| 1 |
/* |
| 2 |
|
| 3 |
#ifndef lint |
| 4 |
static char SCCSid[] = "$SunId$ LBL"; |
| 5 |
#endif |
| 6 |
* savestr.c - routines for efficient string storage. |
| 7 |
* |
| 8 |
* Savestr(s) stores a shared read-only string. |
| 9 |
* Freestr(s) indicates a client is finished with a string. |
| 10 |
* All strings must be null-terminated. There is |
| 11 |
* no imposed length limit. |
| 12 |
* Strings stored with savestr(s) can be equated |
| 13 |
* reliably using their pointer values. A tailored version |
| 14 |
* of strcmp(s1,s2) is included. |
| 15 |
* Calls to savestr(s) and freestr(s) should be |
| 16 |
* balanced (obviously). The last call to freestr(s) |
| 17 |
* frees memory associated with the string; it should |
| 18 |
* never be referenced again. |
| 19 |
* |
| 20 |
* 5/14/87 |
| 21 |
*/ |
| 22 |
|
| 23 |
#ifndef NHASH |
| 24 |
#define NHASH 509 /* hash table size (prime!) */ |
| 25 |
#endif |
| 26 |
|
| 27 |
typedef struct s_head { |
| 28 |
struct s_head *next; /* next in hash list */ |
| 29 |
int nl; /* links count */ |
| 30 |
} S_HEAD; /* followed by the string itself */ |
| 31 |
|
| 32 |
static S_HEAD *stab[NHASH]; |
| 33 |
|
| 34 |
extern char *savestr(), *strcpy(), *malloc(); |
| 35 |
|
| 36 |
#define NULL 0 |
| 37 |
|
| 38 |
#define string(sp) ((char *)((sp)+1)) |
| 39 |
|
| 40 |
#define salloc(str) (S_HEAD *)malloc(sizeof(S_HEAD)+1+strlen(str)) |
| 41 |
|
| 42 |
#define sfree(sp) free((char *)(sp)) |
| 43 |
|
| 44 |
|
| 45 |
char * |
| 46 |
savestr(str) /* save a string */ |
| 47 |
char *str; |
| 48 |
{ |
| 49 |
register int hval; |
| 50 |
register S_HEAD *sp; |
| 51 |
|
| 52 |
if (str == NULL) |
| 53 |
return(NULL); |
| 54 |
hval = shash(str); |
| 55 |
for (sp = stab[hval]; sp != NULL; sp = sp->next) |
| 56 |
if (!strcmp(str, string(sp))) { |
| 57 |
sp->nl++; |
| 58 |
return(string(sp)); |
| 59 |
} |
| 60 |
if ((sp = salloc(str)) == NULL) { |
| 61 |
eputs("Out of memory in savestr\n"); |
| 62 |
quit(1); |
| 63 |
} |
| 64 |
strcpy(string(sp), str); |
| 65 |
sp->nl = 1; |
| 66 |
sp->next = stab[hval]; |
| 67 |
stab[hval] = sp; |
| 68 |
return(string(sp)); |
| 69 |
} |
| 70 |
|
| 71 |
|
| 72 |
freestr(s) /* free a string */ |
| 73 |
char *s; |
| 74 |
{ |
| 75 |
int hval; |
| 76 |
register S_HEAD *spl, *sp; |
| 77 |
|
| 78 |
if (s == NULL) |
| 79 |
return; |
| 80 |
hval = shash(s); |
| 81 |
for (spl = NULL, sp = stab[hval]; sp != NULL; spl = sp, sp = sp->next) |
| 82 |
if (s == string(sp)) { |
| 83 |
if (--sp->nl > 0) |
| 84 |
return; |
| 85 |
if (spl != NULL) |
| 86 |
spl->next = sp->next; |
| 87 |
else |
| 88 |
stab[hval] = sp->next; |
| 89 |
sfree(sp); |
| 90 |
return; |
| 91 |
} |
| 92 |
} |
| 93 |
|
| 94 |
|
| 95 |
int |
| 96 |
strcmp(s1, s2) /* check for s1==s2 */ |
| 97 |
register char *s1, *s2; |
| 98 |
{ |
| 99 |
if (s1 == s2) |
| 100 |
return(0); |
| 101 |
|
| 102 |
while (*s1 == *s2++) |
| 103 |
if (!*s1++) |
| 104 |
return(0); |
| 105 |
|
| 106 |
return(*s1 - *--s2); |
| 107 |
} |
| 108 |
|
| 109 |
|
| 110 |
static int |
| 111 |
shash(s) /* hash a string */ |
| 112 |
register char *s; |
| 113 |
{ |
| 114 |
register int h = 0; |
| 115 |
|
| 116 |
while (*s) |
| 117 |
h += *s++; |
| 118 |
|
| 119 |
return(h % NHASH); |
| 120 |
} |
