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1/*  This file is part of the program psim.
2
3    Copyright (C) 1994,1995,1996, Andrew Cagney <cagney@highland.com.au>
4
5    This program is free software; you can redistribute it and/or modify
6    it under the terms of the GNU General Public License as published by
7    the Free Software Foundation; either version 2 of the License, or
8    (at your option) any later version.
9
10    This program is distributed in the hope that it will be useful,
11    but WITHOUT ANY WARRANTY; without even the implied warranty of
12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13    GNU General Public License for more details.
14
15    You should have received a copy of the GNU General Public License
16    along with this program; if not, write to the Free Software
17    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
18
19    */
20
21/* Instruction decode table:
22
23   <options>:<first>:<last>:<force-first>:<force-last>:<force-expand>:<special>...
24
25
26
27   Ignore the below:
28
29
30   The instruction decode table contains rules that dictate how igen
31   is going to firstly break down the opcode table and secondly
32
33   The table that follows is used by gen to construct a decision tree
34   that can identify each possible instruction.  Gen then outputs this
35   decision tree as (according to config) a table or switch statement
36   as the function idecode.
37
38   In parallel to this, as mentioned above, WITH_EXPANDED_SEMANTICS
39   determines of the semantic functions themselves should be expanded
40   in a similar way.
41
42   <first>
43   <last>
44
45   Range of bits (within the instruction) that should be searched for
46   an instruction field.  Within such ranges, gen looks for opcodes
47   (constants), registers (strings) and reserved bits (slash) and
48   according to the rules that follows includes or excludes them from
49   a possible instruction field.
50
51   <force_first>
52   <force_last>
53
54   If an instruction field was found, enlarge the field size so that
55   it is forced to at least include bits starting from <force_first>
56   (<force_last>).  To stop this occuring, use <force_first> = <last>
57   + 1 and <force_last> = <first> - 1.
58
59   <force_slash>
60
61   Treat `/' fields as a constant instead of variable when looking for
62   an instruction field.
63
64   <force_expansion>
65
66   Treat any contained register (string) fields as constant when
67   determining the instruction field.  For the instruction decode (and
68   controled by IDECODE_EXPAND_SEMANTICS) this forces the expansion of
69   what would otherwize be non constant bits of an instruction.
70
71   <use_switch>
72
73   Should this table be expanded using a switch statement (val 1) and
74   if so, should it be padded with entries so as to force the compiler
75   to generate a jump table (val 2). Or a branch table (val 3).
76
77   <special_mask>
78   <special_value>
79   <special_rule>
80   <special_constant>
81
82   Special rule to fine tune how specific (or groups) of instructions
83   are expanded.  The applicability of the rule is determined by
84
85     <special_mask> != 0 && (instruction> & <special_mask>) == <special_value>
86
87   Where <instruction> is obtained by looking only at constant fields
88   with in an instructions spec.  When determining an expansion, the
89   rule is only considered when a node contains a single instruction.
90   <special_rule> can be any of:
91
92        0: for this instruction, expand by earlier rules
93   	1: expand bits <force_low> .. <force_hi> only
94	2: boolean expansion of only zero/non-zero cases
95	3: boolean expansion of equality of special constant
96
97	*/
98
99
100typedef enum {
101  normal_decode_rule,
102  expand_forced_rule,
103  boolean_rule,
104  nr_decode_rules
105} decode_special_type;
106
107typedef enum {
108  invalid_gen,
109  array_gen,
110  switch_gen,
111  padded_switch_gen,
112  goto_switch_gen,
113  nr_decode_gen_types,
114} decode_gen_type;
115
116
117typedef struct _decode_table decode_table;
118struct _decode_table {
119  decode_special_type type;
120  decode_gen_type gen;
121  int first;
122  int last;
123  int force_first;
124  int force_last;
125  int force_slash;
126  char *force_expansion;
127  unsigned special_mask;
128  unsigned special_value;
129  unsigned special_constant;
130  decode_table *next;
131};
132
133
134extern void force_decode_gen_type
135(const char *type);
136
137extern decode_table *load_decode_table
138(char *file_name,
139 int hi_bit_nr);
140
141extern void dump_decode_rule
142(decode_table *rule,
143 int indent);
144