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#ifndef lint
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static const char RCSid[] = "$Id$";
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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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#include "copyright.h"
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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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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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static S_HEAD *stab[NHASH];
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#define hash(s) (shash(s)%NHASH)
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extern char *savestr(), *strcpy(), *malloc();
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#define NULL 0
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#define string(sp) ((char *)((sp)+1))
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#define salloc(str) (S_HEAD *)malloc(sizeof(S_HEAD)+1+strlen(str))
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#define sfree(sp) free((void *)(sp))
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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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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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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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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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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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while (*s)
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h = (h<<1 & 0x7fff) ^ (*s++ & 0xff);
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return(h);
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}
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