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sdbm.c

/*
 * sdbm - ndbm work-alike hashed database library
 * based on Per-Aake Larson's Dynamic Hashing algorithms. BIT 18 (1978).
 * author: oz@nexus.yorku.ca
 * status: public domain.
 *
 * core routines
 */

#ifndef lint
static char rcsid[] = "$Id: sdbm.c,v 1.2 1998/05/12 03:59:05 riley Exp $";
#endif

#include "sdbm.h"
#include "tune.h"
#include "pair.h"

#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>

#if HAVE_FCNTL_H
#include <fcntl.h>
#else
#include <sys/file.h>
#endif

#if STDC_HEADERS || HAVE_STRING_H
#include <string.h>
/* An ANSI string.h and pre-ANSI memory.h might conflict.  */
#if !STDC_HEADERS && HAVE_MEMORY_H
#include <memory.h>
#endif /* not STDC_HEADERS and HAVE_MEMORY_H */
#define index           strchr
#define rindex          strrchr
#define bcopy(s, d, n)  memcpy ((d), (s), (n))
#define bcmp(s1, s2, n) memcmp ((s1), (s2), (n))
#define bzero(s, n)     memset ((s), 0, (n))
#else /* not STDC_HEADERS and not HAVE_STRING_H */
#include <strings.h>
/* memory.h and strings.h conflict on some systems.  */
#endif /* not STDC_HEADERS and not HAVE_STRING_H */

#ifdef __STDC__
#include <stddef.h>
#endif

#ifndef NULL
#define NULL      0
#endif

/*
 * externals
 */
#ifndef sun
extern int errno;
#endif

extern char *malloc proto((unsigned int));
extern void free proto((void *));
extern long lseek();

/*
 * forward
 */
static int getdbit proto((DBM *, long));
static int setdbit proto((DBM *, long));
static int getpage proto((DBM *, long));
static datum getnext proto((DBM *));
static int makroom proto((DBM *, long, int));

/*
 * useful macros
 */
#define bad(x)          ((x).dptr == NULL || (x).dsize <= 0)
#define exhash(item)    dbm_hash((item).dptr, (item).dsize)
#define ioerr(db) ((db)->flags |= DBM_IOERR)

#define OFF_PAG(off)    (long) (off) * PBLKSIZ
#define OFF_DIR(off)    (long) (off) * DBLKSIZ

static long masks[] = {
      000000000000, 000000000001, 000000000003, 000000000007,
      000000000017, 000000000037, 000000000077, 000000000177,
      000000000377, 000000000777, 000000001777, 000000003777,
      000000007777, 000000017777, 000000037777, 000000077777,
      000000177777, 000000377777, 000000777777, 000001777777,
      000003777777, 000007777777, 000017777777, 000037777777,
      000077777777, 000177777777, 000377777777, 000777777777,
      001777777777, 003777777777, 007777777777, 017777777777
};

datum nullitem = {NULL, 0};

DBM *
dbm_open(file, flags, mode)
register char *file;
register int flags;
register int mode;
{
      register DBM *db;
      register char *dirname;
      register char *pagname;
      register int n;

      if (file == NULL || !*file)
            return errno = EINVAL, (DBM *) NULL;
/*
 * need space for two seperate filenames
 */
      n = strlen(file) * 2 + strlen(DIRFEXT) + strlen(PAGFEXT) + 2;

      if ((dirname = malloc((unsigned) n)) == NULL)
            return errno = ENOMEM, (DBM *) NULL;
/*
 * build the file names
 */
      dirname = strcat(strcpy(dirname, file), DIRFEXT);
      pagname = strcpy(dirname + strlen(dirname) + 1, file);
      pagname = strcat(pagname, PAGFEXT);

      db = dbm_prep(dirname, pagname, flags, mode);
      free((char *) dirname);
      return db;
}

DBM *
dbm_prep(dirname, pagname, flags, mode)
char *dirname;
char *pagname;
int flags;
int mode;
{
      register DBM *db;
      struct stat dstat;

      if ((db = (DBM *) malloc(sizeof(DBM))) == NULL)
            return errno = ENOMEM, (DBM *) NULL;

        db->flags = 0;
        db->hmask = 0;
        db->blkptr = 0;
        db->keyptr = 0;
/*
 * adjust user flags so that WRONLY becomes RDWR, 
 * as required by this package. Also set our internal
 * flag for RDONLY if needed.
 */
      if (flags & O_WRONLY)
            flags = (flags & ~O_WRONLY) | O_RDWR;

      else if ((flags & 03) == O_RDONLY)
            db->flags = DBM_RDONLY;
/*
 * open the files in sequence, and stat the dirfile.
 * If we fail anywhere, undo everything, return NULL.
 */
      if ((db->pagf = open(pagname, flags, mode)) > -1) {
            if ((db->dirf = open(dirname, flags, mode)) > -1) {
/*
 * need the dirfile size to establish max bit number.
 */
                  if (fstat(db->dirf, &dstat) == 0) {
/*
 * zero size: either a fresh database, or one with a single,
 * unsplit data page: dirpage is all zeros.
 */
                        db->dirbno = (!dstat.st_size) ? 0 : -1;
                        db->pagbno = -1;
                        db->maxbno = dstat.st_size * BYTESIZ;

                        (void) memset(db->pagbuf, 0, PBLKSIZ);
                        (void) memset(db->dirbuf, 0, DBLKSIZ);
                  /*
                   * success
                   */
                        return db;
                  }
                  (void) close(db->dirf);
            }
            (void) close(db->pagf);
      }
      free((char *) db);
      return (DBM *) NULL;
}

void
dbm_close(db)
register DBM *db;
{
      if (db == NULL)
            errno = EINVAL;
      else {
            (void) close(db->dirf);
            (void) close(db->pagf);
            free((char *) db);
      }
}

datum
dbm_fetch(db, key)
register DBM *db;
datum key;
{
      if (db == NULL || bad(key))
            return errno = EINVAL, nullitem;

      if (getpage(db, exhash(key)))
            return getpair(db->pagbuf, key);

      return ioerr(db), nullitem;
}

int
dbm_delete(db, key)
register DBM *db;
datum key;
{
      if (db == NULL || bad(key))
            return errno = EINVAL, -1;
      if (dbm_rdonly(db))
            return errno = EPERM, -1;

      if (getpage(db, exhash(key))) {
            if (!delpair(db->pagbuf, key))
                  return -1;
/*
 * update the page file
 */
            if (lseek(db->pagf, OFF_PAG(db->pagbno), SEEK_SET) < 0
                || write(db->pagf, db->pagbuf, PBLKSIZ) < 0)
                  return ioerr(db), -1;

            return 0;
      }

      return ioerr(db), -1;
}

int
dbm_store(db, key, val, flags)
register DBM *db;
datum key;
datum val;
int flags;
{
      int need;
      register long hash;

      if (db == NULL || bad(key))
            return errno = EINVAL, -1;
      if (dbm_rdonly(db))
            return errno = EPERM, -1;

      need = key.dsize + val.dsize;
/*
 * is the pair too big (or too small) for this database ??
 */
      if (need < 0 || need > PAIRMAX)
            return errno = EINVAL, -1;

      if (getpage(db, (hash = exhash(key)))) {
/*
 * if we need to replace, delete the key/data pair
 * first. If it is not there, ignore.
 */
            if (flags == DBM_REPLACE)
                  (void) delpair(db->pagbuf, key);
#ifdef SEEDUPS
            else if (duppair(db->pagbuf, key))
                  return 1;
#endif
/*
 * if we do not have enough room, we have to split.
 */
            if (!fitpair(db->pagbuf, need))
                  if (!makroom(db, hash, need))
                        return ioerr(db), -1;
/*
 * we have enough room or split is successful. insert the key,
 * and update the page file.
 */
            (void) putpair(db->pagbuf, key, val);

            if (lseek(db->pagf, OFF_PAG(db->pagbno), SEEK_SET) < 0
                || write(db->pagf, db->pagbuf, PBLKSIZ) < 0)
                  return ioerr(db), -1;
      /*
       * success
       */
            return 0;
      }

      return ioerr(db), -1;
}

/*
 * makroom - make room by splitting the overfull page
 * this routine will attempt to make room for SPLTMAX times before
 * giving up.
 */
static int
makroom(db, hash, need)
register DBM *db;
long hash;
int need;
{
      long newp;
      char twin[PBLKSIZ];
      char *pag = db->pagbuf;
      char *new = twin;
      register int smax = SPLTMAX;

      do {
/*
 * split the current page
 */
            (void) splpage(pag, new, db->hmask + 1);
/*
 * address of the new page
 */
            newp = (hash & db->hmask) | (db->hmask + 1);

/*
 * write delay, read avoidence/cache shuffle:
 * select the page for incoming pair: if key is to go to the new page,
 * write out the previous one, and copy the new one over, thus making
 * it the current page. If not, simply write the new page, and we are
 * still looking at the page of interest. current page is not updated
 * here, as dbm_store will do so, after it inserts the incoming pair.
 */
            if (hash & (db->hmask + 1)) {
                  if (lseek(db->pagf, OFF_PAG(db->pagbno), SEEK_SET) < 0
                      || write(db->pagf, db->pagbuf, PBLKSIZ) < 0)
                        return 0;
                  db->pagbno = newp;
                  (void) memcpy(pag, new, PBLKSIZ);
            }
            else if (lseek(db->pagf, OFF_PAG(newp), SEEK_SET) < 0
                   || write(db->pagf, new, PBLKSIZ) < 0)
                  return 0;

            if (!setdbit(db, db->curbit))
                  return 0;
/*
 * see if we have enough room now
 */
            if (fitpair(pag, need))
                  return 1;
/*
 * try again... update curbit and hmask as getpage would have
 * done. because of our update of the current page, we do not
 * need to read in anything. BUT we have to write the current
 * [deferred] page out, as the window of failure is too great.
 */
            db->curbit = 2 * db->curbit +
                  ((hash & (db->hmask + 1)) ? 2 : 1);
            db->hmask |= db->hmask + 1;

            if (lseek(db->pagf, OFF_PAG(db->pagbno), SEEK_SET) < 0
                || write(db->pagf, db->pagbuf, PBLKSIZ) < 0)
                  return 0;

      } while (--smax);
/*
 * if we are here, this is real bad news. After SPLTMAX splits,
 * we still cannot fit the key. say goodnight.
 */
#ifdef BADMESS
      (void) write(2, "sdbm: cannot insert after SPLTMAX attempts.\n", 44);
#endif
      return 0;

}

/*
 * the following two routines will break if
 * deletions aren't taken into account. (ndbm bug)
 */
datum
dbm_firstkey(db)
register DBM *db;
{
      if (db == NULL)
            return errno = EINVAL, nullitem;
/*
 * start at page 0
 */
      if (lseek(db->pagf, OFF_PAG(0), SEEK_SET) < 0
          || read(db->pagf, db->pagbuf, PBLKSIZ) < 0)
            return ioerr(db), nullitem;
      db->pagbno = 0;
      db->blkptr = 0;
      db->keyptr = 0;

      return getnext(db);
}

datum
dbm_nextkey(db)
register DBM *db;
{
      if (db == NULL)
            return errno = EINVAL, nullitem;
      return getnext(db);
}

/*
 * all important binary trie traversal
 */
static int
getpage(db, hash)
register DBM *db;
register long hash;
{
      register int hbit;
      register long dbit;
      register long pagb;

      dbit = 0;
      hbit = 0;
      while (dbit < db->maxbno && getdbit(db, dbit))
            dbit = 2 * dbit + ((hash & (1 << hbit++)) ? 2 : 1);

      debug(("dbit: %d...", dbit));

      db->curbit = dbit;
      db->hmask = masks[hbit];

      pagb = hash & db->hmask;
/*
 * see if the block we need is already in memory.
 * note: this lookaside cache has about 10% hit rate.
 */
      if (pagb != db->pagbno) { 
/*
 * note: here, we assume a "hole" is read as 0s.
 * if not, must zero pagbuf first.
 */
            if (lseek(db->pagf, OFF_PAG(pagb), SEEK_SET) < 0
                || read(db->pagf, db->pagbuf, PBLKSIZ) < 0)
                  return 0;
            if (!chkpage(db->pagbuf))
                  return 0;
            db->pagbno = pagb;

            debug(("pag read: %d\n", pagb));
      }
      return 1;
}

static int
getdbit(db, dbit)
register DBM *db;
register long dbit;
{
      register long c;
      register long dirb;

      c = dbit / BYTESIZ;
      dirb = c / DBLKSIZ;

      if (dirb != db->dirbno) {
            if (lseek(db->dirf, OFF_DIR(dirb), SEEK_SET) < 0
                || read(db->dirf, db->dirbuf, DBLKSIZ) < 0)
                  return 0;
            db->dirbno = dirb;

            debug(("dir read: %d\n", dirb));
      }

      return db->dirbuf[c % DBLKSIZ] & (1 << dbit % BYTESIZ);
}

static int
setdbit(db, dbit)
register DBM *db;
register long dbit;
{
      register long c;
      register long dirb;

      c = dbit / BYTESIZ;
      dirb = c / DBLKSIZ;

      if (dirb != db->dirbno) {
            if (lseek(db->dirf, OFF_DIR(dirb), SEEK_SET) < 0
                || read(db->dirf, db->dirbuf, DBLKSIZ) < 0)
                  return 0;
            db->dirbno = dirb;

            debug(("dir read: %d\n", dirb));
      }

      db->dirbuf[c % DBLKSIZ] |= (1 << dbit % BYTESIZ);

      if (dbit >= db->maxbno)
            db->maxbno += DBLKSIZ * BYTESIZ;

      if (lseek(db->dirf, OFF_DIR(dirb), SEEK_SET) < 0
          || write(db->dirf, db->dirbuf, DBLKSIZ) < 0)
            return 0;

      return 1;
}

/*
 * getnext - get the next key in the page, and if done with
 * the page, try the next page in sequence
 */
static datum
getnext(db)
register DBM *db;
{
      datum key;

      for (;;) {
            db->keyptr++;
            key = getnkey(db->pagbuf, db->keyptr);
            if (key.dptr != NULL)
                  return key;
/*
 * we either run out, or there is nothing on this page..
 * try the next one... If we lost our position on the
 * file, we will have to seek.
 */
            db->keyptr = 0;
            if (db->pagbno != db->blkptr++)
                  if (lseek(db->pagf, OFF_PAG(db->blkptr), SEEK_SET) < 0)
                        break;
            db->pagbno = db->blkptr;
            if (read(db->pagf, db->pagbuf, PBLKSIZ) <= 0)
                  break;
            if (!chkpage(db->pagbuf))
                  break;
      }

      return ioerr(db), nullitem;
}

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