Make CANT_HAPPEN() more obvious for static analysis
Local analysis can now easily find out what's up. Before,
whole-program analysis was required. The Clang Static Analyzer
complained about code that is actually fine.
Stop ship and land unit movement on interdiction with no damage
Movement stops when shp_interdict() or lnd_interdict() report
interdiction. However, they reported it only when there was
interdiction damage.
Zero interdiction damage commonly happens when interdicting missiles
miss, or all bombers abort. Stopping regardless of damage makes more
sense there.
Moreover, not stopping is buggy: do_unit_move() needs to take care not
to wipe out updates made by interdiction to the moving ships or land
units. It does so only when it stops. Updates made by interdiction
without interdiction damage could get wiped out, triggering a seqno
mismatch oops.
Known ways moving ships and land units can get updated by interdiction
despite there is no interdiction damage:
* Interdicting bombers get intercepted by planes based on a navigating
carrier, carrier gets charged petrol. The bug wipes out the petrol
use.
* Marching land units get interdicted by planes, but all planes miss.
Sufficiently large collateral damage to the sector can still damage
the land units. The bug wipes out the damage to land units.
To make shp_interdict() and lnd_interdict() report interdiction
regardless of damage, change lnd_missile_interdiction(),
lnd_fort_interdiction(), lnd_mission_interdiction(),
shp_missile_interdiction(), shp_fort_interdiction(),
shp_mission_interdiction() to return whether there was interdiction.
Before, they returned whether there was damage.
Change unit_interdict(), perform_mission(), perform_mission_land(),
perform_mission_ship(), perform_mission_msl(), and
perform_mission_bomb() to return -1 for no interdiction, so that
callers can distinguish no interdiction from interdiction with no
damage.
Simplify ask_olist and get_dlist() not to re-read land units
getland() is obviously redundant in get_dlist(), because the land unit
can't have changed since the previous read.
What's up with ask_olist() is less obvious. For each capable land
unit, ask_olist() asks the player whether to attack with it. If it
attacks, it gets copied into olist. Since asking the player yields
the processor, these copies can become stale. However, re-reading
fixes that just for the last one. Moreover, the code copes with stale
copies just fine: ask_olist() is always directly followed by
att_get_offense() or att_move_in_off(), and both replace the
potentially stale copy in olist.
Inline get_land()'s "first time" case into its callers
ask_olist() and get_dlist() called get_land() with llp->chrp still
null, which made it initialize parts of llp instead of performing its
usual integrity check. att_reacting_units() had the initialization
inline. Change the other two to match, and simplify get_land(). No
functional change.
shp_missile_interdiction() does nothing when there are no suitable
targets. Its users avoid to call it when there are none, probably to
save a few cycles. Optimize shp_missile_interdiction() for that case,
and simplify the callers.
Generation numbers to catch write back of stale copies
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.
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.
Store uids as int to support more sectors and units
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.
Remove unused members of struct lndstr, lonstr, nukstr, trtstr
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.
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.
Don't intercept tactical and marine missiles targeting planes
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.
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.
Fix missiles interdicting ships outside range or op area
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.
Improve launch diagnostic messages, switch off supply
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.
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.
The various bombing functions silently skipped planes not carrying
bombs. This sanity check was wrong: it checked capabilities "tactical
or not cargo" instead of "tactical or bomber", and failed for
non-tactical cargo bombers. No such planes exist in the stock game.
The broken check comes from Chainsaw; it replaced an equally wrong
"not cargo" check.
Because pln_sel() lets only suitable planes go on a bombing run, the
broken sanity check is unnecessary. Drop it.
There are three ways to fly cargo: transport (fly command with a
commodity argument), cargo drops (drop command that isn't a sea mine
drop), and paradrops.
A cargo flight can be either an airlift or an airdrop. Airlifts carry
more cargo than airdrops. A cargo drop or paradrop with a non-VTOL
plane is an airdrop. Anything else is an airlift.
Before, paradrop always behaved like an airdrop, regardless of VTOL,
and drop always like an airlift. This made little sense.
Effect of the change on the stock game: paradrop with tc carries twice
the punch, and np/tr/jt can drop less than they can fly. In
particular, tr can't drop guns anymore, and jt can drop only one
instead of three.
Simplify plane selection for drop, fly, recon and sweep
Plane flying commands first select the planes to fly the mission and
their escorts, then equip them. They all fail when no planes to fly
the mission can be equipped.
Unlike bomb and paradrop, commands drop, fly, recon and sweep had an
additional check that made them fail when no planes to fly the mission
could be selected. Because "none selected" implies "none equipped",
the additional check is redundant. Remove it.
While there, break lines in calls of pln_sel() more tastefully.
Before, bomb selected any plane, but planes with zero load could not
be equipped. Cargo planes could be equipped fine, and they flew bombs
to the target, where they silently vanished.
Initially, paradrop capability was implied both by capability cargo
and by capability VTOL. Chainsaw changed para() to require cargo, and
added compile-time option PARAFLAG to additionally require new
capability para. The optional PARAFLAG rule became mandatory in
Empire 2.
Chainsaw left the old tests for "cargo or VTOL" in place. Because
para() checked "cargo and para" first, the old tests for "cargo or
VTOL" always passed, so they had no effect.
Make passing paradrop & mine cargo to pln_arm() & friends optional
These missions imply the cargo type, just like bombing missions. Use
the implied type instead of cargo type parameter ip there. Parameter
ip is now optional except for missions 't' (transport) and 'd' (drop).
Simplify para() not to pass the optional cargo type. Leave drop()
alone, because always passing the type is simpler there.
pln_arm(), pln_equip(), mission_pln_arm() mission_pln_equip() took a
mission parameter encoding the kind of sortie (strategic bomb,
pinpoint bomb, transport, ...), a flag parameter to further specify
the plane's role, and a parameter ip to specify the load.
The flags argument was always either P_F (intercept), P_F | P_ESC
(escort), or zero (any other role).
With non-zero flags, mission and ip argument were not used in any way.
Use mission 'e' and null load for escorts, and remove flags.
Intercept can still be identified by mission zero.
Also change pln_mobcost() to take a mission parameter instead of
flags, so that pln_arm() and mission_pln_arm() can simply pass on
their mission.
Check the true load instead of the ip parameter. Makes a difference
only when callers pass a bogus ip that isn't actually used. Happens
for escorts, but then the call can only be reached for deities,
because for mortals the transports fail before the escorts.
Don't print hit chance for nuclear warheads, it's always 100%.
Instead, print "Arming nuclear warheads" there. That message is now
printed after interception instead of before.
Before, it took a sector argument, and targeted the lowest-numbered
satellite there. Rather inconvenient when your own satellite masks
one of the enemy's.
Moreover, the command could be abused to find all sectors with
satellites. Now it can "only" be abused to find satellite ids, and
whether they're in range. Still not ideal, but tolerable.
Fix value of detonate() when target sector takes no damage
This can happen when hitting a sanctuary, or for ridiculously impotent
nukes: groundburst for dam < 5, airburst for dam < 7. detonate()
returned unpredictable value then.
This screwed up interdiction damage, except for missiles interdicting
ships or land units. Since nothing can move into a sanctuary, the bug
bit only with ridiculously impotent nukes.
Fix prod() to limit level production to resource contents
This could make production command mispredict resource-depleting level
production. Stock game is not affected. In fact, such a product
would be highly unusual.
Fix use of invalid pointer when depleting resource "none"
prod() and produce() dereferenced resource uninitialized for products
depleting resource "none" (p_nrdep != 0 && p_nrndx == 0). The latter
even wrote to it.
Depleting "none" makes no sense, and the depletion is now ignored.
Before, it could conceivably crash the server or corrupt the game.
projects / empserver / log