mirror of
https://git.FreeBSD.org/src.git
synced 2024-12-17 10:26:15 +00:00
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,
|
|
Copyright (C) 1984, 1989 Free Software Foundation, Inc.
|
|
|
|
This file is part of Bison, the GNU Compiler Compiler.
|
|
|
|
Bison is free software; you can redistribute it and/or modify
|
|
it under the terms of the GNU General Public License as published by
|
|
the Free Software Foundation; either version 2, or (at your option)
|
|
any later version.
|
|
|
|
Bison is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
GNU General Public License for more details.
|
|
|
|
You should have received a copy of the GNU General Public License
|
|
along with Bison; see the file COPYING. If not, write to
|
|
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
|
|
|
|
|
|
/* These type definitions are used to represent a nondeterministic
|
|
finite state machine that parses the specified grammar.
|
|
This information is generated by the function generate_states
|
|
in the file LR0.
|
|
|
|
Each state of the machine is described by a set of items --
|
|
particular positions in particular rules -- that are the possible
|
|
places where parsing could continue when the machine is in this state.
|
|
These symbols at these items are the allowable inputs that can follow now.
|
|
|
|
A core represents one state. States are numbered in the number field.
|
|
When generate_states is finished, the starting state is state 0
|
|
and nstates is the number of states. (A transition to a state
|
|
whose state number is nstates indicates termination.) All the cores
|
|
are chained together and first_state points to the first one (state 0).
|
|
|
|
For each state there is a particular symbol which must have been the
|
|
last thing accepted to reach that state. It is the accessing_symbol
|
|
of the core.
|
|
|
|
Each core contains a vector of nitems items which are the indices
|
|
in the ritems vector of the items that are selected in this state.
|
|
|
|
The link field is used for chaining buckets that hash states by
|
|
their itemsets. This is for recognizing equivalent states and
|
|
combining them when the states are generated.
|
|
|
|
The two types of transitions are shifts (push the lookahead token
|
|
and read another) and reductions (combine the last n things on the
|
|
stack via a rule, replace them with the symbol that the rule derives,
|
|
and leave the lookahead token alone). When the states are generated,
|
|
these transitions are represented in two other lists.
|
|
|
|
Each shifts structure describes the possible shift transitions out
|
|
of one state, the state whose number is in the number field.
|
|
The shifts structures are linked through next and first_shift points to them.
|
|
Each contains a vector of numbers of the states that shift transitions
|
|
can go to. The accessing_symbol fields of those states' cores say what kind
|
|
of input leads to them.
|
|
|
|
A shift to state zero should be ignored. Conflict resolution
|
|
deletes shifts by changing them to zero.
|
|
|
|
Each reductions structure describes the possible reductions at the state
|
|
whose number is in the number field. The data is a list of nreds rules,
|
|
represented by their rule numbers. first_reduction points to the list
|
|
of these structures.
|
|
|
|
Conflict resolution can decide that certain tokens in certain
|
|
states should explicitly be errors (for implementing %nonassoc).
|
|
For each state, the tokens that are errors for this reason
|
|
are recorded in an errs structure, which has the state number
|
|
in its number field. The rest of the errs structure is full
|
|
of token numbers.
|
|
|
|
There is at least one shift transition present in state zero.
|
|
It leads to a next-to-final state whose accessing_symbol is
|
|
the grammar's start symbol. The next-to-final state has one shift
|
|
to the final state, whose accessing_symbol is zero (end of input).
|
|
The final state has one shift, which goes to the termination state
|
|
(whose number is nstates-1).
|
|
The reason for the extra state at the end is to placate the parser's
|
|
strategy of making all decisions one token ahead of its actions. */
|
|
|
|
|
|
typedef
|
|
struct core
|
|
{
|
|
struct core *next;
|
|
struct core *link;
|
|
short number;
|
|
short accessing_symbol;
|
|
short nitems;
|
|
short items[1];
|
|
}
|
|
core;
|
|
|
|
|
|
|
|
typedef
|
|
struct shifts
|
|
{
|
|
struct shifts *next;
|
|
short number;
|
|
short nshifts;
|
|
short shifts[1];
|
|
}
|
|
shifts;
|
|
|
|
|
|
|
|
typedef
|
|
struct errs
|
|
{
|
|
short nerrs;
|
|
short errs[1];
|
|
}
|
|
errs;
|
|
|
|
|
|
|
|
typedef
|
|
struct reductions
|
|
{
|
|
struct reductions *next;
|
|
short number;
|
|
short nreds;
|
|
short rules[1];
|
|
}
|
|
reductions;
|
|
|
|
|
|
|
|
extern int nstates;
|
|
extern core *first_state;
|
|
extern shifts *first_shift;
|
|
extern reductions *first_reduction;
|