1 |
#ifndef lint |
2 |
static const char RCSid[] = "$Id: savestr.c,v 2.9 2003/11/14 17:22:06 schorsch Exp $"; |
3 |
#endif |
4 |
/* |
5 |
* savestr.c - routines for efficient string storage. |
6 |
* |
7 |
* Savestr(s) stores a shared read-only string. |
8 |
* Freestr(s) indicates a client is finished with a string. |
9 |
* All strings must be null-terminated. There is |
10 |
* no imposed length limit. |
11 |
* Strings stored with savestr(s) can be equated |
12 |
* reliably using their pointer values. |
13 |
* Calls to savestr(s) and freestr(s) should be |
14 |
* balanced (obviously). The last call to freestr(s) |
15 |
* frees memory associated with the string; it should |
16 |
* never be referenced again. |
17 |
* |
18 |
* External symbols declared in standard.h |
19 |
*/ |
20 |
|
21 |
#include "copyright.h" |
22 |
|
23 |
#include <string.h> |
24 |
#include <stdlib.h> |
25 |
|
26 |
#include "rtmisc.h" |
27 |
#include "rterror.h" |
28 |
#include "rtio.h" |
29 |
|
30 |
#ifndef NHASH |
31 |
#define NHASH 2039 /* hash table size (prime!) */ |
32 |
#endif |
33 |
|
34 |
typedef struct s_head { |
35 |
struct s_head *next; /* next in hash list */ |
36 |
int nl; /* links count */ |
37 |
} S_HEAD; /* followed by the string itself */ |
38 |
|
39 |
static S_HEAD *stab[NHASH]; |
40 |
|
41 |
#define hash(s) (shash(s)%NHASH) |
42 |
|
43 |
#define string(sp) ((char *)((sp)+1)) |
44 |
|
45 |
#define salloc(str) (S_HEAD *)malloc(sizeof(S_HEAD)+1+strlen(str)) |
46 |
|
47 |
#define sfree(sp) free((void *)(sp)) |
48 |
|
49 |
|
50 |
char * |
51 |
savestr(char *str) /* save a string */ |
52 |
{ |
53 |
register int hval; |
54 |
register S_HEAD *sp; |
55 |
|
56 |
if (str == NULL) |
57 |
return(NULL); |
58 |
hval = hash(str); |
59 |
for (sp = stab[hval]; sp != NULL; sp = sp->next) |
60 |
if (!strcmp(str, string(sp))) { |
61 |
sp->nl++; |
62 |
return(string(sp)); |
63 |
} |
64 |
if ((sp = salloc(str)) == NULL) { |
65 |
eputs("Out of memory in savestr\n"); |
66 |
quit(1); |
67 |
} |
68 |
strcpy(string(sp), str); |
69 |
sp->nl = 1; |
70 |
sp->next = stab[hval]; |
71 |
stab[hval] = sp; |
72 |
return(string(sp)); |
73 |
} |
74 |
|
75 |
|
76 |
void |
77 |
freestr(char *s) /* free a string */ |
78 |
{ |
79 |
int hval; |
80 |
register S_HEAD *spl, *sp; |
81 |
|
82 |
if (s == NULL) |
83 |
return; |
84 |
hval = hash(s); |
85 |
for (spl = NULL, sp = stab[hval]; sp != NULL; spl = sp, sp = sp->next) |
86 |
if (s == string(sp)) { |
87 |
if (--sp->nl > 0) |
88 |
return; |
89 |
if (spl != NULL) |
90 |
spl->next = sp->next; |
91 |
else |
92 |
stab[hval] = sp->next; |
93 |
sfree(sp); |
94 |
return; |
95 |
} |
96 |
} |
97 |
|
98 |
|
99 |
int |
100 |
shash(register char *s) |
101 |
{ |
102 |
register int h = 0; |
103 |
|
104 |
while (*s) |
105 |
h = (h<<1 & 0x7fff) ^ (*s++ & 0xff); |
106 |
return(h); |
107 |
} |