/*
* 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 "config.h"
#ifdef __CYGWIN__
# define EXTCONST extern const
#else
# include "EXTERN.h"
#endif
#include "sdbm.h"
#include "tune.h"
#include "pair.h"
#define exhash(item) sdbm_hash((item).dptr, (item).dsize)
/*
* forward
*/
static int seepair(char *, int, const 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(char *pag, int need)
{
int n;
int off;
int free;
short *ino = (short *) pag;
off = ((n = ino[0]) > 0) ? ino[n] : PBLKSIZ;
free = off - (n + 1) * sizeof(short);
need += 2 * sizeof(short);
debug(("free %d need %d\n", free, need));
return need <= free;
}
void
putpair(char *pag, datum key, datum val)
{
int n;
int off;
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(char *pag, datum key)
{
int i;
int n;
datum val;
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;
}
int
exipair(char *pag, datum key)
{
short *ino = (short *) pag;
if (ino[0] == 0)
return 0;
return (seepair(pag, ino[0], key.dptr, key.dsize) != 0);
}
#ifdef SEEDUPS
int
duppair(char *pag, datum key)
{
short *ino = (short *) pag;
return ino[0] > 0 && seepair(pag, ino[0], key.dptr, key.dsize) > 0;
}
#endif
datum
getnkey(char *pag, int num)
{
datum key;
int off;
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(char *pag, datum key)
{
int n;
int i;
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) {
int m;
char *dst = pag + (i == 1 ? PBLKSIZ : ino[i - 1]);
char *src = pag + ino[i + 1];
int zoo = dst - src;
debug(("free-up %d ", zoo));
/*
* shift data/keys down
*/
m = ino[i + 1] - ino[n];
#ifdef DUFF
#define MOVB *--dst = *--src
if (m > 0) {
int loop = (m + 8 - 1) >> 3;
switch (m & (8 - 1)) {
case 0: do {
MOVB; /* FALLTHROUGH */ case 7: MOVB; /* FALLTHROUGH */
case 6: MOVB; /* FALLTHROUGH */ case 5: MOVB; /* FALLTHROUGH */
case 4: MOVB; /* FALLTHROUGH */ case 3: MOVB; /* FALLTHROUGH */
case 2: MOVB; /* FALLTHROUGH */ 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(char *pag, int n, const char *key, int siz)
{
int i;
int off = PBLKSIZ;
short *ino = (short *) pag;
for (i = 1; i < n; i += 2) {
if (siz == off - ino[i] &&
memEQ(key, pag + ino[i], siz))
return i;
off = ino[i + 1];
}
return 0;
}
void
splpage(char *pag, char *New, long int sbit)
{
datum key;
datum val;
int n;
int off = PBLKSIZ;
char cur[PBLKSIZ];
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.
*/
/*
Layout of a page is:
Top of block:
number of keys/values (short)
Array of (number of keys/values) offsets, alternating between key offsets
and value offsets (shorts)
End of block:
- value/key data, last key ends at end of block (bytes)
So:
N key0off val0off key1off val1off ... val1 key1 val0 key0
Be careful to note N is the number of offsets, *not* the number of keys.
*/
int
chkpage(char *pag)
{
int n;
int off;
short *ino = (short *) pag;
if ((n = ino[0]) < 0 || n > (int)(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] || ino[1] <= 0)
return 0;
off = ino[1];
n -= 2;
}
/* there must be an even number of offsets */
if (n != 0)
return 0;
/* check the key/value offsets don't overlap the key/value data */
if ((char *)ino > pag + off)
return 0;
}
return 1;
}