/*
 * 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.
 *
 * page-level routines
 */
#include "sdbm.h"
#include "sdbm_tune.h"
#include "sdbm_pair.h"
#include <string.h>       /* for memset() */
#define exhash(item)    sdbm_hash((item).dptr, (item).dsize)
/* 
 * forward 
 */
static int seepair proto((char *, int, char *, int));
/*
 * page format:
 *      +------------------------------+
 * ino  | n | keyoff | datoff | keyoff |
 *      +------------+--------+--------+
 *      | datoff | - - - ---->              |
 *      +--------+---------------------+
 *      |        F R E E A R E A       |
 *      +--------------+---------------+
 *      |  <---- - - - | data          |
 *      +--------+-----+----+----------+
 *      |  key   | data     | key      |
 *      +--------+----------+----------+
 *
 * calculating the offsets for free area:  if the number
 * of entries (ino[0]) is zero, the offset to the END of
 * the free area is the block size. Otherwise, it is the
 * nth (ino[ino[0]]) entry's offset.
 */
int
fitpair(pag, need)
char *pag;
int need;
{
        register int n;
        register int off;
        register int avail;
        register short *ino = (short *) pag;
        off = ((n = ino[0]) > 0) ? ino[n] : PBLKSIZ;
        avail = off - (n + 1) * sizeof(short);
        need += 2 * sizeof(short);
        debug(("avail %d need %d\n", avail, need));
        return need <= avail;
}
void
putpair(pag, key, val)
char *pag;
datum key;
datum val;
{
        register int n;
        register int off;
        register short *ino = (short *) pag;
        off = ((n = ino[0]) > 0) ? ino[n] : PBLKSIZ;
/*
 * enter the key first
 */
        off -= key.dsize;
        (void) memcpy(pag + off, key.dptr, key.dsize);
        ino[n + 1] = off;
/*
 * now the data
 */
        off -= val.dsize;
        (void) memcpy(pag + off, val.dptr, val.dsize);
        ino[n + 2] = off;
/*
 * adjust item count
 */
        ino[0] += 2;
}
datum
getpair(pag, key)
char *pag;
datum key;
{
        register int i;
        register int n;
        datum val;
        register short *ino = (short *) pag;
        if ((n = ino[0]) == 0)
                return nullitem;
        if ((i = seepair(pag, n, key.dptr, key.dsize)) == 0)
                return nullitem;
        val.dptr = pag + ino[i + 1];
        val.dsize = ino[i] - ino[i + 1];
        return val;
}
#ifdef SEEDUPS
int
duppair(pag, key)
char *pag;
datum key;
{
        register short *ino = (short *) pag;
        return ino[0] > 0 && seepair(pag, ino[0], key.dptr, key.dsize) > 0;
}
#endif
datum
getnkey(pag, num)
char *pag;
int num;
{
        datum key;
        register int off;
        register short *ino = (short *) pag;
        num = num * 2 - 1;
        if (ino[0] == 0 || num > ino[0])
                return nullitem;
        off = (num > 1) ? ino[num - 1] : PBLKSIZ;
        key.dptr = pag + ino[num];
        key.dsize = off - ino[num];
        return key;
}
int
delpair(pag, key)
char *pag;
datum key;
{
        register int n;
        register int i;
        register short *ino = (short *) pag;
        if ((n = ino[0]) == 0)
                return 0;
        if ((i = seepair(pag, n, key.dptr, key.dsize)) == 0)
                return 0;
/*
 * found the key. if it is the last entry
 * [i.e. i == n - 1] we just adjust the entry count.
 * hard case: move all data down onto the deleted pair,
 * shift offsets onto deleted offsets, and adjust them.
 * [note: 0 < i < n]
 */
        if (i < n - 1) {
                register int m;
                register char *dst = pag + (i == 1 ? PBLKSIZ : ino[i - 1]);
                register char *src = pag + ino[i + 1];
                register int   zoo = dst - src;
                debug(("free-up %d ", zoo));
/*
 * shift data/keys down
 */
                m = ino[i + 1] - ino[n];
#undef DUFF     /* just use memmove. it should be plenty fast. */
#ifdef DUFF
#define MOVB    *--dst = *--src
                if (m > 0) {
                        register int loop = (m + 8 - 1) >> 3;
                        switch (m & (8 - 1)) {
                        case 0: do {
                                MOVB;   case 7: MOVB;
                        case 6: MOVB;   case 5: MOVB;
                        case 4: MOVB;   case 3: MOVB;
                        case 2: MOVB;   case 1: MOVB;
                                } while (--loop);
                        }
                }
#else
                dst -= m;
                src -= m;
                memmove(dst, src, m);
#endif
/*
 * adjust offset index up
 */
                while (i < n - 1) {
                        ino[i] = ino[i + 2] + zoo;
                        i++;
                }
        }
        ino[0] -= 2;
        return 1;
}
/*
 * search for the key in the page.
 * return offset index in the range 0 < i < n.
 * return 0 if not found.
 */
static int
seepair(pag, n, key, siz)
char *pag;
register int n;
register char *key;
register int siz;
{
        register int i;
        register int off = PBLKSIZ;
        register short *ino = (short *) pag;
        for (i = 1; i < n; i += 2) {
                if (siz == off - ino[i] &&
                    memcmp(key, pag + ino[i], siz) == 0)
                        return i;
                off = ino[i + 1];
        }
        return 0;
}
void
splpage(pag, new, sbit)
char *pag;
char *new;
long sbit;
{
        datum key;
        datum val;
        register int n;
        register int off = PBLKSIZ;
        char cur[PBLKSIZ];
        register short *ino = (short *) cur;
        (void) memcpy(cur, pag, PBLKSIZ);
        (void) memset(pag, 0, PBLKSIZ);
        (void) memset(new, 0, PBLKSIZ);
        n = ino[0];
        for (ino++; n > 0; ino += 2) {
                key.dptr = cur + ino[0]; 
                key.dsize = off - ino[0];
                val.dptr = cur + ino[1];
                val.dsize = ino[0] - ino[1];
/*
 * select the page pointer (by looking at sbit) and insert
 */
                (void) putpair((exhash(key) & sbit) ? new : pag, key, val);
                off = ino[1];
                n -= 2;
        }
        debug(("%d split %d/%d\n", ((short *) cur)[0] / 2, 
               ((short *) new)[0] / 2,
               ((short *) pag)[0] / 2));
}
/*
 * check page sanity: 
 * number of entries should be something
 * reasonable, and all offsets in the index should be in order.
 * this could be made more rigorous.
 */
int
chkpage(pag)
char *pag;
{
        register int n;
        register int off;
        register short *ino = (short *) pag;
        if ((n = ino[0]) < 0 || n > PBLKSIZ / sizeof(short))
                return 0;
        if (n > 0) {
                off = PBLKSIZ;
                for (ino++; n > 0; ino += 2) {
                        if (ino[0] > off || ino[1] > off ||
                            ino[1] > ino[0])
                                return 0;
                        off = ino[1];
                        n -= 2;
                }
        }
        return 1;
}