.ref-8c8a5b54e79564c14fc7a2823a21a8f048449bcf/usr/src/lib/libc/db/hash/page.h

/*-
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Margo Seltzer.
 *
 * %sccs.include.redist.c%
 *
 *      @(#)page.h      5.1 (Berkeley) %G%
 */

/*
    Definitions for hashing page file format.
*/
extern  HTAB    *hashp;
/*
 * routines dealing with a data page
 *
 * page format:
 *      +------------------------------+
 * p    | n | keyoff | datoff | keyoff |
 *      +------------+--------+--------+
 *      | datoff | free  |  ptr  | --> |
 *      +--------+---------------------+
 *      |        F R E E A R E A       |
 *      +--------------+---------------+
 *      |  <---- - - - | data          |
 *      +--------+-----+----+----------+
 *      |  key   | data     | key      |
 *      +--------+----------+----------+
 *
 * Pointer to the free space is always:  p[p[0] + 2]
 * Amount of free space on the page is:  p[p[0] + 1]
 */

/*
    How many bytes required for this pair?
    2 shorts in the table at the top of the page +
    room for the key and room for the data

    We prohibit entering a pair on a page unless there is also
    room to append an overflow page. The reason for this it that
    you can get in a situation where a single key/data pair fits
    on a page, but you can't append an overflow page and later
    you'd have to split the key/data and handle like a big pair.
    You might as well do this up front.

*/
#define PAIRSIZE(K,D)   (2*sizeof(u_short) + K->size + D->size)
#define BIGOVERHEAD     (4*sizeof(u_short))
#define KEYSIZE(K)      (4*sizeof(u_short) + K->size);
#define OVFLSIZE        (2*sizeof(u_short))
#define FREESPACE(P)    (P[P[0]+1])
#define OFFSET(P)       (P[P[0]+2])
#define PAIRFITS(P,K,D) ((P[1] >= REAL_KEY) && \
                         (PAIRSIZE(K,D) + OVFLSIZE) <= FREESPACE(P))
#define PAGE_META(N)    ((N+3) * sizeof(u_short))

typedef struct {
    BUFHEAD     *newp;
    BUFHEAD     *oldp;
    BUFHEAD     *nextp;
    u_short     next_addr;
} SPLIT_RETURN;