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Search depth in TT & small technical optimizations
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Search depth corrections:
- draw & mated paths are valid for any depth, so we give them a depth of 20
- when we get a score/path from TT, the TT entry depth will add to the
current search depth - putting such results again in TT with the cumulate depth
is a mistake and is not the same as if we searched to that total depth, so we
correct this - all lines like let de = max d (pathDepth s) deleted
- also as a result of the previous depth calculation of the found path it means
then path depts can get big, but our TT has only 6 bits for the depth,
so we limit the depth to 40 when we write to the TT
Other changes:
- small optimization in QS (call of qSearchLims)
- some renames
- some explaining comments
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@nionita
nionita committed Feb 17, 2024
1 parent ef92494 commit 7719231
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2 changes: 1 addition & 1 deletion Main/Barbarossa.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -39,7 +39,7 @@ progName, progVersion, progVerSuff, progAuthor :: String
progName = "Barbarossa"
progAuthor = "Nicu Ionita"
progVersion = "0.7.0"
progVerSuff = "coqs"
progVerSuff = "tecod"

data Options = Options {
optConfFile :: Maybe String, -- config file
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4 changes: 3 additions & 1 deletion Moves/Base.hs
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Expand Up @@ -363,7 +363,9 @@ ttStore !deep !tp !sc !bestm !nds = do
s <- get
p <- getPos
-- We use the type: 0 - upper limit, 1 - lower limit, 2 - exact score
liftIO $ writeCache (hash s) (zobkey p) deep tp sc bestm nds
-- Warning: depth has 6 bit in TT (so max 64)! We are currently still far from this,
-- but by summing different paths this could happen: so limit it here
liftIO $ writeCache (hash s) (zobkey p) (min 40 deep) tp sc bestm nds

-- History heuristic table update when beta cut
betaCut :: Int -> Move -> Game ()
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88 changes: 47 additions & 41 deletions Search/Albeta.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -35,7 +35,7 @@ useAspirWin = False
scoreGrain, depthForCM, minPvDepth :: Int
scoreGrain = 4 -- score granularity
depthForCM = 8 -- from this depth inform current move
minPvDepth = 2 -- from this depth we use alpha beta search
minPvDepth = 2 -- from this depth we use pv search
useTTinPv :: Bool
useTTinPv = False -- retrieve from TT in PV?

Expand Down Expand Up @@ -177,8 +177,8 @@ data Path
mated :: Int
mated = - mateScore
drawPath, matedPath :: Path
drawPath = Path { pathScore = 0, pathDepth = 0, pathMoves = Seq [] }
matedPath = Path { pathScore = mated, pathDepth = 0, pathMoves = Seq [] }
drawPath = Path { pathScore = 0, pathDepth = 20, pathMoves = Seq [] }
matedPath = Path { pathScore = mated, pathDepth = 20, pathMoves = Seq [] }

-- Making a path from a plain score:
pathFromScore :: Int -> Path
Expand Down Expand Up @@ -277,7 +277,7 @@ pvRootSearch :: Int -> Int -> Int -> Seq Move -> Alt Move -> Bool
pvRootSearch a b d lastpath rmvs aspir = do
pos <- lift getPos
edges <- if null (unalt rmvs) -- only when d==1, but we could have lastpath from the previous real move
then genAndSort nst0 { cpos = pos } Nothing a b d -- no IID here as d==1
then genAndPick nst0 { cpos = pos } Nothing a b d -- no IID here as d==1
else case lastpath of
Seq [] -> return rmvs -- does this happen? - check to simplify!
Seq (e:_) -> return $ Alt $ e : delete e (unalt rmvs)
Expand Down Expand Up @@ -343,13 +343,13 @@ pvInnerRoot b d nst e = timeToAbort (True, nst) $ do

pvInnerRootExten :: Int -> Int -> Int -> NodeState -> Search Path
pvInnerRootExten b d !exd nst = do
let !inPv = crtnt nst == PVNode
let !pvnode = crtnt nst == PVNode
!d1 = d + exd - 1 -- this is the normal (unreduced) depth for the next search
a = pathScore $ cursc nst
if inPv || d <= minPvDepth -- search of principal variation
if pvnode || d <= minPvDepth -- search of principal variation
then do
-- Set albe only when not in PV and not already set (to spare a copy)
let nst' = if not (inPv || albe nst) then nst { albe = True } else nst
let nst' = if not (pvnode || albe nst) then nst { albe = True } else nst
pnextlev <$> pvSearch nst' (-b) (-a) d1
else do
-- no futility pruning & no LMR for root moves!
Expand All @@ -374,7 +374,7 @@ checkFailOrPVRoot xstats b d e s nst = whenAbort (True, nst) $ do
!nodes1 = sNodes (stats sst) + sRSuc (stats sst)
!nodes' = nodes1 - nodes0
pvg = Pvsl s nodes' -- the good
de = max d $ pathDepth s
-- de = max d $ pathDepth s
-- Treat all depth the same
-- This also means, we do not have a known score for every root move
if pathScore s <= a
Expand All @@ -384,10 +384,10 @@ checkFailOrPVRoot xstats b d e s nst = whenAbort (True, nst) $ do
return (False, nst1)
else if pathScore s >= b
then do
-- what when a root move fails high? We are in aspiration
-- what when a root move fails high? We must be in aspiration
lift $ do
let typ = 1 -- beta cut (score is lower limit) with move e
ttStore de typ b e nodes'
ttStore d typ b e nodes'
betaCut (absdp sst) e
let xpvslg = insertToPvs d pvg (pvsl nst) -- the good
csc = s { pathScore = b }
Expand All @@ -399,7 +399,7 @@ checkFailOrPVRoot xstats b d e s nst = whenAbort (True, nst) $ do
informPV sc (draft $ ronly sst) pa
lift $ do
let typ = 2 -- best move so far (score is exact)
ttStore de typ sc e nodes'
ttStore d typ sc e nodes'
betaCut (absdp sst) e -- not really cut, but good move
let xpvslg = insertToPvs d pvg (pvsl nst) -- the good
nst1 = nst { cursc = s, nxtnt = nextNodeType (nxtnt nst),
Expand Down Expand Up @@ -428,18 +428,20 @@ pvSearch _ !a !b !d | d <= 0 = do
v <- pvQSearch a b
return $! pathFromScore v -- ok: fail hard in QS
pvSearch nst !a !b !d = do
let !inPv = crtnt nst == PVNode
ab = albe nst
let pvnode = crtnt nst == PVNode
-- Here we are always in PV if enough depth:
when (not $ inPv || ab) $ lift $ absurd $ "pvSearch: not inPv, not ab, nst = " ++ show nst
when (not $ pvnode || albe nst) $ lift $ absurd $ "pvSearch: not pvnode, not albe, nst = " ++ show nst
-- Check first for a TT entry of the position to search
(hdeep, tp, hsc, e, nodes') <- reTrieve >> lift ttRead
-- tp == 1 => score >= hsc, so if hsc >= asco then we improved,
-- but can we use hsc in PV? This score is not exact!
-- Idea: return only if better than beta, else search for exact score
-- tp == 0 => score <= hsc, so if hsc <= asco then we fail low and
-- Here we search for an exact score, either by alpha/beta search in the first few depths,
-- or by PV search, in all the higher depths. Looking in the TT we can get 3 cases:
-- tp == 2 => we got an exact score with the right depth: use it (return)
-- tp == 1 => score >= hsc, so if hsc >= a then we improved,
-- but we can't we use hsc in PV: the score is not exact!
-- So we use it (return) only if better than beta; otherwise search for exact score
-- tp == 0 => score <= hsc, so if hsc <= a then we fail low and
-- can terminate the search
if (useTTinPv || ab) && hdeep >= d && (
if hdeep >= d && (useTTinPv || albe nst) && (
tp == 2 -- exact score: always good
|| tp == 1 && hsc >= b -- we will fail high
|| tp == 0 && hsc <= a -- we will fail low
Expand All @@ -453,34 +455,39 @@ pvSearch nst !a !b !d = do
reSucc nodes' >> return ttpath
else do
when (hdeep < 0) reFail
-- Here: when ab we should do null move search
-- TODO: when albe, we should do null move search
pos <- lift getPos
-- Use the found TT move as best move
let mttmv = if hdeep > 0 then Just e else Nothing
!nst' = nst { cpos = pos }
edges <- genAndSort nst' mttmv a b d
edges <- genAndPick nst' mttmv a b d
if noMove edges
then return $! failHardNoValidMove a b pos
else do
nodes0 <- gets (sNodes . stats)
-- futility pruning:
-- Here we could maybe raise alpha when we got tp == 1 from TT, but with hsc < b:
-- if hsc > a then we know there must be something better than a, so we could search for it
-- If we do so, we should put a' = hsc - scoreGrain, so that we get at least
-- one variation. But the question is: is it possible that we don't find one?
-- And if yes: what to do in that case?
-- Futility pruning:
let !prune = isPruneFutil d a True (staticScore pos)
!nsti = resetNSt (pathFromScore a) (Killer []) nst'
-- Loop thru the moves
let !nsti = resetNSt (pathFromScore a) (Killer []) nst'
!nstf <- pvSLoop b d False prune nsti edges
let s = cursc nstf
whenAbort s $
if movno nstf == 1
then return $! failHardNoValidMove a b pos
else do
let de = max d $ pathDepth s
-- let de = max d $ pathDepth s
nodes1 <- gets (sNodes . stats)
lift $ do
let !deltan = nodes1 - nodes0
mvs = pathMoves s
mv | nullSeq mvs = head $ unalt edges -- not null - on "else" of noMove
| otherwise = head $ unseq mvs
ttStore de (rbmch nstf) (pathScore s) mv deltan
ttStore d (rbmch nstf) (pathScore s) mv deltan
return s

-- PV Zero Window
Expand Down Expand Up @@ -511,7 +518,7 @@ pvZeroW !nst !b !d = do
-- Use the TT move as best move
let mttmv = if hdeep > 0 then Just e else Nothing
!nst' = nst { cpos = pos }
edges <- genAndSort nst' mttmv bGrain b d
edges <- genAndPick nst' mttmv bGrain b d
if noMove edges
then return $! failHardNoValidMove bGrain b pos
else do
Expand All @@ -529,14 +536,14 @@ pvZeroW !nst !b !d = do
if movno nstf == 1
then return $! failHardNoValidMove bGrain b pos
else do
let !de = max d $ pathDepth s
-- let !de = max d $ pathDepth s
!nodes1 <- gets (sNodes . stats)
lift $ do
let !deltan = nodes1 - nodes0
mvs = pathMoves s
mv | nullSeq mvs = head $ unalt edges -- not null - on "else" of noMove
| otherwise = head $ unseq mvs
ttStore de (rbmch nstf) (pathScore s) mv deltan
ttStore d (rbmch nstf) (pathScore s) mv deltan
return s
where !bGrain = b - scoreGrain

Expand Down Expand Up @@ -640,13 +647,13 @@ resetSpc nst = nst { spcno = movno nst }

pvInnerLoopExten :: Int -> Int -> Bool -> Int -> NodeState -> Search Path
pvInnerLoopExten b d spec !exd nst = do
let !inPv = crtnt nst == PVNode
let !pvnode = crtnt nst == PVNode
!d1 = d + exd - 1 -- this is the normal (unreduced) depth for next search
a = pathScore $ cursc nst
if inPv || d <= minPvDepth
if pvnode || d <= minPvDepth
then do
-- Set albe only when not in PV and not already set (to spare a copy)
let nst' = if not (inPv || albe nst) then nst { albe = True } else nst
let nst' = if not (pvnode || albe nst) then nst { albe = True } else nst
pnextlev <$> pvSearch nst' (-b) (-a) d1
else do
-- Here we must be in a Cut node (will fail low)
Expand Down Expand Up @@ -715,8 +722,8 @@ checkFailOrPVLoop b d e s nst = whenAbort nst $ do
else do -- means: > a && < b
lift $ do
betaCut (absdp sst) e -- not really a cut, but good move here
let de = max d $ pathDepth s
ttStore de 1 (pathScore s) e 0 -- best move so far (score is lower limit)
-- let de = max d $ pathDepth s
ttStore d 1 (pathScore s) e 0 -- best move so far (score is lower limit)
let nnt = nextNodeType (nxtnt nst)
return $! nst { cursc = s, nxtnt = nnt, movno = mn+1, rbmch = 2 }

Expand Down Expand Up @@ -749,10 +756,10 @@ newTKiller pos d s
isTKillCand pos km = Killer [km]
| otherwise = Killer []

-- We don't sort the moves here, they have to come sorted from genMoves
-- But we consider the best move first (TT or IID) and the killers
genAndSort :: NodeState -> Maybe Move -> Int -> Int -> Int -> Search (Alt Move)
genAndSort !nst mttmv !a !b !d = do
-- We generate the moves, which come already sorted from genMoves
-- But we pick the best move (TT or IID) and the killers first
genAndPick :: NodeState -> Maybe Move -> Int -> Int -> Int -> Search (Alt Move)
genAndPick !nst mttmv !a !b !d = do
path <- case mttmv of
Just mv -> return [mv]
Nothing -> bestMoveFromIID nst a b d -- it will do nothing for AllNode
Expand Down Expand Up @@ -852,10 +859,9 @@ qSearchFound !a !b !tp !hsc front = do
-- This cannot happen in zero window search!
if a + scoreGrain == b
then qSearchLims a b front
else do
let (!a', !b') | tp == 1 = (max a hsc, b)
| otherwise = (a, min b hsc)
qSearchLims a' b' front
else if tp == 1
then qSearchLims (max a hsc) b front
else qSearchLims a (min b hsc) front

qSearchNotFound :: Int -> Int -> Bool -> Search Int
qSearchNotFound !a !b front = reFail >> qSearchLims a b front
Expand Down

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