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9f36c7f497
In case you're wondering, the gcc-2.7.2.1 import uses this to generate code. The size of the generated code is bigger than the entire bison release, making this a saving. The bison doc is pretty good apparently.
138 lines
4.6 KiB
C
138 lines
4.6 KiB
C
/* Type definitions for nondeterministic finite state machine 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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/* These type definitions are used to represent a nondeterministic
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finite state machine that parses the specified grammar.
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This information is generated by the function generate_states
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in the file LR0.
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Each state of the machine is described by a set of items --
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particular positions in particular rules -- that are the possible
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places where parsing could continue when the machine is in this state.
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These symbols at these items are the allowable inputs that can follow now.
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A core represents one state. States are numbered in the number field.
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When generate_states is finished, the starting state is state 0
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and nstates is the number of states. (A transition to a state
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whose state number is nstates indicates termination.) All the cores
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are chained together and first_state points to the first one (state 0).
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For each state there is a particular symbol which must have been the
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last thing accepted to reach that state. It is the accessing_symbol
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of the core.
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Each core contains a vector of nitems items which are the indices
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in the ritems vector of the items that are selected in this state.
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The link field is used for chaining buckets that hash states by
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their itemsets. This is for recognizing equivalent states and
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combining them when the states are generated.
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The two types of transitions are shifts (push the lookahead token
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and read another) and reductions (combine the last n things on the
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stack via a rule, replace them with the symbol that the rule derives,
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and leave the lookahead token alone). When the states are generated,
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these transitions are represented in two other lists.
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Each shifts structure describes the possible shift transitions out
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of one state, the state whose number is in the number field.
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The shifts structures are linked through next and first_shift points to them.
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Each contains a vector of numbers of the states that shift transitions
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can go to. The accessing_symbol fields of those states' cores say what kind
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of input leads to them.
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A shift to state zero should be ignored. Conflict resolution
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deletes shifts by changing them to zero.
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Each reductions structure describes the possible reductions at the state
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whose number is in the number field. The data is a list of nreds rules,
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represented by their rule numbers. first_reduction points to the list
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of these structures.
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Conflict resolution can decide that certain tokens in certain
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states should explicitly be errors (for implementing %nonassoc).
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For each state, the tokens that are errors for this reason
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are recorded in an errs structure, which has the state number
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in its number field. The rest of the errs structure is full
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of token numbers.
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There is at least one shift transition present in state zero.
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It leads to a next-to-final state whose accessing_symbol is
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the grammar's start symbol. The next-to-final state has one shift
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to the final state, whose accessing_symbol is zero (end of input).
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The final state has one shift, which goes to the termination state
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(whose number is nstates-1).
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The reason for the extra state at the end is to placate the parser's
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strategy of making all decisions one token ahead of its actions. */
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typedef
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struct core
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{
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struct core *next;
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struct core *link;
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short number;
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short accessing_symbol;
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short nitems;
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short items[1];
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}
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core;
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typedef
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struct shifts
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{
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struct shifts *next;
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short number;
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short nshifts;
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short shifts[1];
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}
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shifts;
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typedef
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struct errs
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{
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short nerrs;
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short errs[1];
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}
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errs;
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typedef
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struct reductions
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{
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struct reductions *next;
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short number;
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short nreds;
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short rules[1];
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}
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reductions;
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extern int nstates;
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extern core *first_state;
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extern shifts *first_shift;
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extern reductions *first_reduction;
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