diff options
Diffstat (limited to 'generic/regc_nfa.c')
| -rw-r--r-- | generic/regc_nfa.c | 349 |
1 files changed, 258 insertions, 91 deletions
diff --git a/generic/regc_nfa.c b/generic/regc_nfa.c index 459968a..11fd49b 100644 --- a/generic/regc_nfa.c +++ b/generic/regc_nfa.c @@ -460,6 +460,42 @@ struct arc *victim; } /* + - nonemptyouts - count non-EMPTY out arcs of a state + ^ static int nonemptyouts(struct state *); + */ +static int +nonemptyouts(s) +struct state *s; +{ + int n = 0; + struct arc *a; + + for (a = s->outs; a != NULL; a = a->outchain) { + if (a->type != EMPTY) + n++; + } + return n; +} + +/* + - nonemptyins - count non-EMPTY in arcs of a state + ^ static int nonemptyins(struct state *); + */ +static int +nonemptyins(s) +struct state *s; +{ + int n = 0; + struct arc *a; + + for (a = s->ins; a != NULL; a = a->inchain) { + if (a->type != EMPTY) + n++; + } + return n; +} + +/* - findarc - find arc, if any, from given source with given type and color * If there is more than one such arc, the result is random. ^ static struct arc *findarc(struct state *, int, pcolor); @@ -538,6 +574,26 @@ struct state *new; } /* + - copynonemptyins - as above, but ignore empty arcs + ^ static void copynonemptyins(struct nfa *, struct state *, struct state *); + */ +static VOID +copynonemptyins(nfa, oldState, newState) +struct nfa *nfa; +struct state *oldState; +struct state *newState; +{ + struct arc *a; + + assert(oldState != newState); + + for (a=oldState->ins ; a!=NULL ; a=a->inchain) { + if (a->type != EMPTY) + cparc(nfa, a, a->from, newState); + } +} + +/* - moveouts - move all out arcs of a state to another state ^ static VOID moveouts(struct nfa *, struct state *, struct state *); */ @@ -574,6 +630,26 @@ struct state *new; for (a = old->outs; a != NULL; a = a->outchain) cparc(nfa, a, new, a->to); } + +/* + - copynonemptyouts - as above, but ignore empty arcs + ^ static void copynonemptyouts(struct nfa *, struct state *, struct state *); + */ +static VOID +copynonemptyouts(nfa, oldState, newState) +struct nfa *nfa; +struct state *oldState; +struct state *newState; +{ + struct arc *a; + + assert(oldState != newState); + + for (a=oldState->outs ; a!=NULL ; a=a->outchain) { + if (a->type != EMPTY) + cparc(nfa, a, newState, a->to); + } +} /* - cloneouts - copy out arcs of a state to another state pair, modifying type @@ -1137,103 +1213,194 @@ fixempties(nfa, f) struct nfa *nfa; FILE *f; /* for debug output; NULL none */ { - struct state *s; - struct state *nexts; - struct state *to; - struct arc *a; - struct arc *nexta; - int progress; - - /* find and eliminate empties until there are no more */ - do { - progress = 0; - for (s = nfa->states; s != NULL && !NISERR(); s = nexts) { - nexts = s->next; - for (a = s->outs; a != NULL && !NISERR(); - a = a->outchain) - if (a->type == EMPTY) - /* Mark a for deletion; copy arcs - * to preserve graph connectivity - * after it is gone. */ - unempty(nfa, a); - - /* Now pass through and delete the marked arcs. - * Doing all the deletion after all the marking - * prevents arc copying from resurrecting deleted - * arcs which can cause failure to converge. - * [Tcl Bug 3604074] */ - for (a = s->outs; a != NULL; a = nexta) { - nexta = a->outchain; - if (a->from == NULL) { - progress = 1; - to = a->to; - a->from = s; - freearc(nfa, a); - if (to->nins == 0) { - while ((a = to->outs)) - freearc(nfa, a); - if (nexts == to) - nexts = to->next; - freestate(nfa, to); - } - if (s->nouts == 0) { - while ((a = s->ins)) - freearc(nfa, a); - freestate(nfa, s); - } - } - } - } - if (progress && f != NULL) - dumpnfa(nfa, f); - } while (progress && !NISERR()); + struct state *s; + struct state *s2; + struct state *nexts; + struct arc *a; + struct arc *nexta; + + /* + * First, get rid of any states whose sole out-arc is an EMPTY, since + * they're basically just aliases for their successor. The parsing + * algorithm creates enough of these that it's worth special-casing this. + */ + for (s = nfa->states; s != NULL && !NISERR(); s = nexts) { + nexts = s->next; + if (s->nouts == 1 && !s->flag) { + a = s->outs; + assert(a != NULL && a->outchain == NULL); + if (a->type == EMPTY) { + if (s != a->to) + moveins(nfa, s, a->to); + dropstate(nfa, s); + } + } + } + + /* + * Similarly, get rid of any state with a single EMPTY in-arc, by folding + * it into its predecessor. + */ + for (s = nfa->states; s != NULL && !NISERR(); s = nexts) { + nexts = s->next; + /* while we're at it, ensure tmp fields are clear for next step */ + s->tmp = NULL; + if (s->nins == 1 && !s->flag) { + a = s->ins; + assert(a != NULL && a->inchain == NULL); + if (a->type == EMPTY) { + if (s != a->from) + moveouts(nfa, s, a->from); + dropstate(nfa, s); + } + } + } + + /* + * For each remaining NFA state, find all other states that are reachable + * from it by a chain of one or more EMPTY arcs. Then generate new arcs + * that eliminate the need for each such chain. + * + * If we just do this straightforwardly, the algorithm gets slow in + * complex graphs, because the same arcs get copied to all intermediate + * states of an EMPTY chain, and then uselessly pushed repeatedly to the + * chain's final state; we waste a lot of time in newarc's duplicate + * checking. To improve matters, we decree that any state with only EMPTY + * out-arcs is "doomed" and will not be part of the final NFA. That can be + * ensured by not adding any new out-arcs to such a state. Having ensured + * that, we need not update the state's in-arcs list either; all arcs that + * might have gotten pushed forward to it will just get pushed directly to + * successor states. This eliminates most of the useless duplicate arcs. + */ + for (s = nfa->states; s != NULL && !NISERR(); s = s->next) { + for (s2 = emptyreachable(s, s); s2 != s && !NISERR(); s2 = nexts) { + /* + * If s2 is doomed, we decide that (1) we will always push arcs + * forward to it, not pull them back to s; and (2) we can optimize + * away the push-forward, per comment above. So do nothing. + */ + if (s2->flag || nonemptyouts(s2) > 0) + replaceempty(nfa, s, s2); + + /* Reset the tmp fields as we walk back */ + nexts = s2->tmp; + s2->tmp = NULL; + } + s->tmp = NULL; + } + + /* + * Now remove all the EMPTY arcs, since we don't need them anymore. + */ + for (s = nfa->states; s != NULL && !NISERR(); s = s->next) { + for (a = s->outs; a != NULL; a = nexta) { + nexta = a->outchain; + if (a->type == EMPTY) + freearc(nfa, a); + } + } + + /* + * And remove any states that have become useless. (This cleanup is not + * very thorough, and would be even less so if we tried to combine it with + * the previous step; but cleanup() will take care of anything we miss.) + */ + for (s = nfa->states; s != NULL && !NISERR(); s = nexts) { + nexts = s->next; + if ((s->nins == 0 || s->nouts == 0) && !s->flag) + dropstate(nfa, s); + } + + if (f != NULL && !NISERR()) + dumpnfa(nfa, f); } - + /* - - unempty - optimize out an EMPTY arc, if possible - * Actually, as it stands this function always succeeds, but the return - * value is kept with an eye on possible future changes. - ^ static int unempty(struct nfa *, struct arc *); + - emptyreachable - recursively find all states reachable from s by EMPTY arcs + * The return value is the last such state found. Its tmp field links back + * to the next-to-last such state, and so on back to s, so that all these + * states can be located without searching the whole NFA. + * The maximum recursion depth here is equal to the length of the longest + * loop-free chain of EMPTY arcs, which is surely no more than the size of + * the NFA, and in practice will be a lot less than that. + ^ static struct state *emptyreachable(struct state *, struct state *); */ -static int /* 0 couldn't, 1 could */ -unempty(nfa, a) +static struct state * +emptyreachable(s, lastfound) +struct state *s; +struct state *lastfound; +{ + struct arc *a; + + s->tmp = lastfound; + lastfound = s; + for (a = s->outs; a != NULL; a = a->outchain) { + if (a->type == EMPTY && a->to->tmp == NULL) + lastfound = emptyreachable(a->to, lastfound); + } + return lastfound; +} + +/* + - replaceempty - replace an EMPTY arc chain with some non-empty arcs + * The EMPTY arc(s) should be deleted later, but we can't do it here because + * they may still be needed to identify other arc chains during fixempties(). + ^ static void replaceempty(struct nfa *, struct state *, struct state *); + */ +static VOID +replaceempty(nfa, from, to) struct nfa *nfa; -struct arc *a; +struct state *from; +struct state *to; { - struct state *from = a->from; - struct state *to = a->to; - - assert(a->type == EMPTY); - assert(from != nfa->pre && to != nfa->post); - - if (from == to) { /* vacuous loop */ - freearc(nfa, a); - return 1; - } - - /* Mark arc for deletion */ - a->from = NULL; - - if (from->nouts > to->nins) { - copyouts(nfa, to, from); - return 1; - } - if (from->nouts < to->nins) { - copyins(nfa, from, to); - return 1; - } - - /* from->nouts == to->nins */ - /* decide on secondary issue: move/copy fewest arcs */ - if (from->nins > to->nouts) { - copyouts(nfa, to, from); - return 1; - } - - copyins(nfa, from, to); - return 1; + int fromouts; + int toins; + + assert(from != to); + + /* + * Create replacement arcs that bypass the need for the EMPTY chain. We + * can do this either by pushing arcs forward (linking directly from + * "from"'s predecessors to "to") or by pulling them back (linking + * directly from "from" to "to"'s successors). In general, we choose + * whichever way creates greater fan-out or fan-in, so as to improve the + * odds of reducing the other state to zero in-arcs or out-arcs and + * thereby being able to delete it. However, if "from" is doomed (has no + * non-EMPTY out-arcs), we must keep it so, so always push forward in that + * case. + * + * The fan-out/fan-in comparison should count only non-EMPTY arcs. If + * "from" is doomed, we can skip counting "to"'s arcs, since we want to + * force taking the copynonemptyins path in that case. + */ + fromouts = nonemptyouts(from); + toins = (fromouts == 0) ? 1 : nonemptyins(to); + + if (fromouts > toins) { + copynonemptyouts(nfa, to, from); + return; + } + if (fromouts < toins) { + copynonemptyins(nfa, from, to); + return; + } + + /* + * fromouts == toins. Decide on secondary issue: copy fewest arcs. + * + * Doesn't seem to be worth the trouble to exclude empties from these + * comparisons; that takes extra time and doesn't seem to improve the + * resulting graph much. + */ + if (from->nins > to->nouts) { + copynonemptyouts(nfa, to, from); + return; + } else { + copynonemptyins(nfa, from, to); + return; + } } - + /* - cleanup - clean up NFA after optimizations ^ static VOID cleanup(struct nfa *); |