git/query: refactor graph painting algorithm (findtwixt, lca)
We now keep track of 3 sets during traversal: - keep: commits we've reached from head commits - drop: commits we've reached from tail commits - skip: ancestors of commits in both 'keep' and 'drop' Commits in 'keep' and/or 'drop' may be added later to the 'skip' set if we discover later that they are part of a common subgraph of the head and tail commits. From these sets we can calculate the commits we are interested in: lca commits are those in 'keep' and 'drop', but not in 'skip'. findtwixt commits are those in 'keep', but not in 'drop' or 'skip'. The "LCA" commit returned is a common ancestor such that there are no other common ancestors that can reach that commit. Although there can be multiple commits that meet this criteria, where one is technically lower on the commit-graph than the other, these cases only happen in complex merge arrangements and any choice is likely a decent merge base. Repainting is now done in paint() directly. When we find a boundary commit, we switch our paint color to 'skip'. 'skip' painting does not stop when it hits another color; we continue until we are left with only 'skip' commits on the queue. This fixes several mishandled cases in the current algorithm: 1. If we hit the common subgraph from tail commits first (if the tail commit was newer than the head commit), we ended up traversing the entire commit graph. This is because we couldn't distinguish between 'drop' commits that were part of the common subgraph, and those that were still looking for it. 2. If we traversed through an initial part of the common subgraph from head commits before reaching it from tail commits, these commits were returned from findtwixt even though they were also reachable from tail commits. 3. In the same case as 2, we might end up choosing an incorrect commit as the LCA, which is an ancestor of the real LCA.
This commit is contained in:
Michael Forney
parent
873f381e29
commit
2e47badb88
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@ -160,14 +160,12 @@ struct Qelt {
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Object *o;
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vlong mtime;
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int color;
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int dist;
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};
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struct Objq {
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Qelt *heap;
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int nheap;
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int heapsz;
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int nkeep;
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};
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struct Dtab {
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@ -324,5 +322,5 @@ void closeconn(Conn *);
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/* queues */
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void qinit(Objq*);
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void qclear(Objq*);
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void qput(Objq*, Object*, int, int);
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void qput(Objq*, Object*, int);
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int qpop(Objq*, Qelt*);
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@ -205,7 +205,7 @@ showcommits(char *c)
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sysfatal("load %H: %r", h);
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qinit(&objq);
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osinit(&done);
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qput(&objq, o, 0, 0);
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qput(&objq, o, 0);
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while(qpop(&objq, &e)){
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show(e.o);
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for(i = 0; i < e.o->commit->nparent; i++){
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@ -214,7 +214,7 @@ showcommits(char *c)
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if((p = readobject(e.o->commit->parent[i])) == nil)
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sysfatal("load %H: %r", o->commit->parent[i]);
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osadd(&done, p);
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qput(&objq, p, 0, 0);
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qput(&objq, p, 0);
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}
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unref(e.o);
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}
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@ -5,25 +5,12 @@
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#include "git.h"
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typedef struct Eval Eval;
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typedef struct Lcaq Lcaq;
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struct Lcaq {
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Objq;
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Hash *head;
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Hash *tail;
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int nhead;
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int ntail;
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Object *best;
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int dist;
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};
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enum {
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Blank,
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Keep,
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Drop,
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Skip,
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};
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struct Eval {
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@ -38,6 +25,7 @@ static char *colors[] = {
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[Keep] "keep",
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[Drop] "drop",
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[Blank] "blank",
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[Skip] "skip",
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};
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static Object zcommit = {
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@ -113,97 +101,20 @@ take(Eval *ev, char *m)
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return 1;
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}
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static int
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pickbest(Lcaq *q, Qelt *e, int color)
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{
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int i, best, exact;
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best = 0;
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exact = 0;
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if(color == Blank || e->color == color)
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return 0;
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if(e->dist < q->dist){
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dprint(1, "found best (dist %d < %d): %H\n", e->dist, q->dist, e->o->hash);
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best = 1;
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}
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for(i = 0; i < q->nhead; i++)
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if(hasheq(&q->head[i], &e->o->hash)){
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dprint(1, "found best (exact head): %H\n", e->o->hash);
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best = 1;
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exact = 1;
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}
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for(i = 0; i < q->ntail; i++)
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if(hasheq(&q->tail[i], &e->o->hash)){
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dprint(1, "found best (exact tail): %H\n", e->o->hash);
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best = 1;
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exact = 1;
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}
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if(best){
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q->best = e->o;
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q->dist = e->dist;
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}
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return exact;
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}
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static int
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repaint(Lcaq *lcaq, Objset *keep, Objset *drop, Object *o, int dist, int ancestor)
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{
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Lcaq objq;
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Qelt e;
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Object *p;
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int i;
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qinit(&objq);
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if((o = readobject(o->hash)) == nil)
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return -1;
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qput(&objq, o, Drop, dist);
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while(qpop(&objq, &e)){
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o = e.o;
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if(oshas(drop, o->hash))
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continue;
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if(ancestor && pickbest(lcaq, &e, Keep))
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goto out;
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if(!oshas(keep, o->hash)){
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dprint(2, "repaint: blank => drop %H\n", o->hash);
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osadd(drop, o);
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continue;
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}
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for(i = 0; i < o->commit->nparent; i++){
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if(oshas(drop, o->commit->parent[i]))
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continue;
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if((p = readobject(o->commit->parent[i])) == nil)
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goto out;
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if(p->type != GCommit){
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fprint(2, "hash %H not commit\n", p->hash);
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unref(p);
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}
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qput(&objq, p, Drop, e.dist+1);
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}
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unref(e.o);
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}
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out:
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qclear(&objq);
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return 0;
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}
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static int
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paint(Hash *head, int nhead, Hash *tail, int ntail, Object ***res, int *nres, int ancestor)
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{
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Qelt e;
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Lcaq objq;
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Objset keep, drop;
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Objq objq;
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Objset keep, drop, skip;
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Object *o, *c;
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int i, ncolor;
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int i, nskip;
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osinit(&keep);
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osinit(&drop);
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memset(&objq, 0, sizeof(objq));
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osinit(&skip);
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qinit(&objq);
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objq.head = head;
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objq.nhead = nhead;
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objq.tail = tail;
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objq.ntail = ntail;
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objq.dist = 1<<30;
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nskip = 0;
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for(i = 0; i < nhead; i++){
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if((o = readobject(head[i])) == nil){
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@ -217,7 +128,7 @@ paint(Hash *head, int nhead, Hash *tail, int ntail, Object ***res, int *nres, in
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continue;
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}
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dprint(1, "init: keep %H\n", o->hash);
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qput(&objq, o, Keep, 0);
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qput(&objq, o, Keep);
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unref(o);
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}
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for(i = 0; i < ntail; i++){
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@ -231,70 +142,83 @@ paint(Hash *head, int nhead, Hash *tail, int ntail, Object ***res, int *nres, in
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continue;
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}
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dprint(1, "init: drop %H\n", o->hash);
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qput(&objq, o, Drop, 0);
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qput(&objq, o, Drop);
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unref(o);
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}
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dprint(1, "finding twixt commits\n");
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while(qpop(&objq, &e)){
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if(oshas(&drop, e.o->hash))
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ncolor = Drop;
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else if(oshas(&keep, e.o->hash))
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ncolor = Keep;
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else
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ncolor = Blank;
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if(ancestor && pickbest(&objq, &e, ncolor))
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goto exactlca;
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if(ncolor == Keep && e.color == Keep || ncolor == Drop)
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while(nskip != objq.nheap && qpop(&objq, &e)){
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if(e.color == Skip)
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nskip--;
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if(oshas(&skip, e.o->hash))
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continue;
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if(ncolor == Keep && e.color == Drop){
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if(repaint(&objq, &keep, &drop, e.o, e.dist, ancestor) == -1)
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goto error;
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}else if (ncolor == Blank) {
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if(e.color == Keep)
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osadd(&keep, e.o);
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else
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osadd(&drop, e.o);
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o = readobject(e.o->hash);
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for(i = 0; i < o->commit->nparent; i++){
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if((c = readobject(e.o->commit->parent[i])) == nil)
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goto error;
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if(c->type != GCommit){
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fprint(2, "warning: %H does not point at commit\n", c->hash);
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unref(c);
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continue;
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}
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dprint(2, "\tenqueue: %s %H\n", colors[e.color], c->hash);
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qput(&objq, c, e.color, e.dist+1);
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unref(c);
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}
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unref(o);
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switch(e.color){
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case Keep:
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if(oshas(&keep, e.o->hash))
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continue;
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if(oshas(&drop, e.o->hash))
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e.color = Skip;
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osadd(&keep, e.o);
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break;
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case Drop:
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if(oshas(&drop, e.o->hash))
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continue;
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if(oshas(&keep, e.o->hash))
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e.color = Skip;
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osadd(&drop, e.o);
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break;
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case Skip:
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osadd(&skip, e.o);
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break;
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}
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o = readobject(e.o->hash);
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for(i = 0; i < o->commit->nparent; i++){
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if((c = readobject(e.o->commit->parent[i])) == nil)
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goto error;
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if(c->type != GCommit){
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fprint(2, "warning: %H does not point at commit\n", c->hash);
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unref(c);
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continue;
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}
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dprint(2, "\tenqueue: %s %H\n", colors[e.color], c->hash);
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qput(&objq, c, e.color);
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unref(c);
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if(e.color == Skip)
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nskip++;
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}
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unref(o);
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}
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exactlca:
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if(ancestor){
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dprint(1, "found ancestor\n");
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if(objq.best == nil){
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o = nil;
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for(i = 0; i < keep.sz; i++){
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o = keep.obj[i];
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if(o != nil && oshas(&drop, o->hash) && !oshas(&skip, o->hash))
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break;
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}
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if(i == keep.sz){
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*nres = 0;
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*res = nil;
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}else{
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*nres = 1;
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*res = eamalloc(1, sizeof(Object*));
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(*res)[0] = objq.best;
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(*res)[0] = o;
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}
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}else{
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dprint(1, "found twixt\n");
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*res = eamalloc(keep.nobj, sizeof(Object*));
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*nres = 0;
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for(i = 0; i < keep.sz; i++){
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if(keep.obj[i] != nil && !oshas(&drop, keep.obj[i]->hash)){
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(*res)[*nres] = keep.obj[i];
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o = keep.obj[i];
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if(o != nil && !oshas(&drop, o->hash) && !oshas(&skip, o->hash)){
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(*res)[*nres] = o;
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(*nres)++;
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}
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}
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}
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osclear(&keep);
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osclear(&drop);
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osclear(&skip);
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return 0;
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error:
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dprint(1, "twixt error: %r\n");
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@ -338,7 +338,7 @@ qclear(Objq *q)
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}
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void
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qput(Objq *q, Object *o, int color, int dist)
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qput(Objq *q, Object *o, int color)
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{
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Qelt t;
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int i;
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@ -349,7 +349,6 @@ qput(Objq *q, Object *o, int color, int dist)
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}
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q->heap[q->nheap].o = o;
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q->heap[q->nheap].color = color;
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q->heap[q->nheap].dist = dist;
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q->heap[q->nheap].mtime = o->commit->mtime;
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for(i = q->nheap; i > 0; i = (i-1)/2){
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if(q->heap[i].mtime < q->heap[(i-1)/2].mtime)
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