeted all ships not yet interdicted, not just the ones in the
current sector. This could lead to interdiction outside missile range
or op area.
Before Empire 2, nukes could be delivered only with bomb (special
mission 'n', airburst only) and launch (targeting sectors or
satellites only).
Empire 2 made nukes available for any kind of bombing, and for any
missile strike on sectors or ships. This included interdiction and
support missions. Nuclear-tipped anti-sats and bomb mission n were
removed.
Unfortunately, this was done in a messy way, which led to
inconsistencies and bugs. The problem is that ordinary damage affects
just the target, while nuke damage affects an area. Code dealing with
plane damage was designed for the former. Instead of rewriting it to
cope with area damage cleanly, nuke damage got shoehorned into
pln_damage(), the function to compute conventional plane damage, as a
side effect: computing damage blasted sectors in the area.
If the plane carried a nuke, pln_damage() returned zero (conventional)
damage. Without further logic, this simply bypassed the code to apply
damage to the target. This worked out okay when the target already
got damaged correctly by the side effect.
However, some targets are immune to the side effect: when interdicting
a move or explore command, the commodities being moved are not in any
sector.
For other targets, damage has effects other than damaging the target:
offensive and defensive support don't apply the (conventional) damage
to the target sector. Instead, they turn it into a combat bonus.
Without further logic, nuclear damage doesn't contribute to that.
To make all that work, pln_damage() returned the nuclear damage for
ground zero as well. Because a plane does either conventional or
nuclear damage, one of them is always zero.
Most callers simply ignored the nuclear damage, and applied only the
conventional damage.
Bug: land units and ships failed to retreat when pin-bombed or
missiled with a nuke. That's because they received zero conventional
damage.
The mission code flies planes and missiles and tallies their damage.
This mission damage included nuclear damage at ground zero (except for
missiles sometimes, see below), to make support and commodity
interdiction work. Unfortunately, this broke other things.
Bug: when bombers interdicted ships or land units, nukes first damaged
the ships or land units by the side effect, then again through mission
damage. Interdicting missiles had a special case to avoid this.
Bug: when interdicting move, explore or transport, nukes first damaged
the sector by the side effect, then again through mission damage's
collateral damage.
There may well be more bugs hiding in this mess.
The mess is not worth fixing. While the idea of interdicting and
supporting with nukes sounds kind of cool, I believe it's pretty
irrelevant in actual play.
Instead, go back to a variation of the original rules: nukes can be
delivered only through bomb mission 's' and launch at sectors.
Make arm reject marine missiles in addition to satellites, ABMs and
SAMs, and clear the mission. Make mission reject planes armed with
nukes. Oops when they show up in mission_pln_equip() anyway.
Make pln_equip() allow planes with nukes only for missions 's' and
't'.
Clean up pln_damage() to just compute damage, without side effect.
Change strat_bomb() and launch_missile() to detonate nukes. Simplify
the other callers. Parameter mission of msl_launch_mindam() is now
unused, remove it.
Missiles exploding on launch no longer set off their nukes. That was
pretty ridiculous anyway.
msl_equip() used mission_pln_equip(), which is for automatic defenses,
and therefore silent. Its users launch_as(), launch_missile() and
launch_sat() printed failure diagnostics based on assumptions on what
could go wrong.
Switch to the appropriate function for commands, pln_equip(), and
remove the guesswork. Implement mission 'i' there. When launching
from a foreign base, its owner now gets informed. Unimportant at this
time, as players can't easily deploy missiles in foreign bases.
This change also switches off automatic supply for launch. Consistent
with bomb.
When a manually launched anti-sat hits, it now always destroys the
satellite. This matches what it does when it intercepts
automatically. Before, it only damaged the satellite.
Before, satellites could be disarmed and armed even in orbit. Nukes
on satellites went along into orbit, where they did nothing in
particular.
Nukes on ABMs and SAMs were lost without effect when their missile
intercepted.
The stock game is not affected, because its satellites, ABMs and SAMs
all have zero load.
These were leftovers from Chainsaw, and their only remaining effect
was a flak bonus.
The got replaced except for flak by plane selector stealth under
Chainsaw option STEALTHV, which became mandatory in Empire 2. It is
unclear why STEALTHV didn't cover flak. No planes with these
capabilities have existed in the stock game since Empire 2.
