cdb_find.c
上传用户:tany51
上传日期:2013-06-12
资源大小:1397k
文件大小:2k
- /* cdb_find routine
- *
- * This file is a part of tinycdb package by Michael Tokarev, mjt@corpit.ru.
- * Public domain.
- */
- #include "common/setup_before.h"
- #include "cdb_int.h"
- #include "common/setup_after.h"
- int
- cdb_find(struct cdb *cdbp, const void *key, unsigned klen)
- {
- const unsigned char *htp; /* hash table pointer */
- const unsigned char *htab; /* hash table */
- const unsigned char *htend; /* end of hash table */
- unsigned httodo; /* ht bytes left to look */
- unsigned pos, n;
- unsigned hval;
- if (klen >= cdbp->cdb_dend) /* if key size is too large */
- return 0;
- hval = cdb_hash(key, klen);
- /* find (pos,n) hash table to use */
- /* first 2048 bytes (toc) are always available */
- /* (hval % 256) * 8 */
- htp = cdbp->cdb_mem + ((hval << 3) & 2047); /* index in toc (256x8) */
- n = cdb_unpack(htp + 4); /* table size */
- if (!n) /* empty table */
- return 0; /* not found */
- httodo = n << 3; /* bytes of htab to lookup */
- pos = cdb_unpack(htp); /* htab position */
- if (n > (cdbp->cdb_fsize >> 3) /* overflow of httodo ? */
- || pos < cdbp->cdb_dend /* is htab inside data section ? */
- || pos > cdbp->cdb_fsize /* htab start within file ? */
- || httodo > cdbp->cdb_fsize - pos) /* entrie htab within file ? */
- return errno = EPROTO, -1;
- htab = cdbp->cdb_mem + pos; /* htab pointer */
- htend = htab + httodo; /* after end of htab */
- /* htab starting position: rest of hval modulo htsize, 8bytes per elt */
- htp = htab + (((hval >> 8) % n) << 3);
- for(;;) {
- pos = cdb_unpack(htp + 4); /* record position */
- if (!pos)
- return 0;
- if (cdb_unpack(htp) == hval) {
- if (pos > cdbp->cdb_dend - 8) /* key+val lengths */
- return errno = EPROTO, -1;
- if (cdb_unpack(cdbp->cdb_mem + pos) == klen) {
- if (cdbp->cdb_dend - klen < pos + 8)
- return errno = EPROTO, -1;
- if (memcmp(key, cdbp->cdb_mem + pos + 8, klen) == 0) {
- n = cdb_unpack(cdbp->cdb_mem + pos + 4);
- pos += 8;
- if (cdbp->cdb_dend < n || cdbp->cdb_dend - n < pos + klen)
- return errno = EPROTO, -1;
- cdbp->cdb_kpos = pos;
- cdbp->cdb_klen = klen;
- cdbp->cdb_vpos = pos + klen;
- cdbp->cdb_vlen = n;
- return 1;
- }
- }
- }
- httodo -= 8;
- if (!httodo)
- return 0;
- if ((htp += 8) >= htend)
- htp = htab;
- }
- }