mirror of
https://github.com/python/cpython.git
synced 2024-12-11 18:53:56 +08:00
bd311d8e4e
mid 1990. Remove an untrue XXX comment.
700 lines
14 KiB
C
700 lines
14 KiB
C
/* Parser generator */
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/* For a description, see the comments at end of this file */
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#include "Python.h"
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#include "pgenheaders.h"
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#include "token.h"
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#include "node.h"
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#include "grammar.h"
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#include "metagrammar.h"
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#include "pgen.h"
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extern int Py_DebugFlag;
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extern int Py_IgnoreEnvironmentFlag; /* needed by Py_GETENV */
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/* PART ONE -- CONSTRUCT NFA -- Cf. Algorithm 3.2 from [Aho&Ullman 77] */
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typedef struct _nfaarc {
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int ar_label;
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int ar_arrow;
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} nfaarc;
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typedef struct _nfastate {
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int st_narcs;
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nfaarc *st_arc;
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} nfastate;
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typedef struct _nfa {
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int nf_type;
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char *nf_name;
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int nf_nstates;
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nfastate *nf_state;
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int nf_start, nf_finish;
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} nfa;
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/* Forward */
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static void compile_rhs(labellist *ll,
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nfa *nf, node *n, int *pa, int *pb);
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static void compile_alt(labellist *ll,
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nfa *nf, node *n, int *pa, int *pb);
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static void compile_item(labellist *ll,
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nfa *nf, node *n, int *pa, int *pb);
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static void compile_atom(labellist *ll,
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nfa *nf, node *n, int *pa, int *pb);
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static int
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addnfastate(nfa *nf)
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{
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nfastate *st;
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PyMem_RESIZE(nf->nf_state, nfastate, nf->nf_nstates + 1);
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if (nf->nf_state == NULL)
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Py_FatalError("out of mem");
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st = &nf->nf_state[nf->nf_nstates++];
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st->st_narcs = 0;
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st->st_arc = NULL;
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return st - nf->nf_state;
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}
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static void
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addnfaarc(nfa *nf, int from, int to, int lbl)
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{
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nfastate *st;
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nfaarc *ar;
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st = &nf->nf_state[from];
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PyMem_RESIZE(st->st_arc, nfaarc, st->st_narcs + 1);
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if (st->st_arc == NULL)
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Py_FatalError("out of mem");
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ar = &st->st_arc[st->st_narcs++];
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ar->ar_label = lbl;
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ar->ar_arrow = to;
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}
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static nfa *
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newnfa(char *name)
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{
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nfa *nf;
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static int type = NT_OFFSET; /* All types will be disjunct */
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nf = PyMem_NEW(nfa, 1);
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if (nf == NULL)
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Py_FatalError("no mem for new nfa");
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nf->nf_type = type++;
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nf->nf_name = name; /* XXX strdup(name) ??? */
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nf->nf_nstates = 0;
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nf->nf_state = NULL;
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nf->nf_start = nf->nf_finish = -1;
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return nf;
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}
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typedef struct _nfagrammar {
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int gr_nnfas;
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nfa **gr_nfa;
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labellist gr_ll;
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} nfagrammar;
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/* Forward */
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static void compile_rule(nfagrammar *gr, node *n);
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static nfagrammar *
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newnfagrammar(void)
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{
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nfagrammar *gr;
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gr = PyMem_NEW(nfagrammar, 1);
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if (gr == NULL)
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Py_FatalError("no mem for new nfa grammar");
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gr->gr_nnfas = 0;
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gr->gr_nfa = NULL;
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gr->gr_ll.ll_nlabels = 0;
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gr->gr_ll.ll_label = NULL;
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addlabel(&gr->gr_ll, ENDMARKER, "EMPTY");
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return gr;
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}
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static nfa *
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addnfa(nfagrammar *gr, char *name)
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{
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nfa *nf;
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nf = newnfa(name);
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PyMem_RESIZE(gr->gr_nfa, nfa *, gr->gr_nnfas + 1);
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if (gr->gr_nfa == NULL)
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Py_FatalError("out of mem");
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gr->gr_nfa[gr->gr_nnfas++] = nf;
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addlabel(&gr->gr_ll, NAME, nf->nf_name);
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return nf;
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}
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#ifdef Py_DEBUG
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static char REQNFMT[] = "metacompile: less than %d children\n";
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#define REQN(i, count) \
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if (i < count) { \
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fprintf(stderr, REQNFMT, count); \
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Py_FatalError("REQN"); \
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} else
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#else
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#define REQN(i, count) /* empty */
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#endif
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static nfagrammar *
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metacompile(node *n)
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{
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nfagrammar *gr;
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int i;
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if (Py_DebugFlag)
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printf("Compiling (meta-) parse tree into NFA grammar\n");
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gr = newnfagrammar();
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REQ(n, MSTART);
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i = n->n_nchildren - 1; /* Last child is ENDMARKER */
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n = n->n_child;
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for (; --i >= 0; n++) {
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if (n->n_type != NEWLINE)
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compile_rule(gr, n);
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}
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return gr;
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}
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static void
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compile_rule(nfagrammar *gr, node *n)
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{
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nfa *nf;
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REQ(n, RULE);
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REQN(n->n_nchildren, 4);
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n = n->n_child;
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REQ(n, NAME);
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nf = addnfa(gr, n->n_str);
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n++;
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REQ(n, COLON);
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n++;
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REQ(n, RHS);
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compile_rhs(&gr->gr_ll, nf, n, &nf->nf_start, &nf->nf_finish);
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n++;
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REQ(n, NEWLINE);
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}
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static void
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compile_rhs(labellist *ll, nfa *nf, node *n, int *pa, int *pb)
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{
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int i;
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int a, b;
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REQ(n, RHS);
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i = n->n_nchildren;
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REQN(i, 1);
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n = n->n_child;
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REQ(n, ALT);
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compile_alt(ll, nf, n, pa, pb);
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if (--i <= 0)
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return;
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n++;
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a = *pa;
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b = *pb;
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*pa = addnfastate(nf);
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*pb = addnfastate(nf);
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addnfaarc(nf, *pa, a, EMPTY);
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addnfaarc(nf, b, *pb, EMPTY);
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for (; --i >= 0; n++) {
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REQ(n, VBAR);
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REQN(i, 1);
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--i;
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n++;
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REQ(n, ALT);
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compile_alt(ll, nf, n, &a, &b);
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addnfaarc(nf, *pa, a, EMPTY);
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addnfaarc(nf, b, *pb, EMPTY);
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}
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}
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static void
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compile_alt(labellist *ll, nfa *nf, node *n, int *pa, int *pb)
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{
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int i;
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int a, b;
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REQ(n, ALT);
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i = n->n_nchildren;
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REQN(i, 1);
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n = n->n_child;
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REQ(n, ITEM);
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compile_item(ll, nf, n, pa, pb);
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--i;
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n++;
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for (; --i >= 0; n++) {
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REQ(n, ITEM);
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compile_item(ll, nf, n, &a, &b);
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addnfaarc(nf, *pb, a, EMPTY);
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*pb = b;
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}
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}
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static void
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compile_item(labellist *ll, nfa *nf, node *n, int *pa, int *pb)
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{
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int i;
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int a, b;
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REQ(n, ITEM);
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i = n->n_nchildren;
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REQN(i, 1);
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n = n->n_child;
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if (n->n_type == LSQB) {
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REQN(i, 3);
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n++;
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REQ(n, RHS);
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*pa = addnfastate(nf);
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*pb = addnfastate(nf);
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addnfaarc(nf, *pa, *pb, EMPTY);
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compile_rhs(ll, nf, n, &a, &b);
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addnfaarc(nf, *pa, a, EMPTY);
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addnfaarc(nf, b, *pb, EMPTY);
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REQN(i, 1);
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n++;
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REQ(n, RSQB);
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}
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else {
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compile_atom(ll, nf, n, pa, pb);
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if (--i <= 0)
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return;
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n++;
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addnfaarc(nf, *pb, *pa, EMPTY);
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if (n->n_type == STAR)
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*pb = *pa;
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else
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REQ(n, PLUS);
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}
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}
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static void
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compile_atom(labellist *ll, nfa *nf, node *n, int *pa, int *pb)
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{
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int i;
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REQ(n, ATOM);
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i = n->n_nchildren;
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REQN(i, 1);
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n = n->n_child;
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if (n->n_type == LPAR) {
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REQN(i, 3);
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n++;
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REQ(n, RHS);
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compile_rhs(ll, nf, n, pa, pb);
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n++;
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REQ(n, RPAR);
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}
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else if (n->n_type == NAME || n->n_type == STRING) {
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*pa = addnfastate(nf);
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*pb = addnfastate(nf);
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addnfaarc(nf, *pa, *pb, addlabel(ll, n->n_type, n->n_str));
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}
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else
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REQ(n, NAME);
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}
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static void
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dumpstate(labellist *ll, nfa *nf, int istate)
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{
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nfastate *st;
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int i;
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nfaarc *ar;
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printf("%c%2d%c",
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istate == nf->nf_start ? '*' : ' ',
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istate,
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istate == nf->nf_finish ? '.' : ' ');
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st = &nf->nf_state[istate];
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ar = st->st_arc;
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for (i = 0; i < st->st_narcs; i++) {
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if (i > 0)
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printf("\n ");
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printf("-> %2d %s", ar->ar_arrow,
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PyGrammar_LabelRepr(&ll->ll_label[ar->ar_label]));
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ar++;
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}
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printf("\n");
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}
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static void
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dumpnfa(labellist *ll, nfa *nf)
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{
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int i;
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printf("NFA '%s' has %d states; start %d, finish %d\n",
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nf->nf_name, nf->nf_nstates, nf->nf_start, nf->nf_finish);
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for (i = 0; i < nf->nf_nstates; i++)
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dumpstate(ll, nf, i);
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}
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/* PART TWO -- CONSTRUCT DFA -- Algorithm 3.1 from [Aho&Ullman 77] */
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static void
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addclosure(bitset ss, nfa *nf, int istate)
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{
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if (addbit(ss, istate)) {
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nfastate *st = &nf->nf_state[istate];
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nfaarc *ar = st->st_arc;
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int i;
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for (i = st->st_narcs; --i >= 0; ) {
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if (ar->ar_label == EMPTY)
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addclosure(ss, nf, ar->ar_arrow);
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ar++;
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}
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}
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}
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typedef struct _ss_arc {
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bitset sa_bitset;
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int sa_arrow;
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int sa_label;
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} ss_arc;
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typedef struct _ss_state {
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bitset ss_ss;
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int ss_narcs;
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ss_arc *ss_arc;
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int ss_deleted;
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int ss_finish;
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int ss_rename;
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} ss_state;
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typedef struct _ss_dfa {
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int sd_nstates;
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ss_state *sd_state;
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} ss_dfa;
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/* Forward */
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static void printssdfa(int xx_nstates, ss_state *xx_state, int nbits,
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labellist *ll, char *msg);
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static void simplify(int xx_nstates, ss_state *xx_state);
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static void convert(dfa *d, int xx_nstates, ss_state *xx_state);
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static void
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makedfa(nfagrammar *gr, nfa *nf, dfa *d)
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{
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int nbits = nf->nf_nstates;
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bitset ss;
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int xx_nstates;
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ss_state *xx_state, *yy;
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ss_arc *zz;
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int istate, jstate, iarc, jarc, ibit;
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nfastate *st;
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nfaarc *ar;
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ss = newbitset(nbits);
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addclosure(ss, nf, nf->nf_start);
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xx_state = PyMem_NEW(ss_state, 1);
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if (xx_state == NULL)
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Py_FatalError("no mem for xx_state in makedfa");
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xx_nstates = 1;
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yy = &xx_state[0];
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yy->ss_ss = ss;
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yy->ss_narcs = 0;
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yy->ss_arc = NULL;
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yy->ss_deleted = 0;
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yy->ss_finish = testbit(ss, nf->nf_finish);
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if (yy->ss_finish)
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printf("Error: nonterminal '%s' may produce empty.\n",
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nf->nf_name);
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/* This algorithm is from a book written before
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the invention of structured programming... */
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/* For each unmarked state... */
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for (istate = 0; istate < xx_nstates; ++istate) {
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yy = &xx_state[istate];
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ss = yy->ss_ss;
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/* For all its states... */
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for (ibit = 0; ibit < nf->nf_nstates; ++ibit) {
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if (!testbit(ss, ibit))
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continue;
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st = &nf->nf_state[ibit];
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/* For all non-empty arcs from this state... */
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for (iarc = 0; iarc < st->st_narcs; iarc++) {
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ar = &st->st_arc[iarc];
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if (ar->ar_label == EMPTY)
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continue;
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/* Look up in list of arcs from this state */
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for (jarc = 0; jarc < yy->ss_narcs; ++jarc) {
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zz = &yy->ss_arc[jarc];
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if (ar->ar_label == zz->sa_label)
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goto found;
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}
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/* Add new arc for this state */
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PyMem_RESIZE(yy->ss_arc, ss_arc,
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yy->ss_narcs + 1);
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if (yy->ss_arc == NULL)
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Py_FatalError("out of mem");
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zz = &yy->ss_arc[yy->ss_narcs++];
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zz->sa_label = ar->ar_label;
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zz->sa_bitset = newbitset(nbits);
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zz->sa_arrow = -1;
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found: ;
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/* Add destination */
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addclosure(zz->sa_bitset, nf, ar->ar_arrow);
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}
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}
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/* Now look up all the arrow states */
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for (jarc = 0; jarc < xx_state[istate].ss_narcs; jarc++) {
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zz = &xx_state[istate].ss_arc[jarc];
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for (jstate = 0; jstate < xx_nstates; jstate++) {
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if (samebitset(zz->sa_bitset,
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xx_state[jstate].ss_ss, nbits)) {
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zz->sa_arrow = jstate;
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goto done;
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}
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}
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PyMem_RESIZE(xx_state, ss_state, xx_nstates + 1);
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if (xx_state == NULL)
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Py_FatalError("out of mem");
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zz->sa_arrow = xx_nstates;
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yy = &xx_state[xx_nstates++];
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yy->ss_ss = zz->sa_bitset;
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yy->ss_narcs = 0;
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yy->ss_arc = NULL;
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yy->ss_deleted = 0;
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yy->ss_finish = testbit(yy->ss_ss, nf->nf_finish);
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done: ;
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}
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}
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if (Py_DebugFlag)
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printssdfa(xx_nstates, xx_state, nbits, &gr->gr_ll,
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"before minimizing");
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simplify(xx_nstates, xx_state);
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if (Py_DebugFlag)
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printssdfa(xx_nstates, xx_state, nbits, &gr->gr_ll,
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"after minimizing");
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convert(d, xx_nstates, xx_state);
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/* XXX cleanup */
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}
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static void
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printssdfa(int xx_nstates, ss_state *xx_state, int nbits,
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labellist *ll, char *msg)
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{
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int i, ibit, iarc;
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ss_state *yy;
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ss_arc *zz;
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printf("Subset DFA %s\n", msg);
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for (i = 0; i < xx_nstates; i++) {
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yy = &xx_state[i];
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if (yy->ss_deleted)
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continue;
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printf(" Subset %d", i);
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if (yy->ss_finish)
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printf(" (finish)");
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printf(" { ");
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for (ibit = 0; ibit < nbits; ibit++) {
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if (testbit(yy->ss_ss, ibit))
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printf("%d ", ibit);
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}
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printf("}\n");
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for (iarc = 0; iarc < yy->ss_narcs; iarc++) {
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zz = &yy->ss_arc[iarc];
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printf(" Arc to state %d, label %s\n",
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zz->sa_arrow,
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PyGrammar_LabelRepr(
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&ll->ll_label[zz->sa_label]));
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}
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}
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}
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/* PART THREE -- SIMPLIFY DFA */
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/* Simplify the DFA by repeatedly eliminating states that are
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equivalent to another oner. This is NOT Algorithm 3.3 from
|
|
[Aho&Ullman 77]. It does not always finds the minimal DFA,
|
|
but it does usually make a much smaller one... (For an example
|
|
of sub-optimal behavior, try S: x a b+ | y a b+.)
|
|
*/
|
|
|
|
static int
|
|
samestate(ss_state *s1, ss_state *s2)
|
|
{
|
|
int i;
|
|
|
|
if (s1->ss_narcs != s2->ss_narcs || s1->ss_finish != s2->ss_finish)
|
|
return 0;
|
|
for (i = 0; i < s1->ss_narcs; i++) {
|
|
if (s1->ss_arc[i].sa_arrow != s2->ss_arc[i].sa_arrow ||
|
|
s1->ss_arc[i].sa_label != s2->ss_arc[i].sa_label)
|
|
return 0;
|
|
}
|
|
return 1;
|
|
}
|
|
|
|
static void
|
|
renamestates(int xx_nstates, ss_state *xx_state, int from, int to)
|
|
{
|
|
int i, j;
|
|
|
|
if (Py_DebugFlag)
|
|
printf("Rename state %d to %d.\n", from, to);
|
|
for (i = 0; i < xx_nstates; i++) {
|
|
if (xx_state[i].ss_deleted)
|
|
continue;
|
|
for (j = 0; j < xx_state[i].ss_narcs; j++) {
|
|
if (xx_state[i].ss_arc[j].sa_arrow == from)
|
|
xx_state[i].ss_arc[j].sa_arrow = to;
|
|
}
|
|
}
|
|
}
|
|
|
|
static void
|
|
simplify(int xx_nstates, ss_state *xx_state)
|
|
{
|
|
int changes;
|
|
int i, j;
|
|
|
|
do {
|
|
changes = 0;
|
|
for (i = 1; i < xx_nstates; i++) {
|
|
if (xx_state[i].ss_deleted)
|
|
continue;
|
|
for (j = 0; j < i; j++) {
|
|
if (xx_state[j].ss_deleted)
|
|
continue;
|
|
if (samestate(&xx_state[i], &xx_state[j])) {
|
|
xx_state[i].ss_deleted++;
|
|
renamestates(xx_nstates, xx_state,
|
|
i, j);
|
|
changes++;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
} while (changes);
|
|
}
|
|
|
|
|
|
/* PART FOUR -- GENERATE PARSING TABLES */
|
|
|
|
/* Convert the DFA into a grammar that can be used by our parser */
|
|
|
|
static void
|
|
convert(dfa *d, int xx_nstates, ss_state *xx_state)
|
|
{
|
|
int i, j;
|
|
ss_state *yy;
|
|
ss_arc *zz;
|
|
|
|
for (i = 0; i < xx_nstates; i++) {
|
|
yy = &xx_state[i];
|
|
if (yy->ss_deleted)
|
|
continue;
|
|
yy->ss_rename = addstate(d);
|
|
}
|
|
|
|
for (i = 0; i < xx_nstates; i++) {
|
|
yy = &xx_state[i];
|
|
if (yy->ss_deleted)
|
|
continue;
|
|
for (j = 0; j < yy->ss_narcs; j++) {
|
|
zz = &yy->ss_arc[j];
|
|
addarc(d, yy->ss_rename,
|
|
xx_state[zz->sa_arrow].ss_rename,
|
|
zz->sa_label);
|
|
}
|
|
if (yy->ss_finish)
|
|
addarc(d, yy->ss_rename, yy->ss_rename, 0);
|
|
}
|
|
|
|
d->d_initial = 0;
|
|
}
|
|
|
|
|
|
/* PART FIVE -- GLUE IT ALL TOGETHER */
|
|
|
|
static grammar *
|
|
maketables(nfagrammar *gr)
|
|
{
|
|
int i;
|
|
nfa *nf;
|
|
dfa *d;
|
|
grammar *g;
|
|
|
|
if (gr->gr_nnfas == 0)
|
|
return NULL;
|
|
g = newgrammar(gr->gr_nfa[0]->nf_type);
|
|
/* XXX first rule must be start rule */
|
|
g->g_ll = gr->gr_ll;
|
|
|
|
for (i = 0; i < gr->gr_nnfas; i++) {
|
|
nf = gr->gr_nfa[i];
|
|
if (Py_DebugFlag) {
|
|
printf("Dump of NFA for '%s' ...\n", nf->nf_name);
|
|
dumpnfa(&gr->gr_ll, nf);
|
|
printf("Making DFA for '%s' ...\n", nf->nf_name);
|
|
}
|
|
d = adddfa(g, nf->nf_type, nf->nf_name);
|
|
makedfa(gr, gr->gr_nfa[i], d);
|
|
}
|
|
|
|
return g;
|
|
}
|
|
|
|
grammar *
|
|
pgen(node *n)
|
|
{
|
|
nfagrammar *gr;
|
|
grammar *g;
|
|
|
|
gr = metacompile(n);
|
|
g = maketables(gr);
|
|
translatelabels(g);
|
|
addfirstsets(g);
|
|
return g;
|
|
}
|
|
|
|
grammar *
|
|
Py_pgen(node *n)
|
|
{
|
|
return pgen(n);
|
|
}
|
|
|
|
/*
|
|
|
|
Description
|
|
-----------
|
|
|
|
Input is a grammar in extended BNF (using * for repetition, + for
|
|
at-least-once repetition, [] for optional parts, | for alternatives and
|
|
() for grouping). This has already been parsed and turned into a parse
|
|
tree.
|
|
|
|
Each rule is considered as a regular expression in its own right.
|
|
It is turned into a Non-deterministic Finite Automaton (NFA), which
|
|
is then turned into a Deterministic Finite Automaton (DFA), which is then
|
|
optimized to reduce the number of states. See [Aho&Ullman 77] chapter 3,
|
|
or similar compiler books (this technique is more often used for lexical
|
|
analyzers).
|
|
|
|
The DFA's are used by the parser as parsing tables in a special way
|
|
that's probably unique. Before they are usable, the FIRST sets of all
|
|
non-terminals are computed.
|
|
|
|
Reference
|
|
---------
|
|
|
|
[Aho&Ullman 77]
|
|
Aho&Ullman, Principles of Compiler Design, Addison-Wesley 1977
|
|
(first edition)
|
|
|
|
*/
|