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Richard M. Stallman
351
src/closure.c
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351
src/closure.c
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/* Subroutines for bison
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Copyright (C) 1984, 1989 Free Software Foundation, Inc.
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This file is part of Bison, the GNU Compiler Compiler.
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Bison is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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Bison is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with Bison; see the file COPYING. If not, write to
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the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
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/* subroutines of file LR0.c.
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Entry points:
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closure (items, n)
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Given a vector of item numbers items, of length n,
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set up ruleset and itemset to indicate what rules could be run
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and which items could be accepted when those items are the active ones.
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ruleset contains a bit for each rule. closure sets the bits
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for all rules which could potentially describe the next input to be read.
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itemset is a vector of item numbers; itemsetend points to just beyond the end
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of the part of it that is significant.
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closure places there the indices of all items which represent units of
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input that could arrive next.
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initialize_closure (n)
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Allocates the itemset and ruleset vectors,
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and precomputes useful data so that closure can be called.
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n is the number of elements to allocate for itemset.
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finalize_closure ()
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Frees itemset, ruleset and internal data.
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*/
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#include <stdio.h>
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#include "system.h"
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#include "machine.h"
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#include "new.h"
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#include "gram.h"
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extern short **derives;
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extern char **tags;
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void set_fderives();
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void set_firsts();
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extern void RTC();
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short *itemset;
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short *itemsetend;
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static unsigned *ruleset;
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/* internal data. See comments before set_fderives and set_firsts. */
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static unsigned *fderives;
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static unsigned *firsts;
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/* number of words required to hold a bit for each rule */
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static int rulesetsize;
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/* number of words required to hold a bit for each variable */
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static int varsetsize;
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void
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initialize_closure(n)
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int n;
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{
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itemset = NEW2(n, short);
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rulesetsize = WORDSIZE(nrules + 1);
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ruleset = NEW2(rulesetsize, unsigned);
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set_fderives();
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}
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/* set fderives to an nvars by nrules matrix of bits
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indicating which rules can help derive the beginning of the data
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for each nonterminal. For example, if symbol 5 can be derived as
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the sequence of symbols 8 3 20, and one of the rules for deriving
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symbol 8 is rule 4, then the [5 - ntokens, 4] bit in fderives is set. */
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void
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set_fderives()
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{
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register unsigned *rrow;
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register unsigned *vrow;
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register int j;
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register unsigned cword;
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register short *rp;
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register int b;
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int ruleno;
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int i;
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fderives = NEW2(nvars * rulesetsize, unsigned) - ntokens * rulesetsize;
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set_firsts();
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rrow = fderives + ntokens * rulesetsize;
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for (i = ntokens; i < nsyms; i++)
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{
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vrow = firsts + ((i - ntokens) * varsetsize);
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cword = *vrow++;
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b = 0;
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for (j = ntokens; j < nsyms; j++)
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{
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if (cword & (1 << b))
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{
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rp = derives[j];
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while ((ruleno = *rp++) > 0)
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{
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SETBIT(rrow, ruleno);
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}
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}
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b++;
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if (b >= BITS_PER_WORD && j + 1 < nsyms)
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{
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cword = *vrow++;
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b = 0;
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}
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}
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rrow += rulesetsize;
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}
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#ifdef DEBUG
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print_fderives();
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#endif
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FREE(firsts);
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}
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/* set firsts to be an nvars by nvars bit matrix indicating which items
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can represent the beginning of the input corresponding to which other items.
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For example, if some rule expands symbol 5 into the sequence of symbols 8 3 20,
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the symbol 8 can be the beginning of the data for symbol 5,
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so the bit [8 - ntokens, 5 - ntokens] in firsts is set. */
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void
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set_firsts()
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{
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register unsigned *row;
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/* register int done; JF unused */
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register int symbol;
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register short *sp;
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register int rowsize;
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int i;
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varsetsize = rowsize = WORDSIZE(nvars);
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firsts = NEW2(nvars * rowsize, unsigned);
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row = firsts;
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for (i = ntokens; i < nsyms; i++)
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{
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sp = derives[i];
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while (*sp >= 0)
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{
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symbol = ritem[rrhs[*sp++]];
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if (ISVAR(symbol))
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{
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symbol -= ntokens;
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SETBIT(row, symbol);
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}
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}
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row += rowsize;
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}
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RTC(firsts, nvars);
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#ifdef DEBUG
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print_firsts();
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#endif
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}
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void
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closure(core, n)
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short *core;
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int n;
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{
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register int ruleno;
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register unsigned word;
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register short *csp;
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register unsigned *dsp;
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register unsigned *rsp;
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short *csend;
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unsigned *rsend;
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int symbol;
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int itemno;
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rsp = ruleset;
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rsend = ruleset + rulesetsize;
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csend = core + n;
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if (n == 0)
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{
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dsp = fderives + start_symbol * rulesetsize;
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while (rsp < rsend)
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*rsp++ = *dsp++;
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}
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else
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{
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while (rsp < rsend)
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*rsp++ = 0;
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csp = core;
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while (csp < csend)
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{
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symbol = ritem[*csp++];
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if (ISVAR(symbol))
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{
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dsp = fderives + symbol * rulesetsize;
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rsp = ruleset;
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while (rsp < rsend)
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*rsp++ |= *dsp++;
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}
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}
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}
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ruleno = 0;
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itemsetend = itemset;
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csp = core;
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rsp = ruleset;
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while (rsp < rsend)
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{
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word = *rsp++;
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if (word == 0)
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{
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ruleno += BITS_PER_WORD;
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}
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else
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{
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register int b;
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for (b = 0; b < BITS_PER_WORD; b++)
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{
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if (word & (1 << b))
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{
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itemno = rrhs[ruleno];
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while (csp < csend && *csp < itemno)
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*itemsetend++ = *csp++;
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*itemsetend++ = itemno;
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}
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ruleno++;
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}
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}
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}
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while (csp < csend)
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*itemsetend++ = *csp++;
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#ifdef DEBUG
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print_closure(n);
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#endif
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}
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void
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finalize_closure()
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{
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FREE(itemset);
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FREE(ruleset);
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FREE(fderives + ntokens * rulesetsize);
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}
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#ifdef DEBUG
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print_closure(n)
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int n;
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{
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register short *isp;
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printf("\n\nn = %d\n\n", n);
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for (isp = itemset; isp < itemsetend; isp++)
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printf(" %d\n", *isp);
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}
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print_firsts()
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{
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register int i;
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register int j;
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register unsigned *rowp;
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printf("\n\n\nFIRSTS\n\n");
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for (i = ntokens; i < nsyms; i++)
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{
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printf("\n\n%s firsts\n\n", tags[i]);
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rowp = firsts + ((i - ntokens) * varsetsize);
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for (j = 0; j < nvars; j++)
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if (BITISSET (rowp, j))
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printf(" %s\n", tags[j + ntokens]);
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}
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}
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print_fderives()
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{
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register int i;
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register int j;
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register unsigned *rp;
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printf("\n\n\nFDERIVES\n");
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for (i = ntokens; i < nsyms; i++)
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{
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printf("\n\n%s derives\n\n", tags[i]);
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rp = fderives + i * rulesetsize;
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for (j = 0; j <= nrules; j++)
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if (BITISSET (rp, j))
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printf(" %d\n", j);
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}
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fflush(stdout);
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}
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#endif
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