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#ifndef lint |
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static const char RCSid[] = "$Id: savestr.c,v 2.6 2003/02/25 02:47:22 greg Exp $"; |
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#endif |
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/* |
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* savestr.c - routines for efficient string storage. |
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* |
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* Savestr(s) stores a shared read-only string. |
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* Freestr(s) indicates a client is finished with a string. |
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* All strings must be null-terminated. There is |
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* no imposed length limit. |
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* Strings stored with savestr(s) can be equated |
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* reliably using their pointer values. |
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* Calls to savestr(s) and freestr(s) should be |
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* balanced (obviously). The last call to freestr(s) |
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* frees memory associated with the string; it should |
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* never be referenced again. |
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* |
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* External symbols declared in standard.h |
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*/ |
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|
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#include "copyright.h" |
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|
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#include <string.h> |
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#include <stdlib.h> |
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|
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#include "standard.h" |
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|
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#ifndef NHASH |
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#define NHASH 509 /* hash table size (prime!) */ |
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#endif |
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|
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typedef struct s_head { |
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struct s_head *next; /* next in hash list */ |
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int nl; /* links count */ |
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} S_HEAD; /* followed by the string itself */ |
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|
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static S_HEAD *stab[NHASH]; |
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|
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#define hash(s) (shash(s)%NHASH) |
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|
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#define string(sp) ((char *)((sp)+1)) |
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|
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#define salloc(str) (S_HEAD *)malloc(sizeof(S_HEAD)+1+strlen(str)) |
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|
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#define sfree(sp) free((void *)(sp)) |
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|
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|
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char * |
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savestr(str) /* save a string */ |
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char *str; |
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{ |
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register int hval; |
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register S_HEAD *sp; |
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|
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if (str == NULL) |
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return(NULL); |
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hval = hash(str); |
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for (sp = stab[hval]; sp != NULL; sp = sp->next) |
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if (!strcmp(str, string(sp))) { |
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sp->nl++; |
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return(string(sp)); |
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} |
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if ((sp = salloc(str)) == NULL) { |
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eputs("Out of memory in savestr\n"); |
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quit(1); |
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} |
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strcpy(string(sp), str); |
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sp->nl = 1; |
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sp->next = stab[hval]; |
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stab[hval] = sp; |
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return(string(sp)); |
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} |
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|
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|
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void |
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freestr(s) /* free a string */ |
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char *s; |
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{ |
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int hval; |
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register S_HEAD *spl, *sp; |
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|
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if (s == NULL) |
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return; |
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hval = hash(s); |
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for (spl = NULL, sp = stab[hval]; sp != NULL; spl = sp, sp = sp->next) |
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if (s == string(sp)) { |
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if (--sp->nl > 0) |
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return; |
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if (spl != NULL) |
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spl->next = sp->next; |
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else |
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stab[hval] = sp->next; |
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sfree(sp); |
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return; |
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} |
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} |
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|
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|
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int |
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shash(s) |
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register char *s; |
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{ |
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register int h = 0; |
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|
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while (*s) |
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h = (h<<1 & 0x7fff) ^ (*s++ & 0xff); |
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return(h); |
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} |
