/*      $NetBSD: hash_page.c,v 1.30 2025/12/16 12:39:02 nia Exp $       */

/*-
 * Copyright (c) 1990, 1993, 1994
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Margo Seltzer.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#if HAVE_NBTOOL_CONFIG_H
#include "nbtool_config.h"
#endif

#include <sys/cdefs.h>
__RCSID("$NetBSD: hash_page.c,v 1.30 2025/12/16 12:39:02 nia Exp $");

/*
 * PACKAGE:  hashing
 *
 * DESCRIPTION:
 *      Page manipulation for hashing package.
 *
 * ROUTINES:
 *
 * External
 *      __get_page
 *      __add_ovflpage
 * Internal
 *      overflow_page
 */

#include "namespace.h"

#include <sys/types.h>
#include <sys/endian.h>

#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <paths.h>
#include <assert.h>

#include <db.h>
#include "hash.h"
#include "page.h"
#include "extern.h"

static uint32_t *fetch_bitmap(HTAB *, int);
static uint32_t  first_free(uint32_t);
static uint16_t  overflow_page(HTAB *);
static void      putpair(char *, const DBT *, const DBT *);
static void      squeeze_key(uint16_t *, const DBT *, const DBT *);
static int       ugly_split(HTAB *, uint32_t, BUFHEAD *, BUFHEAD *, int, int);

#define PAGE_INIT(P) { \
        ((uint16_t *)(void *)(P))[0] = 0; \
        temp = 3 * sizeof(uint16_t); \
        _DIAGASSERT((size_t)HASH_BSIZE(hashp) >= temp); \
        ((uint16_t *)(void *)(P))[1] = (uint16_t)(HASH_BSIZE(hashp) - temp); \
        ((uint16_t *)(void *)(P))[2] = HASH_BSIZE(hashp); \
}

/*
 * This is called AFTER we have verified that there is room on the page for
 * the pair (PAIRFITS has returned true) so we go right ahead and start moving
 * stuff on.
 */
static void
putpair(char *p, const DBT *key, const DBT *val)
{
        uint16_t *bp, n, off;
        size_t temp;

        bp = (uint16_t *)(void *)p;

        /* Enter the key first. */
        n = bp[0];

        temp = OFFSET(bp);
        _DIAGASSERT(temp >= key->size);
        off = (uint16_t)(temp - key->size);
        memmove(p + off, key->data, key->size);
        bp[++n] = off;

        /* Now the data. */
        _DIAGASSERT(off >= val->size);
        off -= (uint16_t)val->size;
        memmove(p + off, val->data, val->size);
        bp[++n] = off;

        /* Adjust page info. */
        bp[0] = n;
        temp = (n + 3) * sizeof(uint16_t);
        _DIAGASSERT(off >= temp);
        bp[n + 1] = (uint16_t)(off - temp);
        bp[n + 2] = off;
}

/*
 * Returns:
 *       0 OK
 *      -1 error
 */
int
__delpair(HTAB *hashp, BUFHEAD *bufp, int ndx)
{
        uint16_t *bp, newoff;
        int n;
        uint16_t pairlen;
        size_t temp;

        bp = (uint16_t *)(void *)bufp->page;
        n = bp[0];

        if (bp[ndx + 1] < REAL_KEY)
                return (__big_delete(hashp, bufp));
        if (ndx != 1)
                newoff = bp[ndx - 1];
        else
                newoff = HASH_BSIZE(hashp);
        pairlen = newoff - bp[ndx + 1];

        if (ndx != (n - 1)) {
                /* Hard Case -- need to shuffle keys */
                int i;
                char *src = bufp->page + (int)OFFSET(bp);
                char *dst = src + (int)pairlen;
                memmove(dst, src, (size_t)(bp[ndx + 1] - OFFSET(bp)));

                /* Now adjust the pointers */
                for (i = ndx + 2; i <= n; i += 2) {
                        if (bp[i + 1] == OVFLPAGE) {
                                bp[i - 2] = bp[i];
                                bp[i - 1] = bp[i + 1];
                        } else {
                                bp[i - 2] = bp[i] + pairlen;
                                bp[i - 1] = bp[i + 1] + pairlen;
                        }
                }
        }
        /* Finally adjust the page data */
        bp[n] = OFFSET(bp) + pairlen;
        temp = bp[n + 1] + pairlen + 2 * sizeof(uint16_t);
        _DIAGASSERT(temp <= 0xffff);
        bp[n - 1] = (uint16_t)temp;
        bp[0] = n - 2;
        hashp->NKEYS--;

        bufp->flags |= BUF_MOD;
        return (0);
}
/*
 * Returns:
 *       0 ==> OK
 *      -1 ==> Error
 */
int
__split_page(HTAB *hashp, uint32_t obucket, uint32_t nbucket)
{
        BUFHEAD *new_bufp, *old_bufp;
        uint16_t *ino;
        char *np;
        DBT key, val;
        int n, ndx, retval;
        uint16_t copyto, diff, off, moved;
        char *op;
        size_t temp;

        copyto = HASH_BSIZE(hashp);
        off = HASH_BSIZE(hashp);
        old_bufp = __get_buf(hashp, obucket, NULL, 0);
        if (old_bufp == NULL)
                return (-1);
        new_bufp = __get_buf(hashp, nbucket, NULL, 0);
        if (new_bufp == NULL)
                return (-1);

        old_bufp->flags |= (BUF_MOD | BUF_PIN);
        new_bufp->flags |= (BUF_MOD | BUF_PIN);

        ino = (uint16_t *)(void *)(op = old_bufp->page);
        np = new_bufp->page;

        moved = 0;

        for (n = 1, ndx = 1; n < ino[0]; n += 2) {
                if (ino[n + 1] < REAL_KEY) {
                        retval = ugly_split(hashp, obucket, old_bufp, new_bufp,
                            (int)copyto, (int)moved);
                        old_bufp->flags &= ~BUF_PIN;
                        new_bufp->flags &= ~BUF_PIN;
                        return (retval);

                }
                key.data = (uint8_t *)op + ino[n];
                key.size = off - ino[n];

                if (__call_hash(hashp, key.data, (int)key.size) == obucket) {
                        /* Don't switch page */
                        diff = copyto - off;
                        if (diff) {
                                copyto = ino[n + 1] + diff;
                                memmove(op + copyto, op + ino[n + 1],
                                    (size_t)(off - ino[n + 1]));
                                ino[ndx] = copyto + ino[n] - ino[n + 1];
                                ino[ndx + 1] = copyto;
                        } else
                                copyto = ino[n + 1];
                        ndx += 2;
                } else {
                        /* Switch page */
                        val.data = (uint8_t *)op + ino[n + 1];
                        val.size = ino[n] - ino[n + 1];
                        putpair(np, &key, &val);
                        moved += 2;
                }

                off = ino[n + 1];
        }

        /* Now clean up the page */
        ino[0] -= moved;
        temp = sizeof(uint16_t) * (ino[0] + 3);
        _DIAGASSERT(copyto >= temp);
        FREESPACE(ino) = (uint16_t)(copyto - temp);
        OFFSET(ino) = copyto;

#ifdef DEBUG3
        (void)fprintf(stderr, "split %d/%d\n",
            ((uint16_t *)np)[0] / 2,
            ((uint16_t *)op)[0] / 2);
#endif
        /* unpin both pages */
        old_bufp->flags &= ~BUF_PIN;
        new_bufp->flags &= ~BUF_PIN;
        return (0);
}

/*
 * Called when we encounter an overflow or big key/data page during split
 * handling.  This is special cased since we have to begin checking whether
 * the key/data pairs fit on their respective pages and because we may need
 * overflow pages for both the old and new pages.
 *
 * The first page might be a page with regular key/data pairs in which case
 * we have a regular overflow condition and just need to go on to the next
 * page or it might be a big key/data pair in which case we need to fix the
 * big key/data pair.
 *
 * Returns:
 *       0 ==> success
 *      -1 ==> failure
 */
static int
ugly_split(
        HTAB *hashp,
        uint32_t obucket,       /* Same as __split_page. */
        BUFHEAD *old_bufp,
        BUFHEAD *new_bufp,
        int copyto,     /* First byte on page which contains key/data values. */
        int moved       /* Number of pairs moved to new page. */
)
{
        BUFHEAD *bufp;  /* Buffer header for ino */
        uint16_t *ino;  /* Page keys come off of */
        uint16_t *np;   /* New page */
        uint16_t *op;   /* Page keys go on to if they aren't moving */
        size_t temp;

        BUFHEAD *last_bfp;      /* Last buf header OVFL needing to be freed */
        DBT key, val;
        SPLIT_RETURN ret;
        uint16_t n, off, ov_addr, scopyto;
        char *cino;             /* Character value of ino */

        bufp = old_bufp;
        ino = (uint16_t *)(void *)old_bufp->page;
        np = (uint16_t *)(void *)new_bufp->page;
        op = (uint16_t *)(void *)old_bufp->page;
        last_bfp = NULL;
        scopyto = (uint16_t)copyto;     /* ANSI */

        n = ino[0] - 1;
        while (n < ino[0]) {
                if (ino[2] < REAL_KEY && ino[2] != OVFLPAGE) {
                        if (__big_split(hashp, old_bufp,
                            new_bufp, bufp, (int)bufp->addr, obucket, &ret))
                                return (-1);
                        old_bufp = ret.oldp;
                        if (!old_bufp)
                                return (-1);
                        op = (uint16_t *)(void *)old_bufp->page;
                        new_bufp = ret.newp;
                        if (!new_bufp)
                                return (-1);
                        np = (uint16_t *)(void *)new_bufp->page;
                        bufp = ret.nextp;
                        if (!bufp)
                                return (0);
                        cino = (char *)bufp->page;
                        ino = (uint16_t *)(void *)cino;
                        last_bfp = ret.nextp;
                } else if (ino[n + 1] == OVFLPAGE) {
                        ov_addr = ino[n];
                        /*
                         * Fix up the old page -- the extra 2 are the fields
                         * which contained the overflow information.
                         */
                        ino[0] -= (moved + 2);
                        temp = sizeof(uint16_t) * (ino[0] + 3);
                        _DIAGASSERT(scopyto >= temp);
                        FREESPACE(ino) = (uint16_t)(scopyto - temp);
                        OFFSET(ino) = scopyto;

                        bufp = __get_buf(hashp, (uint32_t)ov_addr, bufp, 0);
                        if (!bufp)
                                return (-1);

                        ino = (uint16_t *)(void *)bufp->page;
                        n = 1;
                        scopyto = HASH_BSIZE(hashp);
                        moved = 0;

                        if (last_bfp)
                                __free_ovflpage(hashp, last_bfp);
                        last_bfp = bufp;
                }
                /* Move regular sized pairs of there are any */
                off = HASH_BSIZE(hashp);
                for (n = 1; (n < ino[0]) && (ino[n + 1] >= REAL_KEY); n += 2) {
                        cino = (char *)(void *)ino;
                        key.data = (uint8_t *)cino + ino[n];
                        key.size = off - ino[n];
                        val.data = (uint8_t *)cino + ino[n + 1];
                        val.size = ino[n] - ino[n + 1];
                        off = ino[n + 1];

                        if (__call_hash(hashp, key.data, (int)key.size) == obucket) {
                                /* Keep on old page */
                                if (PAIRFITS(op, (&key), (&val)))
                                        putpair((char *)(void *)op, &key, &val);
                                else {
                                        old_bufp =
                                            __add_ovflpage(hashp, old_bufp);
                                        if (!old_bufp)
                                                return (-1);
                                        op = (uint16_t *)(void *)old_bufp->page;
                                        putpair((char *)(void *)op, &key, &val);
                                }
                                old_bufp->flags |= BUF_MOD;
                        } else {
                                /* Move to new page */
                                if (PAIRFITS(np, (&key), (&val)))
                                        putpair((char *)(void *)np, &key, &val);
                                else {
                                        new_bufp =
                                            __add_ovflpage(hashp, new_bufp);
                                        if (!new_bufp)
                                                return (-1);
                                        np = (uint16_t *)(void *)new_bufp->page;
                                        putpair((char *)(void *)np, &key, &val);
                                }
                                new_bufp->flags |= BUF_MOD;
                        }
                }
        }
        if (last_bfp)
                __free_ovflpage(hashp, last_bfp);
        return (0);
}

/*
 * Add the given pair to the page
 *
 * Returns:
 *      0 ==> OK
 *      1 ==> failure
 */
int
__addel(HTAB *hashp, BUFHEAD *bufp, const DBT *key, const DBT *val)
{
        uint16_t *bp, *sop;
        int do_expand;

        bp = (uint16_t *)(void *)bufp->page;
        do_expand = 0;
        while (bp[0] && (bp[2] < REAL_KEY || bp[bp[0]] < REAL_KEY))
                /* Exception case */
                if (bp[2] == FULL_KEY_DATA && bp[0] == 2)
                        /* This is the last page of a big key/data pair
                           and we need to add another page */
                        break;
                else if (bp[2] < REAL_KEY && bp[bp[0]] != OVFLPAGE) {
                        bufp = __get_buf(hashp, (uint32_t)bp[bp[0] - 1], bufp,
                            0);
                        if (!bufp)
                                return (-1);
                        bp = (uint16_t *)(void *)bufp->page;
                } else if (bp[bp[0]] != OVFLPAGE) {
                        /* Short key/data pairs, no more pages */
                        break;
                } else {
                        /* Try to squeeze key on this page */
                        if (bp[2] >= REAL_KEY &&
                            FREESPACE(bp) >= PAIRSIZE(key, val)) {
                                squeeze_key(bp, key, val);
                                goto stats;
                        } else {
                                bufp = __get_buf(hashp,
                                    (uint32_t)bp[bp[0] - 1], bufp, 0);
                                if (!bufp)
                                        return (-1);
                                bp = (uint16_t *)(void *)bufp->page;
                        }
                }

        if (PAIRFITS(bp, key, val))
                putpair(bufp->page, key, val);
        else {
                do_expand = 1;
                bufp = __add_ovflpage(hashp, bufp);
                if (!bufp)
                        return (-1);
                sop = (uint16_t *)(void *)bufp->page;

                if (PAIRFITS(sop, key, val))
                        putpair((char *)(void *)sop, key, val);
                else
                        if (__big_insert(hashp, bufp, key, val))
                                return (-1);
        }
stats:
        bufp->flags |= BUF_MOD;
        /*
         * If the average number of keys per bucket exceeds the fill factor,
         * expand the table.
         */
        hashp->NKEYS++;
        if (do_expand ||
            (hashp->NKEYS / (hashp->MAX_BUCKET + 1) > hashp->FFACTOR))
                return (__expand_table(hashp));
        return (0);
}

/*
 *
 * Returns:
 *      pointer on success
 *      NULL on error
 */
BUFHEAD *
__add_ovflpage(HTAB *hashp, BUFHEAD *bufp)
{
        uint16_t *sp;
        uint16_t ndx, ovfl_num;
        size_t temp;
#ifdef DEBUG1
        int tmp1, tmp2;
#endif
        sp = (uint16_t *)(void *)bufp->page;

        /* Check if we are dynamically determining the fill factor */
        if (hashp->FFACTOR == DEF_FFACTOR) {
                hashp->FFACTOR = (uint32_t)sp[0] >> 1;
                if (hashp->FFACTOR < MIN_FFACTOR)
                        hashp->FFACTOR = MIN_FFACTOR;
        }
        bufp->flags |= BUF_MOD;
        ovfl_num = overflow_page(hashp);
#ifdef DEBUG1
        tmp1 = bufp->addr;
        tmp2 = bufp->ovfl ? bufp->ovfl->addr : 0;
#endif
        if (!ovfl_num || !(bufp->ovfl = __get_buf(hashp, (uint32_t)ovfl_num,
            bufp, 1)))
                return (NULL);
        bufp->ovfl->flags |= BUF_MOD;
#ifdef DEBUG1
        (void)fprintf(stderr, "ADDOVFLPAGE: %d->ovfl was %d is now %d\n",
            tmp1, tmp2, bufp->ovfl->addr);
#endif
        ndx = sp[0];
        /*
         * Since a pair is allocated on a page only if there's room to add
         * an overflow page, we know that the OVFL information will fit on
         * the page.
         */
        sp[ndx + 4] = OFFSET(sp);
        temp = FREESPACE(sp);
        _DIAGASSERT(temp >= OVFLSIZE);
        sp[ndx + 3] = (uint16_t)(temp - OVFLSIZE);
        sp[ndx + 1] = ovfl_num;
        sp[ndx + 2] = OVFLPAGE;
        sp[0] = ndx + 2;
#ifdef HASH_STATISTICS
        hash_overflows++;
#endif
        return (bufp->ovfl);
}

/*
 * Returns:
 *       0 indicates SUCCESS
 *      -1 indicates FAILURE
 */
int
__get_page(HTAB *hashp, char *p, uint32_t bucket, int is_bucket, int is_disk,
    int is_bitmap)
{
        int fd, page, size;
        ssize_t rsize;
        uint16_t *bp;
        size_t temp;

        fd = hashp->fp;
        size = HASH_BSIZE(hashp);

        if ((fd == -1) || !is_disk) {
                PAGE_INIT(p);
                return (0);
        }
        if (is_bucket)
                page = BUCKET_TO_PAGE(bucket);
        else
                page = OADDR_TO_PAGE(bucket);
        if ((rsize = pread(fd, p, (size_t)size, (off_t)page << hashp->BSHIFT)) == -1)
                return (-1);
        bp = (uint16_t *)(void *)p;
        if (!rsize)
                bp[0] = 0;      /* We hit the EOF, so initialize a new page */
        else
                if (rsize != size) {
                        errno = EFTYPE;
                        return (-1);
                }
        if (!is_bitmap && !bp[0]) {
                PAGE_INIT(p);
        } else
                if (hashp->LORDER != BYTE_ORDER) {
                        int i, max;

                        if (is_bitmap) {
                                max = (uint32_t)hashp->BSIZE >> 2; /* divide by 4 */
                                for (i = 0; i < max; i++)
                                        M_32_SWAP(((int *)(void *)p)[i]);
                        } else {
                                M_16_SWAP(bp[0]);
                                max = bp[0] + 2;
                                for (i = 1; i <= max; i++)
                                        M_16_SWAP(bp[i]);
                        }
                }
        return (0);
}

/*
 * Write page p to disk
 *
 * Returns:
 *       0 ==> OK
 *      -1 ==>failure
 */
int
__put_page(HTAB *hashp, char *p, uint32_t bucket, int is_bucket, int is_bitmap)
{
        int fd, page, size;
        ssize_t wsize;
        char pbuf[MAX_BSIZE];

        size = HASH_BSIZE(hashp);
        if ((hashp->fp == -1) && (hashp->fp = __dbtemp("_hash", NULL)) == -1)
                return (-1);
        fd = hashp->fp;

        if (hashp->LORDER != BYTE_ORDER) {
                int i;
                int max;

                memcpy(pbuf, p, size);
                if (is_bitmap) {
                        max = (uint32_t)hashp->BSIZE >> 2;      /* divide by 4 */
                        for (i = 0; i < max; i++)
                                M_32_SWAP(((int *)(void *)pbuf)[i]);
                } else {
                        uint16_t *bp = (uint16_t *)(void *)pbuf;
                        max = bp[0] + 2;
                        for (i = 0; i <= max; i++)
                                M_16_SWAP(bp[i]);
                }
                p = pbuf;
        }
        if (is_bucket)
                page = BUCKET_TO_PAGE(bucket);
        else
                page = OADDR_TO_PAGE(bucket);
        if ((wsize = pwrite(fd, p, (size_t)size, (off_t)page << hashp->BSHIFT)) == -1)
                /* Errno is set */
                return (-1);
        if (wsize != size) {
                errno = EFTYPE;
                return (-1);
        }
        return (0);
}

#define BYTE_MASK       ((1 << INT_BYTE_SHIFT) -1)
/*
 * Initialize a new bitmap page.  Bitmap pages are left in memory
 * once they are read in.
 */
int
__ibitmap(HTAB *hashp, int pnum, int nbits, int ndx)
{
        uint32_t *ip;
        int clearbytes, clearints;

        if ((ip = malloc((size_t)hashp->BSIZE)) == NULL)
                return (1);
        hashp->nmaps++;
        clearints = ((uint32_t)(nbits - 1) >> INT_BYTE_SHIFT) + 1;
        clearbytes = clearints << INT_TO_BYTE;
        (void)memset(ip, 0, (size_t)clearbytes);
        (void)memset(((char *)(void *)ip) + clearbytes, 0xFF,
            (size_t)(hashp->BSIZE - clearbytes));
        ip[clearints - 1] = ALL_SET << (nbits & BYTE_MASK);
        SETBIT(ip, 0);
        hashp->BITMAPS[ndx] = (uint16_t)pnum;
        hashp->mapp[ndx] = ip;
        return (0);
}

static uint32_t
first_free(uint32_t map)
{
        uint32_t i, mask;

        mask = 0x1;
        for (i = 0; i < BITS_PER_MAP; i++) {
                if (!(mask & map))
                        return (i);
                mask = mask << 1;
        }
        return (i);
}

static uint16_t
overflow_page(HTAB *hashp)
{
        uint32_t *freep = NULL;
        int max_free, offset, splitnum;
        uint16_t addr;
        int bit, first_page, free_bit, free_page, i, in_use_bits, j;
#ifdef DEBUG2
        int tmp1, tmp2;
#endif
        splitnum = hashp->OVFL_POINT;
        max_free = hashp->SPARES[splitnum];

        free_page = (uint32_t)(max_free - 1) >> (hashp->BSHIFT + BYTE_SHIFT);
        free_bit = (max_free - 1) & ((hashp->BSIZE << BYTE_SHIFT) - 1);

        /* Look through all the free maps to find the first free block */
        first_page = (uint32_t)hashp->LAST_FREED >>(hashp->BSHIFT + BYTE_SHIFT);
        for ( i = first_page; i <= free_page; i++ ) {
                if (!(freep = (uint32_t *)hashp->mapp[i]) &&
                    !(freep = fetch_bitmap(hashp, i)))
                        return (0);
                if (i == free_page)
                        in_use_bits = free_bit;
                else
                        in_use_bits = (hashp->BSIZE << BYTE_SHIFT) - 1;
                
                if (i == first_page) {
                        bit = hashp->LAST_FREED &
                            ((hashp->BSIZE << BYTE_SHIFT) - 1);
                        j = bit / BITS_PER_MAP;
                        bit = bit & ~(BITS_PER_MAP - 1);
                } else {
                        bit = 0;
                        j = 0;
                }
                for (; bit <= in_use_bits; j++, bit += BITS_PER_MAP)
                        if (freep[j] != ALL_SET)
                                goto found;
        }

        /* No Free Page Found */
        hashp->LAST_FREED = hashp->SPARES[splitnum];
        hashp->SPARES[splitnum]++;
        offset = hashp->SPARES[splitnum] -
            (splitnum ? hashp->SPARES[splitnum - 1] : 0);

#define OVMSG   "HASH: Out of overflow pages.  Increase page size\n"
        if (offset > SPLITMASK) {
                if (++splitnum >= NCACHED) {
                        (void)write(STDERR_FILENO, OVMSG, sizeof(OVMSG) - 1);
                        errno = EFBIG;
                        return (0);
                }
                hashp->OVFL_POINT = splitnum;
                hashp->SPARES[splitnum] = hashp->SPARES[splitnum-1];
                hashp->SPARES[splitnum-1]--;
                offset = 1;
        }

        /* Check if we need to allocate a new bitmap page */
        if (free_bit == (hashp->BSIZE << BYTE_SHIFT) - 1) {
                free_page++;
                if (free_page >= NCACHED) {
                        (void)write(STDERR_FILENO, OVMSG, sizeof(OVMSG) - 1);
                        errno = EFBIG;
                        return (0);
                }
                /*
                 * This is tricky.  The 1 indicates that you want the new page
                 * allocated with 1 clear bit.  Actually, you are going to
                 * allocate 2 pages from this map.  The first is going to be
                 * the map page, the second is the overflow page we were
                 * looking for.  The init_bitmap routine automatically, sets
                 * the first bit of itself to indicate that the bitmap itself
                 * is in use.  We would explicitly set the second bit, but
                 * don't have to if we tell init_bitmap not to leave it clear
                 * in the first place.
                 */
                if (__ibitmap(hashp,
                    (int)OADDR_OF(splitnum, offset), 1, free_page))
                        return (0);
                hashp->SPARES[splitnum]++;
#ifdef DEBUG2
                free_bit = 2;
#endif
                offset++;
                if (offset > SPLITMASK) {
                        if (++splitnum >= NCACHED) {
                                (void)write(STDERR_FILENO, OVMSG,
                                    sizeof(OVMSG) - 1);
                                errno = EFBIG;
                                return (0);
                        }
                        hashp->OVFL_POINT = splitnum;
                        hashp->SPARES[splitnum] = hashp->SPARES[splitnum-1];
                        hashp->SPARES[splitnum-1]--;
                        offset = 0;
                }
        } else {
                /*
                 * Free_bit addresses the last used bit.  Bump it to address
                 * the first available bit.
                 */
                free_bit++;
                SETBIT(freep, free_bit);
        }

        /* Calculate address of the new overflow page */
        addr = OADDR_OF(splitnum, offset);
#ifdef DEBUG2
        (void)fprintf(stderr, "OVERFLOW_PAGE: ADDR: %d BIT: %d PAGE %d\n",
            addr, free_bit, free_page);
#endif
        return (addr);

found:
        bit = bit + first_free(freep[j]);
        SETBIT(freep, bit);
#ifdef DEBUG2
        tmp1 = bit;
        tmp2 = i;
#endif
        /*
         * Bits are addressed starting with 0, but overflow pages are addressed
         * beginning at 1. Bit is a bit addressnumber, so we need to increment
         * it to convert it to a page number.
         */
        bit = 1 + bit + (i * (hashp->BSIZE << BYTE_SHIFT));
        if (bit >= hashp->LAST_FREED)
                hashp->LAST_FREED = bit - 1;

        /* Calculate the split number for this page */
        for (i = 0; (i < splitnum) && (bit > hashp->SPARES[i]); i++);
        offset = (i ? bit - hashp->SPARES[i - 1] : bit);
        if (offset >= SPLITMASK) {
                (void)write(STDERR_FILENO, OVMSG, sizeof(OVMSG) - 1);
                errno = EFBIG;
                return (0);     /* Out of overflow pages */
        }
        addr = OADDR_OF(i, offset);
#ifdef DEBUG2
        (void)fprintf(stderr, "OVERFLOW_PAGE: ADDR: %d BIT: %d PAGE %d\n",
            addr, tmp1, tmp2);
#endif

        /* Allocate and return the overflow page */
        return (addr);
}

/*
 * Mark this overflow page as free.
 */
void
__free_ovflpage(HTAB *hashp, BUFHEAD *obufp)
{
        uint16_t addr;
        uint32_t *freep;
        int bit_address, free_page, free_bit;
        uint16_t ndx;

        addr = obufp->addr;
#ifdef DEBUG1
        (void)fprintf(stderr, "Freeing %d\n", addr);
#endif
        ndx = (((uint32_t)addr) >> SPLITSHIFT);
        bit_address =
            (ndx ? hashp->SPARES[ndx - 1] : 0) + (addr & SPLITMASK) - 1;
         if (bit_address < hashp->LAST_FREED)
                hashp->LAST_FREED = bit_address;
        free_page = ((uint32_t)bit_address >> (hashp->BSHIFT + BYTE_SHIFT));
        free_bit = bit_address & ((hashp->BSIZE << BYTE_SHIFT) - 1);

        if (!(freep = hashp->mapp[free_page]))
                freep = fetch_bitmap(hashp, free_page);
        /*
         * This had better never happen.  It means we tried to read a bitmap
         * that has already had overflow pages allocated off it, and we
         * failed to read it from the file.
         */
        _DIAGASSERT(freep != NULL);
        CLRBIT(freep, free_bit);
#ifdef DEBUG2
        (void)fprintf(stderr, "FREE_OVFLPAGE: ADDR: %d BIT: %d PAGE %d\n",
            obufp->addr, free_bit, free_page);
#endif
        __reclaim_buf(hashp, obufp);
}

/*
 * We have to know that the key will fit, but the last entry on the page is
 * an overflow pair, so we need to shift things.
 */
static void
squeeze_key(uint16_t *sp, const DBT *key, const DBT *val)
{
        char *p;
        uint16_t free_space, n, off, pageno;
        size_t temp;

        p = (char *)(void *)sp;
        n = sp[0];
        free_space = FREESPACE(sp);
        off = OFFSET(sp);

        pageno = sp[n - 1];
        _DIAGASSERT(off >= key->size);
        off -= (uint16_t)key->size;
        sp[n - 1] = off;
        memmove(p + off, key->data, key->size);
        _DIAGASSERT(off >= val->size);
        off -= (uint16_t)val->size;
        sp[n] = off;
        memmove(p + off, val->data, val->size);
        sp[0] = n + 2;
        sp[n + 1] = pageno;
        sp[n + 2] = OVFLPAGE;
        temp = PAIRSIZE(key, val);
        _DIAGASSERT(free_space >= temp);
        FREESPACE(sp) = (uint16_t)(free_space - temp);
        OFFSET(sp) = off;
}

static uint32_t *
fetch_bitmap(HTAB *hashp, int ndx)
{
        if (ndx >= hashp->nmaps)
                return (NULL);
        if ((hashp->mapp[ndx] = malloc((size_t)hashp->BSIZE)) == NULL)
                return (NULL);
        if (__get_page(hashp,
            (char *)(void *)hashp->mapp[ndx], (uint32_t)hashp->BITMAPS[ndx], 0, 1, 1)) {
                free(hashp->mapp[ndx]);
                return (NULL);
        }
        return (hashp->mapp[ndx]);
}

#ifdef DEBUG4
void print_chain(HTAB *, uint32_t);
void
print_chain(HTAB *hashp, uint32_t addr)
{
        BUFHEAD *bufp;
        uint16_t *bp, oaddr;

        (void)fprintf(stderr, "%d ", addr);
        bufp = __get_buf(hashp, addr, NULL, 0);
        bp = (uint16_t *)bufp->page;
        while (bp[0] && ((bp[bp[0]] == OVFLPAGE) ||
                ((bp[0] > 2) && bp[2] < REAL_KEY))) {
                oaddr = bp[bp[0] - 1];
                (void)fprintf(stderr, "%d ", (int)oaddr);
                bufp = __get_buf(hashp, (uint32_t)oaddr, bufp, 0);
                bp = (uint16_t *)bufp->page;
        }
        (void)fprintf(stderr, "\n");
}
#endif