sdbm_pair.c

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/* Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
/*
 * sdbm - ndbm work-alike hashed database library
 * based on Per-Aake Larson's Dynamic Hashing algorithms. BIT 18 (1978).
 * author: [email protected]
 * status: ex-public domain.
 *
 * page-level routines
 */
 
#include "apr_sdbm.h"
 
#include "sdbm_tune.h"
#include "sdbm_pair.h"
#include "sdbm_private.h"
 
#include <string.h> /* for memset() */
 
 
#define exhash(item)    sdbm_hash((item).dptr, (item).dsize)
 
/* 
 * forward 
 */
static int seepair(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;
apr_sdbm_datum_t key;
apr_sdbm_datum_t 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;
}
 
apr_sdbm_datum_t
getpair(pag, key)
char *pag;
apr_sdbm_datum_t key;
{
    register int i;
    register int n;
    apr_sdbm_datum_t val;
    register short *ino = (short *) pag;
 
    if ((n = ino[0]) == 0)
        return sdbm_nullitem;
 
    if ((i = seepair(pag, n, key.dptr, key.dsize)) == 0)
        return sdbm_nullitem;
 
    val.dptr = pag + ino[i + 1];
    val.dsize = ino[i] - ino[i + 1];
    return val;
}
 
int
duppair(pag, key)
char *pag;
apr_sdbm_datum_t key;
{
    register short *ino = (short *) pag;
    return ino[0] > 0 && seepair(pag, ino[0], key.dptr, key.dsize) > 0;
}
 
apr_sdbm_datum_t
getnkey(pag, num)
char *pag;
int num;
{
    apr_sdbm_datum_t key;
    register int off;
    register short *ino = (short *) pag;
 
    num = num * 2 - 1;
    if (ino[0] == 0 || num > ino[0])
        return sdbm_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;
apr_sdbm_datum_t 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 short zoo = (short) (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;
{
    apr_sdbm_datum_t key;
    apr_sdbm_datum_t 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] < 0 || ino[0] > off ||
                ino[1] < 0 || ino[1] > off ||
                ino[1] > ino[0])
                return 0;
            off = ino[1];
            n -= 2;
        }
    }
    return 1;
}