ref: cbe4b116989c0bfec49b9ae7a1d9a85ead6648ae
dir: /sys/src/libsat/satsolve.c/
#include <u.h>
#include <libc.h>
#include <sat.h>
#include "impl.h"
/* the solver follows Algorithm C from Knuth's The Art of Computer Programming, Vol. 4, Fascicle 6 */
#define verbosestate 0
#define verboseforcing 0
#define verboseconflict 0
#define paranoia 0
#define sanity(s) if(paranoia) satsanity(s)
void
sataddtrail(SATSolve *s, int l)
{
s->trail[s->ntrail++] = l;
s->lit[l].val = 1;
s->lit[NOT(l)].val = 0;
s->var[VAR(l)].lvl = s->lvl;
s->agility -= s->agility >> 13;
if(((s->var[VAR(l)].flags ^ l) & 1) != 0)
s->agility += 1<<19;
if(verbosestate) satprintstate(s);
}
/* compute watchlists from scratch */
static void
rewatch(SATSolve *s)
{
SATLit *l;
SATClause *c;
int i, j, x;
for(l = s->lit; l < s->lit + 2*s->nvar; l++)
l->watch = nil;
for(c = s->cl; c != nil; c = c->next)
for(i = 0; i < 2; i++){
if(s->lit[c->l[i]].val == 0)
for(j = 2; j < c->n; j++)
if(s->lit[c->l[j]].val != 0){
x = c->l[i], c->l[i] = c->l[j], c->l[j] = x;
break;
}
c->watch[i] = s->lit[c->l[i]].watch;
s->lit[c->l[i]].watch = c;
}
}
/* jump back to decision level d */
void
satbackjump(SATSolve *s, int d)
{
int l;
SATVar *v;
if(s->lvl == d) return;
while(s->ntrail > s->decbd[d + 1]){
l = s->trail[--s->ntrail];
v = &s->var[VAR(l)];
if((v->flags & VARUSER) != 0){ /* don't delete user assignments */
s->ntrail++;
break;
}
s->lit[l].val = -1;
s->lit[NOT(l)].val = -1;
v->flags = v->flags & ~1 | l & 1;
v->lvl = -1;
v->reason = nil;
v->isbinreason = 0;
if(v->heaploc < 0)
satheapput(s, v);
}
s->lvl = d;
if(s->forptr > s->ntrail) s->forptr = s->ntrail;
if(s->binptr > s->ntrail) s->binptr = s->ntrail;
if(verbosestate) satprintstate(s);
}
static void
solvinit(SATSolve *s)
{
satdebuginit(s);
satheapreset(s);
s->decbd = satrealloc(s, s->decbd, (s->nvar + 1) * sizeof(int));
s->decbd[0] = 0;
s->trail = satrealloc(s, s->trail, sizeof(int) * s->nvar);
s->fullrlits = satrealloc(s, s->fullrlits, sizeof(int) * s->nvar);
s->lvlstamp = satrealloc(s, s->lvlstamp, sizeof(int) * s->nvar);
memset(s->lvlstamp, 0, sizeof(int) * s->nvar);
if(s->cflclalloc == 0){
s->cflcl = satrealloc(s, s->cflcl, CFLCLALLOC * sizeof(int));
s->cflclalloc = CFLCLALLOC;
}
rewatch(s);
s->conflicts = 0;
s->nextpurge = s->purgeΔ;
s->purgeival = s->purgeΔ;
s->nextflush = 1;
s->flushu = 1;
s->flushv = 1;
s->flushθ = s->flushψ;
s->agility = 0;
satbackjump(s, 0);
s->forptr = 0;
s->binptr = 0;
}
void
satcleanup(SATSolve *s, int all)
{
SATBlock *b, *bn;
if(all){
*s->lastp[0] = nil;
s->learncl = nil;
s->lastp[1] = &s->learncl;
s->ncl = s->ncl0;
}
for(b = s->bl[1].next; b != &s->bl[1]; b = bn){
bn = b->next;
if(b->last != nil && !all) continue;
b->next->prev = b->prev;
b->prev->next = b->next;
free(b);
}
s->lastbl = s->bl[1].prev;
free(s->fullrlits);
s->fullrlits = nil;
free(s->lvlstamp);
s->lvlstamp = nil;
free(s->cflcl);
s->cflcl = nil;
s->cflclalloc = 0;
}
static void
stampoverflow(SATSolve *s)
{
int i;
for(i = 0; i < s->nvar; i++){
s->var[i].stamp = 0;
s->lvlstamp[i] = 0;
}
s->stamp = -2;
}
/* "bump" the variable, i.e. increase its activity score. reduce all score when one exceeds MAXACTIVITY (1e100) */
static void
varbump(SATSolve *s, SATVar *v)
{
v->activity += s->Δactivity;
satreheap(s, v);
if(v->activity < MAXACTIVITY) return;
for(v = s->var; v < s->var + s->nvar; v++)
if(v->activity != 0){
v->activity /= MAXACTIVITY;
if(v->activity < ε)
v->activity = ε;
}
s->Δactivity /= MAXACTIVITY;
}
/* ditto for clauses */
static void
clausebump(SATSolve *s, SATClause *c)
{
c->activity += s->Δclactivity;
if(c->activity < MAXACTIVITY) return;
for(c = s->cl; c != nil; c = c->next)
if(c->activity != 0){
c->activity /= MAXACTIVITY;
if(c->activity < ε)
c->activity = ε;
}
s->Δclactivity /= MAXACTIVITY;
}
/* pick a literal. normally we pick the variable with highest activity from the heap. sometimes we goof and pick a random one. */
static void
decision(SATSolve *s)
{
SATVar *v;
s->decbd[++s->lvl] = s->ntrail;
if((uint)s->randfn(s->randaux) < s->goofprob){
v = s->heap[satnrand(s, s->nheap)];
if(v->lvl < 0)
goto gotv;
}
do
v = satheaptake(s);
while(v->lvl >= 0);
gotv:
sataddtrail(s, 2 * (v - s->var) + (v->flags & VARPHASE));
}
/* go through the watchlist of a literal that just turned out false. */
/* full == 1 records the first conflict and goes on rather than aborting immediately */
static SATClause *
forcing(SATSolve *s, int l, int full)
{
SATClause **cp, *rc, *c, *xp;
int v0;
int x, j;
cp = &s->lit[l].watch;
rc = nil;
if(verboseforcing) print("forcing literal %d\n", signf(l));
while(c = *cp, c != nil){
if(l == c->l[0]){
/* this swap implies that the reason r for a literal l always has r->l[0]==l */
x = c->l[1], c->l[1] = c->l[0], c->l[0] = x;
xp = c->watch[1], c->watch[1] = c->watch[0], c->watch[0] = xp;
}
assert(c->l[1] == l);
v0 = s->lit[c->l[0]].val;
if(v0 > 0) /* the clause is true anyway */
goto next;
for(j = 2; j < c->n; j++)
if(s->lit[c->l[j]].val != 0){
/* found another literal to watch for this clause */
if(verboseforcing) print("moving clause %+Γ onto watchlist %d\n", c, signf(c->l[j]));
*cp = c->watch[1];
x = c->l[j], c->l[j] = c->l[1], c->l[1] = x;
c->watch[1] = s->lit[x].watch;
s->lit[x].watch = c;
goto cont;
}
if(v0 == 0){
/* conflict */
if(!full) return c;
if(rc == nil) rc = c;
goto next;
}
if(verboseforcing) print("inferring %d using clause %+Γ\n", signf(c->l[0]), c);
sataddtrail(s, c->l[0]);
s->var[VAR(c->l[0])].reason = c;
next:
cp = &c->watch[1];
cont: ;
}
return rc;
}
/* forcing() for binary implications */
static uvlong
binforcing(SATSolve *s, int l, int full)
{
SATLit *lp;
int i, m;
uvlong rc;
lp = &s->lit[l];
rc = 0;
if(verboseforcing && lp->nbimp > 0) print("forcing literal %d (binary)\n", signf(l));
for(i = 0; i < lp->nbimp; i++){
m = lp->bimp[i];
switch(s->lit[m].val){
case -1:
if(verboseforcing) print("inferring %d using binary clause (%d) ∨ %d\n", signf(m), -signf(l), signf(m));
sataddtrail(s, m);
s->var[VAR(m)].binreason = NOT(l);
s->var[VAR(m)].isbinreason = 1;
break;
case 0:
if(verboseforcing) print("conflict (%d) ∨ (%d)\n", -signf(l), signf(m));
if(rc == 0) rc = (uvlong)NOT(l) << 32 | (uint)m;
if(!full) return rc;
break;
}
}
return rc;
}
/* check if we can discard the previously learned clause because the current one subsumes it */
static int
checkdiscard(SATSolve *s)
{
SATClause *c;
SATVar *v;
int q, j;
if(s->lastp[1] == &s->learncl) return 0;
c = (SATClause*) ((uchar*) s->lastp[1] - (uchar*) &((SATClause*)0)->next);
if(s->lit[c->l[0]].val >= 0) return 0; /* clause is a reason, hands off */
q = s->ncflcl;
for(j = c->n - 1; q > 0 && j >= q; j--){
v = &s->var[VAR(c->l[j])];
/* check if literal is in the current clause */
if(c->l[j] == s->cflcl[0] || (uint)v->lvl <= s->cfllvl && v->stamp == s->stamp)
q--;
}
return q == 0;
}
/* add the clause we just learned to our collection */
static SATClause *
learn(SATSolve *s, int notriv)
{
SATClause *r;
int i, l, triv;
/* clauses that are too complicated are not worth it. learn the trivial clause (all decisions negated) instead */
if(triv = !notriv && s->ncflcl > s->lvl + s->trivlim){
assert(s->lvl + 1 <= s->cflclalloc);
for(i = 1; i <= s->lvl; i++)
s->cflcl[i] = NOT(s->trail[s->decbd[s->lvl + 1 - i]]);
s->ncflcl = s->lvl + 1;
}
if(s->ncflcl == 1) /* unit clauses are handled by putting them on the trail in conflict() */
return nil;
if(!triv && checkdiscard(s))
r = satreplclause(s, s->ncflcl);
else
r = satnewclause(s, s->ncflcl, 1);
r->n = s->ncflcl;
memcpy(r->l, s->cflcl, s->ncflcl * sizeof(int));
for(i = 0; i < 2; i++){
l = r->l[i];
r->watch[i] = s->lit[l].watch;
s->lit[l].watch = r;
}
return r;
}
/* recursive procedure to determine if a literal is redundant.
* to avoid repeated work, each known redundant literal is stamped with stamp+1
* and each known nonredundant literal is stamped with stamp+2.
*/
static int
redundant(SATSolve *s, int l)
{
SATVar *v, *w;
SATClause *c;
int i, r;
v = &s->var[VAR(l)];
if(v->isbinreason){
/* stupid special case code */
r = v->binreason;
w = &s->var[VAR(r)];
if(w->lvl != 0){
if(w->stamp == s->stamp + 2)
return 0;
if(w->stamp < s->stamp && (s->lvlstamp[w->lvl] < s->stamp || !redundant(s, r))){
w->stamp = s->stamp + 2;
return 0;
}
}
v->stamp = s->stamp + 1;
return 1;
}
if(v->reason == nil) return 0; /* decision literals are never redundant */
c = v->reason;
for(i = 0; i < c->n; i++){
if(c->l[i] == NOT(l)) continue;
w = &s->var[VAR(c->l[i])];
if(w->lvl == 0)
continue; /* literals at level 0 are redundant */
if(w->stamp == s->stamp + 2)
return 0;
/* if the literal is not in the clause or known redundant, check if it is redundant */
/* we can skip the check if the level is not stamped: */
/* if there are no literals at the same level in the clause, it must be nonredundant */
if(w->stamp < s->stamp && (s->lvlstamp[w->lvl] < s->stamp || !redundant(s, c->l[i]))){
w->stamp = s->stamp + 2;
return 0;
}
}
v->stamp = s->stamp + 1;
return 1;
}
/* "blitting" a literal means to either add it to the conflict clause
* (if v->lvl < s->lvl) or to increment the counter of literals to be
* resolved, plus some bookkeeping. */
static void
blit(SATSolve *s, int l)
{
SATVar *v;
int p;
v = &s->var[VAR(l)];
if(v->stamp == s->stamp) return;
v->stamp = s->stamp;
p = v->lvl;
if(p == 0) return;
if(verboseconflict) print("stamp %d %s (ctr=%d)\n", signf(l), p == s->lvl ? "and increment" : "and collect", s->cflctr);
varbump(s, v);
if(p == s->lvl){
s->cflctr++;
return;
}
if(s->ncflcl >= s->cflclalloc){
s->cflcl = satrealloc(s, s->cflcl, (s->cflclalloc + CFLCLALLOC) * sizeof(int));
s->cflclalloc += CFLCLALLOC;
}
s->cflcl[s->ncflcl++] = l;
if(p > s->cfllvl) s->cfllvl = p;
/* lvlstamp[p] == stamp if there is exactly one literal and ==stamp+1 if there is more than one literal on level p */
if(s->lvlstamp[p] <= s->stamp)
s->lvlstamp[p] = s->stamp + (s->lvlstamp[p] == s->stamp);
}
/* to resolve a conflict, we start with the conflict clause and use
* resolution (a ∨ b and ¬a ∨ c imply b ∨ c) with the reasons for the
* literals to remove all but one literal at the current level. this
* gives a new "learned" clause with all literals false and we jump back
* to the second-highest level in it. at this point, the clause implies
* the one remaining literal and we can continue.
* to do this quickly, rather than explicitly apply resolution, we keep a
* counter of literals at the highest level (unresolved literals) and an
* array with all other literals (which will become the learned clause). */
static void
conflict(SATSolve *s, SATClause *c, uvlong bin, int full)
{
int i, j, l, p, *nl, found;
SATVar *v;
SATClause *r;
if(verboseconflict) satprintstate(s);
/* choose a new unique stamp value */
if(s->stamp >= (uint)-3)
stampoverflow(s);
s->stamp += 3;
s->ncflcl = 1;
s->cflctr = 0;
s->cfllvl = 0;
/* we start by blitting each literal in the conflict clause */
if(c != nil){
clausebump(s, c);
for(i = 0; i < c->n; i++)
blit(s, c->l[i]);
/* if there is only one literal l at the current level, we should have inferred ¬l at a lower level (bug). */
if(s->cflctr <= 1){
satprintstate(s);
print("conflict clause %+Γ\n", c);
assert(s->cflctr > 1);
}
}else{
blit(s, bin);
blit(s, bin>>32);
if(s->cflctr <= 1){
satprintstate(s);
print("binary conflict clause %d ∨ %d\n", (int)(bin>>32), (int)bin);
assert(s->cflctr > 1);
}
}
/* now we go backwards through the trail, decrementing the unresolved literal counter at each stamped literal */
/* and blitting the literals in their reason */
for(i = s->ntrail; --i >= 0; ){
v = &s->var[VAR(s->trail[i])];
if(v->stamp != s->stamp) continue;
if(verboseconflict) print("trail literal %d\n", signf(s->trail[i]));
if(--s->cflctr == 0) break;
if(v->isbinreason)
blit(s, v->binreason);
else if((r = v->reason) != nil){
clausebump(s, r);
for(j = 0; j < r->n; j++)
blit(s, r->l[j]);
}
}
/* i should point to the one remaining literal at the current level */
assert(i >= 0);
nl = s->cflcl;
nl[0] = NOT(s->trail[i]);
found = 0;
/* delete redundant literals. note we must watch a literal at cfllvl, so put it in l[1]. */
for(i = 1, j = 1; i < s->ncflcl; i++){
l = nl[i];
p = s->var[VAR(nl[i])].lvl;
/* lvlstamp[p] != s->stamp + 1 => only one literal at level p => must be nonredundant */
if(s->lvlstamp[p] != s->stamp + 1 || !redundant(s, l))
if(found || p < s->cfllvl)
nl[j++] = nl[i];
else{
/* watch this literal */
l = nl[i], nl[j++] = nl[1], nl[1] = l;
found = 1;
}
}
s->ncflcl = j;
if(!full){
/* normal mode: jump back and add to trail right away */
satbackjump(s, s->cfllvl);
sataddtrail(s, nl[0]);
}else{
/* purging: record minimum cfllvl and literals at that level */
if(s->cfllvl < s->fullrlvl){
s->fullrlvl = s->cfllvl;
s->nfullrlits = 0;
}
s->fullrlits[s->nfullrlits++] = nl[0];
}
r = learn(s, full);
if(!full && r != nil)
s->var[VAR(nl[0])].reason = r;
if(verboseconflict)
if(r != nil)
print("learned %+Γ\n", r);
else
print("learned %d\n", signf(nl[0]));
s->Δactivity *= s->varρ;
s->Δclactivity *= s->clauseρ;
s->conflicts++;
}
/* to purge, we need a fullrun that assigns values to all variables.
* during this we record the first conflict at each level, to be resolved
* later. otherwise this is just a copy of the main loop which never
* purges or flushes. */
static int
fullrun(SATSolve *s)
{
int l;
uvlong b;
SATClause *c;
while(s->ntrail < s->nvar){
decision(s);
re:
while(s->binptr < s->ntrail){
l = s->trail[s->binptr++];
b = binforcing(s, l, 1);
if(b != 0){
if(s->lvl == 0){
s->unsat = 1;
return -1;
}
if(s->nfullrcfl == 0 || s->lvl > CFLLVL(s->fullrcfl[s->nfullrcfl-1])){
s->fullrcfl = satrealloc(s, s->fullrcfl, sizeof(SATConflict) * (s->nfullrcfl + 1));
s->fullrcfl[s->nfullrcfl].lvl = 1<<31 | s->lvl;
s->fullrcfl[s->nfullrcfl++].b = b;
}
}
sanity(s);
}
while(s->forptr < s->ntrail){
l = s->trail[s->forptr++];
c = forcing(s, NOT(l), 1);
if(c != nil){
if(s->lvl == 0){
s->unsat = 1;
return -1;
}
if(s->nfullrcfl == 0 || s->lvl > CFLLVL(s->fullrcfl[s->nfullrcfl-1])){
s->fullrcfl = satrealloc(s, s->fullrcfl, sizeof(SATConflict) * (s->nfullrcfl + 1));
s->fullrcfl[s->nfullrcfl].lvl = s->lvl;
s->fullrcfl[s->nfullrcfl++].c = c;
}
}
}
if(s->binptr < s->ntrail) goto re;
}
return 0;
}
/* assign range scores to all clauses.
* p == number of levels that have positive literals in the clause.
* r == number of levels that have literals in the clause.
* range == min(floor(16 * (p + α (r - p))), 255) with magic constant α. */
static void
ranges(SATSolve *s)
{
SATClause *c;
int p, r, k, l, v;
uint ci;
ci = 2;
memset(s->lvlstamp, 0, sizeof(int) * s->nvar);
memset(s->rangecnt, 0, sizeof(s->rangecnt));
for(c = s->learncl; c != nil; c = c->next, ci += 2){
if(!s->var[VAR(c->l[0])].binreason && s->var[VAR(c->l[0])].reason == c){
c->range = 0;
s->rangecnt[0]++;
continue;
}
p = 0;
r = 0;
for(k = 0; k < c->n; k++){
l = c->l[k];
v = s->var[VAR(l)].lvl;
if(v == 0){
if(s->lit[l].val == 1){
c->range = 256;
goto next;
}
}else{
if(s->lvlstamp[v] < ci){
s->lvlstamp[v] = ci;
r++;
}
if(s->lvlstamp[v] == ci && s->lit[l].val == 1){
s->lvlstamp[v] = ci + 1;
p++;
}
}
}
r = 16 * (p + s->purgeα * (r - p));
if(r > 255) r = 255;
c->range = r;
s->rangecnt[r]++;
next: ;
}
}
/* resolve conflicts found during fullrun() */
static void
fullrconflicts(SATSolve *s)
{
SATConflict *cfl;
int i;
s->fullrlvl = s->lvl;
s->nfullrlits = 0;
for(cfl = &s->fullrcfl[s->nfullrcfl - 1]; cfl >= s->fullrcfl; cfl--){
satbackjump(s, CFLLVL(*cfl));
if(cfl->lvl < 0)
conflict(s, nil, cfl->b, 1);
else
conflict(s, cfl->c, 0, 1);
}
satbackjump(s, 0);
if(s->fullrlvl == 0)
for(i = 0; i < s->nfullrlits; i++)
sataddtrail(s, s->fullrlits[i]);
free(s->fullrcfl);
s->fullrcfl = nil;
}
/* note that nil > *, this simplifies the algorithm by having nil "bubble" to the top */
static int
actgt(SATClause *a, SATClause *b)
{
if(b == nil) return 0;
if(a == nil) return 1;
return a->activity > b->activity || a->activity == b->activity && a > b;
}
/* select n clauses to keep
* first we find the upper limit j on the range score
* to get the exact number, we move htot clauses from j to j+1
* to this end, we put them in a max-heap of size htot, sorted by activity,
* continually replacing the largest element if we find a less active clause.
* the heap starts out filled with nil and the nil are replaced during the first
* htot iterations. */
#define LEFT(i) (2*(i)+1)
#define RIGHT(i) (2*(i)+2)
static int
judgement(SATSolve *s, int n)
{
int cnt, i, j, htot, m;
SATClause *c, **h, *z;
cnt = 0;
for(j = 0; j < 256; j++){
cnt += s->rangecnt[j];
if(cnt >= n) break;
}
if(j == 256) return j;
if(cnt > n){
htot = cnt - n;
h = satrealloc(s, nil, sizeof(SATClause *) * htot);
memset(h, 0, sizeof(SATClause *) * htot);
for(c = s->learncl; c != nil; c = c->next){
if(c->range != j || actgt(c, h[0])) continue;
h[0] = c;
m = 0;
for(;;){
i = m;
if(LEFT(i) < htot && actgt(h[LEFT(i)], h[m])) m = LEFT(i);
if(RIGHT(i) < htot && actgt(h[RIGHT(i)], h[m])) m = RIGHT(i);
if(i == m) break;
z = h[i], h[i] = h[m], h[m] = z;
}
}
for(i = 0; i < htot; i++)
if(h[i] != nil)
h[i]->range = j + 1;
free(h);
}
return j;
}
/* during purging we remove permanently false literals from learned clauses.
* returns 1 if the clause can be deleted entirely. */
static int
cleanupclause(SATSolve *s, SATClause *c)
{
int i, k;
for(i = 0; i < c->n; i++)
if(s->lit[c->l[i]].val == 0)
break;
if(i == c->n) return 0;
for(k = i; i < c->n; i++)
if(s->lit[c->l[i]].val != 0)
c->l[k++] = c->l[i];
c->n = k;
if(k > 1) return 0;
if(k == 0)
s->unsat = 1;
else if(s->lit[c->l[0]].val < 0)
sataddtrail(s, c->l[0]);
return 1;
}
/* delete clauses by overwriting them. don't delete empty blocks; we're going to fill them up soon enough again. */
static void
execution(SATSolve *s, int j)
{
SATClause *c, *n, **cp, *p;
SATBlock *b;
SATVar *v0;
int f, sz;
b = s->bl[1].next;
p = (SATClause*) b->data;
s->ncl = s->ncl0;
cp = &s->learncl;
for(c = p; c != nil; c = n){
n = c->next;
if(c->range > j || cleanupclause(s, c))
continue;
sz = sizeof(SATClause) + (c->n - 1) * sizeof(int);
f = (uchar*)b + SATBLOCKSZ - (uchar*)p;
if(f < sz){
memset(p, 0, f);
b = b->next;
assert(b != &s->bl[1]);
p = (SATClause *) b->data;
}
b->last = p;
/* update reason field of the first variable (if applicable) */
v0 = &s->var[VAR(c->l[0])];
if(!v0->isbinreason && v0->reason == c)
v0->reason = p;
memmove(p, c, sz);
*cp = p;
cp = &p->next;
p = (void*)((uintptr)p + sz + CLAUSEALIGN - 1 & -CLAUSEALIGN);
b->end = p;
s->ncl++;
}
*cp = nil;
*s->lastp[0] = s->learncl;
s->lastp[1] = cp;
s->lastbl = b;
f = (uchar*)b + SATBLOCKSZ - (uchar*)p;
memset(p, 0, f);
for(b = b->next; b != &s->bl[1]; b = b->next){
b->last = nil;
b->end = b->data;
}
}
static void
thepurge(SATSolve *s)
{
int nkeep, i, j;
SATVar *v;
s->purgeival += s->purgeδ;
s->nextpurge = s->conflicts + s->purgeival;
nkeep = (s->ncl - s->ncl0) / 2;
for(i = 0; i < s->ntrail; i++){
v = &s->var[VAR(s->trail[i])];
if(!v->isbinreason && v->reason != nil)
nkeep++;
}
if(nkeep <= 0) return; /* shouldn't happen */
s->nfullrcfl = 0;
if(fullrun(s) < 0){ /* accidentally determined UNSAT during fullrun() */
free(s->fullrcfl);
s->fullrcfl = nil;
return;
}
ranges(s);
fullrconflicts(s);
j = judgement(s, nkeep);
execution(s, j);
rewatch(s);
}
/* to avoid getting stuck, flushing backs up the trail to remove low activity variables.
* don't worry about throwing out high activity ones, they'll get readded quickly. */
static void
theflush(SATSolve *s)
{
double actk;
int dd, l;
/* "reluctant doubling" wizardry to determine when to flush */
if((s->flushu & -s->flushu) == s->flushv){
s->flushu++;
s->flushv = 1;
s->flushθ = s->flushψ;
}else{
s->flushv *= 2;
s->flushθ += s->flushθ >> 4;
}
s->nextflush = s->conflicts + s->flushv;
if(s->agility > s->flushθ) return; /* don't flush when we're too busy */
/* clean up the heap so that a free variable is at the top */
while(s->nheap > 0 && s->heap[0]->lvl >= 0)
satheaptake(s);
if(s->nheap == 0) return; /* shouldn't happen */
actk = s->heap[0]->activity;
for(dd = 0; dd < s->lvl; dd++){
l = s->trail[s->decbd[dd+1]];
if(s->var[VAR(l)].activity < actk)
break;
}
satbackjump(s, dd);
}
int
satsolve(SATSolve *s)
{
int l;
SATClause *c;
uvlong b;
if(s == nil) return 1;
if(s->scratched) return -1;
if(s->nvar == 0) return 1;
solvinit(s);
while(!s->unsat){
re:
while(s->binptr < s->ntrail){
l = s->trail[s->binptr++];
b = binforcing(s, l, 0);
sanity(s);
if(b != 0){
if(s->lvl == 0) goto unsat;
conflict(s, nil, b, 0);
sanity(s);
}
}
while(s->forptr < s->ntrail){
l = s->trail[s->forptr++];
c = forcing(s, NOT(l), 0);
sanity(s);
if(c != nil){
if(s->lvl == 0) goto unsat;
conflict(s, c, 0, 0);
sanity(s);
}
}
if(s->binptr < s->ntrail) goto re;
if(s->ntrail == s->nvar) goto out;
if(s->conflicts >= s->nextpurge)
thepurge(s);
else if(s->conflicts >= s->nextflush)
theflush(s);
else
decision(s);
}
unsat:
s->unsat = 1;
out:
satcleanup(s, 0);
return !s->unsat;
}
void
satreset(SATSolve *s)
{
int i;
if(s == nil || s->decbd == nil) return;
satbackjump(s, -1);
s->lvl = 0;
for(i = 0; i < s->nvar; i++){
s->var[i].activity = 0;
s->var[i].flags |= VARPHASE;
}
satcleanup(s, 1);
s->Δactivity = 1;
s->Δclactivity = 1;
}