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b6b9d458 | 1 | .\" -*-nroff-*- |
2 | .de VS | |
3 | .sp 1 | |
d66d7727 | 4 | .RS |
b6b9d458 | 5 | .nf |
6 | .ft B | |
7 | .. | |
8 | .de VE | |
9 | .ft R | |
10 | .fi | |
11 | .RE | |
12 | .sp 1 | |
13 | .. | |
fbf20b5b | 14 | .TH sym 3 "8 May 1999" "Straylight/Edgeware" "mLib utilities library" |
b6b9d458 | 15 | .SH NAME |
16 | sym \- symbol table manager | |
08da152e | 17 | .\" @sym_create |
18 | .\" @sym_destroy | |
19 | .\" @sym_find | |
20 | .\" @sym_remove | |
21 | .\" @sym_mkiter | |
22 | .\" @sym_next | |
23 | .\" | |
24 | .\" @SYM_NAME | |
0c404077 | 25 | .\" @SYM_LEN |
26 | .\" @SYM_HASH | |
08da152e | 27 | .\" |
b6b9d458 | 28 | .SH SYNOPSIS |
29 | .nf | |
30 | .B "#include <mLib/sym.h>" | |
31 | ||
32 | .BI "void sym_create(sym_table *" t ); | |
33 | .BI "void sym_destroy(sym_table *" t ); | |
34 | ||
2b1924c2 MW |
35 | .ds mT \fBvoid *sym_find( |
36 | .BI "\*(mTsym_table *" t , | |
37 | .BI "\h'\w'\*(mT'u'const char *" n ", long " l , | |
38 | .BI "\h'\w'\*(mT'u'size_t " sz ", unsigned *" f ); | |
b6b9d458 | 39 | .BI "void sym_remove(sym_table *" t ", void *" b ); |
40 | ||
0c404077 | 41 | .BI "const char *SYM_NAME(const void *" p ); |
42 | .BI "size_t SYM_LEN(const void *" p ); | |
43 | .BI "uint32 SYM_HASH(const void *" p ); | |
44 | ||
b6b9d458 | 45 | .BI "void sym_mkiter(sym_iter *" i ", sym_table *" t ); |
46 | .BI "void *sym_next(sym_iter *" i ); | |
47 | .fi | |
0c404077 | 48 | .SH "DESCRIPTION" |
b6b9d458 | 49 | The |
50 | .B sym | |
51 | functions implement a data structure often described as a dictionary, a | |
52 | finite map, an associative array, or a symbol table. It associates | |
53 | .I values | |
54 | with | |
55 | .I keys | |
56 | such that the value corresponding to a given key can be found quickly. | |
57 | Additionally, all stored associations can be enumerated. | |
58 | .PP | |
59 | The interface provides an | |
60 | .I intrusive | |
61 | symbol table. The data objects stored in the table must include a small | |
62 | header used by the symbol table manager. This reduces the amount of | |
63 | pointer fiddling that needs to be done, and in practice doesn't seem to | |
64 | be much of a problem. It's also fairly easy to construct a | |
65 | non-intrusive interface if you really want one. | |
66 | .PP | |
67 | There are three main data structures involved in the interface: | |
68 | .TP | |
69 | .B sym_table | |
70 | Keeps track of the information associated with a particular table. | |
71 | .TP | |
72 | .B sym_base | |
73 | The header which must be attached to the front of all the value | |
74 | objects. | |
75 | .TP | |
76 | .B sym_iter | |
77 | An iterator object, used for enumerating all of the associations stored | |
78 | in a symbol table. | |
79 | .PP | |
80 | All of the above data structures should be considered | |
81 | .IR opaque : | |
82 | don't try looking inside. Representations have changed in the past, and | |
83 | they may change again in the future. | |
0c404077 | 84 | .SS "Creation and destruction" |
b6b9d458 | 85 | The |
86 | .B sym_table | |
87 | object itself needs to be allocated by the caller. It is initialized by | |
88 | passing it to the function | |
89 | .BR sym_create . | |
90 | After initialization, the table contains no entries. | |
91 | .PP | |
92 | Initializing a symbol table involves allocating some memory. If this | |
d2a91066 | 93 | allocation fails, an |
b6b9d458 | 94 | .B EXC_NOMEM |
95 | exception is raised. | |
96 | .PP | |
97 | When a symbol table is no longer needed, the memory occupied by the | |
98 | values and other maintenance structures can be reclaimed by calling | |
99 | .BR sym_destroy . | |
0c404077 | 100 | Any bits of user data attached to values should previously have been |
101 | destroyed. | |
102 | .SS "Adding, searching and removing" | |
b6b9d458 | 103 | Most of the actual work is done by the function |
104 | .BR sym_find . | |
105 | It does both lookup and creation, depending on its arguments. To do its | |
106 | job, it needs to know the following bits of information: | |
107 | .TP | |
ff76c38f | 108 | .BI "sym_table *" t |
b6b9d458 | 109 | A pointer to a symbol table to manipulate. |
110 | .TP | |
ff76c38f | 111 | .BI "const char *" n |
b6b9d458 | 112 | The address of the |
113 | .I key | |
114 | to look up or create. Usually this will be a simple text string, | |
115 | although it can actually be any arbitrary binary data. | |
116 | .TP | |
ff76c38f | 117 | .BI "long " l |
b6b9d458 | 118 | The length of the key. If this is \-1, |
119 | .B sym_find | |
120 | assumes that the key is a null-terminated string, and calculates its | |
0c404077 | 121 | length itself. This is entirely equivalent to passing |
122 | .BI strlen( n )\fR. | |
b6b9d458 | 123 | .TP |
ff76c38f | 124 | .BI "size_t " sz |
b6b9d458 | 125 | The size of the value block to allocate if the key could not be found. |
126 | If this is zero, no value is allocated, and a null pointer is returned | |
127 | to indicate an unsuccessful lookup. | |
128 | .TP | |
ff76c38f | 129 | .BI "unsigned *" f |
b6b9d458 | 130 | The address of a `found' flag to set. This is an output parameter. On |
131 | exit, | |
132 | .B sym_find | |
133 | will set the value of | |
134 | .BI * f | |
135 | to zero if the key could not be found, or nonzero if it was found. This | |
136 | can be used to tell whether the value returned has been newly allocated, | |
137 | or whether it was already in the table. | |
138 | .PP | |
0c404077 | 139 | A terminating null byte is appended to the copy of the symbol's name in |
140 | memory. This is not considered to be a part of the symbol's name, and | |
141 | does not contribute to the name's length as reported by the | |
142 | .B SYM_LEN | |
143 | macro. | |
b6b9d458 | 144 | .PP |
145 | A symbol can be removed from the table by calling | |
146 | .BR sym_remove , | |
147 | passing the symbol table itself, and the value block that needs | |
148 | removing. | |
0c404077 | 149 | .SS "Enquiries about symbols" |
150 | Three macros are provided to enable simple enquiries about a symbol. | |
151 | Given a pointer | |
152 | .I s | |
153 | to a symbol table entry, | |
154 | .BI SYM_LEN( s ) | |
155 | returns the length of the symbol's name (excluding any terminating null | |
d4efbcd9 | 156 | byte); |
0c404077 | 157 | .BI SYM_NAME( s ) |
158 | returns a pointer to the symbol's name; and | |
159 | .BI SYM_HASH( s ) | |
160 | returns the symbol's hash value. | |
161 | .SS "Enumerating symbols" | |
b6b9d458 | 162 | Enumerating the values in a symbol table is fairly simple. Allocate a |
163 | .B sym_iter | |
164 | object from somewhere. Attach it to a symbol table by calling | |
165 | .BR sym_mkiter , | |
166 | and passing in the addresses of the iterator and the symbol table. | |
167 | Then, each call to | |
168 | .B sym_next | |
169 | will return a different value from the symbol table, until all of them | |
170 | have been enumerated, at which point, | |
171 | .B sym_next | |
172 | returns a null pointer. | |
173 | .PP | |
174 | It's safe to remove the symbol you've just been returned by | |
175 | .BR sym_next . | |
176 | However, it's not safe to remove any other symbol. So don't do that. | |
177 | .PP | |
178 | When you've finished with an iterator, it's safe to just throw it away. | |
179 | You don't need to call any functions beforehand. | |
0c404077 | 180 | .SS "Use in practice" |
b6b9d458 | 181 | In normal use, the keys are simple strings (usually identifiers from |
182 | some language), and the values are nontrivial structures providing | |
183 | information about types and values. | |
184 | .PP | |
185 | In this case, you'd define something like the following structure for | |
186 | your values: | |
187 | .VS | |
188 | typedef struct val { | |
189 | sym_base _base; /* Symbol header */ | |
190 | unsigned type; /* Type of this symbol */ | |
191 | int dispoff; /* Which display variable is in */ | |
192 | size_t frameoff; /* Offset of variable in frame */ | |
193 | } val; | |
194 | .VE | |
195 | Given a pointer | |
196 | .I v | |
197 | to a | |
198 | .BR val , | |
199 | you can find the variable's name by calling | |
200 | .BI SYM_NAME( v )\fR. | |
201 | .PP | |
202 | You can look up a name in the table by saying something like: | |
203 | .VS | |
204 | val *v = sym_find(t, name, -1, 0, 0); | |
205 | if (!v) | |
206 | error("unknown variable `%s'", name); | |
207 | .VE | |
208 | You can add in a new variable by saying something like | |
209 | .VS | |
210 | unsigned f; | |
211 | val *v = sym_find(t, name, -1, sizeof(val), &f); | |
212 | if (f) | |
213 | error("variable `%s' already exists", name); | |
214 | /* fill in v */ | |
215 | .VE | |
216 | You can examine all the variables in your symbol table by saying | |
217 | something like: | |
218 | .VS | |
219 | sym_iter i; | |
220 | val *v; | |
221 | ||
222 | for (sym_mkiter(&i, t); (v = sym_next(&i)) != 0; ) { | |
223 | /* ... */ | |
224 | } | |
225 | .VE | |
226 | That ought to be enough examples to be getting on with. | |
0c404077 | 227 | .SS Implementation |
6f444bda | 228 | The symbol table is an extensible hashtable, using the universal hash |
229 | function described in | |
230 | .BR unihash (3) | |
231 | and the global hashing key. The hash chains are kept very short | |
232 | (probably too short, actually). Every time a symbol is found, its block | |
233 | is promoted to the front of its bin chain so it gets found faster next | |
234 | time. | |
b6b9d458 | 235 | .SH SEE ALSO |
0c404077 | 236 | .BR hash (3), |
08da152e | 237 | .BR mLib (3). |
b6b9d458 | 238 | .SH AUTHOR |
9b5ac6ff | 239 | Mark Wooding, <mdw@distorted.org.uk> |