windows-server-2003/base/mspatch/lzx/encoder/bsearch.c

/*
 * bsearch.c
 *
 * Binary search for optimal encoder
 */
#include "encoder.h"


#define left    context->enc_Left
#define right   context->enc_Right


/*
 * Define this to force checking that all search locations visited
 * are valid.
 *
 * For debugging purposes only.
 */
#ifdef _DEBUG
    #define VERIFY_SEARCHES
#endif

#define VERIFY_SEARCH_CODE(routine_name) \
{ \
        int debug_search; \
        for (debug_search = 0; debug_search < clen; debug_search++) \
        { \
            _ASSERTE( context->enc_MemWindow[ptr+debug_search] == context->enc_MemWindow[BufPos+debug_search]); \
        } \
}

#define VERIFY_MULTI_TREE_SEARCH_CODE(routine_name) \
_ASSERTE (context->enc_MemWindow[BufPos] == context->enc_MemWindow[ptr]); \
_ASSERTE (context->enc_MemWindow[BufPos+1] == context->enc_MemWindow[ptr+1]);



/*
 * Finds the closest matches of all possible lengths, MIN_MATCH <= x <= MAX_MATCH,
 * at position BufPos.
 *
 * The positions of each match location are stored in context->enc_matchpos_table[]
 *
 * Returns the longest such match length found, or zero if no matches found.
 */

#ifndef ASM_BSEARCH_FINDMATCH
long binary_search_findmatch(t_encoder_context *context, long BufPos)
{
    ulong       ptr;
    ulong       a, b;
    ulong       *small_ptr, *big_ptr;
    ulong       end_pos;
    int         val; /* must be signed */
    int         bytes_to_boundary;
    int         clen;
    int         same;
    int         match_length;
    int         small_len, big_len;
    int         i, best_repeated_offset;
    #ifdef MULTIPLE_SEARCH_TREES
    ushort      tree_to_use;

    /*
     * Retrieve root node of tree to search, and insert current node at
     * the root.
     */
    tree_to_use = *((ushort UNALIGNED *) &context->enc_MemWindow[BufPos]);

    ptr        = context->enc_tree_root[tree_to_use];
    context->enc_tree_root[tree_to_use] = BufPos;
    #else
    ptr = context->enc_single_tree_root;
    context->enc_single_tree_root = BufPos;
    #endif
    /*
     * end_pos is the furthest location back we will search for matches
     *
     * Remember that our window size is reduced by 3 bytes because of
     * our repeated offset codes.
     *
     * Since BufPos starts at context->enc_window_size when compression begins,
     * end_pos will never become negative.
     */
    end_pos = BufPos - (context->enc_window_size-4);

    /*
     * Root node is either NULL, or points to a really distant position.
     */
    if (ptr <= end_pos)
        {
        left[BufPos] = right[BufPos] = 0;
        return 0;
        }

    #ifdef MULTIPLE_SEARCH_TREES
    /*
     * confirmed length (no need to check the first clen chars in a search)
     *
     * note: clen is always equal to min(small_len, big_len)
     */
    clen            = 2;

    /*
     * current best match length
     */
    match_length    = 2;

    /*
     * longest match which is < our string
     */
    small_len       = 2;

    /*
     * longest match which is > our string
     */
    big_len         = 2;

    /*
     * record match position for match length 2
     */
    context->enc_matchpos_table[2] = BufPos - ptr + 2;

        #ifdef VERIFY_SEARCHES
    VERIFY_MULTI_TREE_SEARCH_CODE("binary_search_findmatch()");
        #endif

    #else /* !MULTIPLE_SEARCH_TREES */

    clen            = 0;
    match_length    = 0;
    small_len       = 0;
    big_len         = 0;

    #endif /* MULTIPLE_SEARCH_TREES */

    /*
     * pointers to nodes to check
     */
    small_ptr             = &left[BufPos];
    big_ptr               = &right[BufPos];

    do
        {
        /* compare bytes at current node */
        same = clen;

    #ifdef VERIFY_SEARCHES
        VERIFY_SEARCH_CODE("binary_search_findmatch()")
    #endif

        /* don't need to check first clen characters */
        a    = ptr + clen;
        b    = BufPos + clen;

        while ((val = ((int) context->enc_MemWindow[a++]) - ((int) context->enc_MemWindow[b++])) == 0)
            {
            /* don't exceed MAX_MATCH */
            if (++same >= MAX_MATCH)
                goto long_match;
            }

        if (val < 0)
            {
            if (same > big_len)
                {
                if (same > match_length)
                    {
                    long_match:
                    do
                        {
                        context->enc_matchpos_table[++match_length] = BufPos-ptr+(NUM_REPEATED_OFFSETS-1);
                        } while (match_length < same);

                    if (same >= BREAK_LENGTH)
                        {
                        *small_ptr = left[ptr];
                        *big_ptr   = right[ptr];
                        goto end_bsearch;
                        }
                    }

                big_len = same;
                clen = min(small_len, big_len);
                }

            *big_ptr = ptr;
            big_ptr  = &left[ptr];
            ptr      = *big_ptr;
            }
        else
            {
            if (same > small_len)
                {
                if (same > match_length)
                    {
                    do
                        {
                        context->enc_matchpos_table[++match_length] = BufPos-ptr+(NUM_REPEATED_OFFSETS-1);
                        } while (match_length < same);

                    if (same >= BREAK_LENGTH)
                        {
                        *small_ptr = left[ptr];
                        *big_ptr   = right[ptr];
                        goto end_bsearch;
                        }
                    }

                small_len = same;
                clen = min(small_len, big_len);
                }

            *small_ptr = ptr;
            small_ptr  = &right[ptr];
            ptr        = *small_ptr;
            }
        } while (ptr > end_pos); /* while we don't go too far backwards */

    *small_ptr = 0;
    *big_ptr   = 0;


    end_bsearch:

    /*
     * If we have multiple search trees, we are already guaranteed
     * a minimum match length of 2 when we reach here.
     *
     * If we only have one tree, then we're not guaranteed anything.
     */
    #ifndef MULTIPLE_SEARCH_TREES
    if (match_length < MIN_MATCH)
        return 0;
    #endif

    /*
     * Check to see if any of our match lengths can
     * use repeated offsets.
     */

    /*
     * repeated offset 1
     */
    for (i = 0; i < match_length; i++)
        {
        if (context->enc_MemWindow[BufPos+i] != context->enc_MemWindow[BufPos-context->enc_last_matchpos_offset[0]+i])
            break;
        }

    /*
     * the longest repeated offset
     */
    best_repeated_offset = i;

    if (i >= MIN_MATCH)
        {
        /*
         * Yes, we can do a repeated offset for some match lengths; replace
         * their positions with the repeated offset position
         */
        do
            {
            context->enc_matchpos_table[i] = 0; /* first repeated offset position */
            } while (--i >= MIN_MATCH);

        /* A speed optimization to cope with long runs of bytes */
        if (best_repeated_offset > BREAK_LENGTH)
            goto quick_return;
        }

    /*
     * repeated offset 2
     */
    for (i = 0; i < match_length; i++)
        {
        if (context->enc_MemWindow[BufPos+i] != context->enc_MemWindow[BufPos-context->enc_last_matchpos_offset[1]+i])
            break;
        }

    /*
     * Does the second repeated offset provide a longer match?
     *
     * If so, leave the first repeated offset alone, but fill out the
     * difference in match lengths in the table with repeated offset 1.
     */
    if (i > best_repeated_offset)
        {
        do
            {
            context->enc_matchpos_table[++best_repeated_offset] = 1;
            } while (best_repeated_offset < i);
        }

    /*
     * repeated offset 3
     */
    for (i = 0; i < match_length; i++)
        {
        if (context->enc_MemWindow[BufPos+i] != context->enc_MemWindow[BufPos-context->enc_last_matchpos_offset[2]+i])
            break;
        }

    /*
     * Does the third repeated offset provide a longer match?
     */
    if (i > best_repeated_offset)
        {
        do
            {
            context->enc_matchpos_table[++best_repeated_offset] = 2;
            } while (best_repeated_offset < i);
        }

    quick_return:

    /*
     * Don't let a match cross a 32K boundary
     */
    bytes_to_boundary = (CHUNK_SIZE-1) - ((int) BufPos & (CHUNK_SIZE-1));

    if (match_length > bytes_to_boundary)
        {
        match_length = bytes_to_boundary;

        if (match_length < MIN_MATCH)
            match_length = 0;
        }

    return (long) match_length;
}
#endif


/*
 * Inserts the string at the current BufPos into the tree.
 *
 * Does not record all the best match lengths or otherwise attempt
 * to search for matches
 *
 * Similar to the above function.
 */
#ifndef ASM_QUICK_INSERT_BSEARCH_FINDMATCH
void quick_insert_bsearch_findmatch(t_encoder_context *context, long BufPos, long end_pos)
{
    long        ptr;
    ulong       a,b;
    ulong       *small_ptr, *big_ptr;
    int         val;
    int         small_len, big_len;
    int         same;
    int         clen;
    #ifdef MULTIPLE_SEARCH_TREES
    ushort      tree_to_use;

    tree_to_use = *((ushort UNALIGNED *) &context->enc_MemWindow[BufPos]);
    ptr        = context->enc_tree_root[tree_to_use];
    context->enc_tree_root[tree_to_use] = BufPos;
    #else
    ptr = context->enc_single_tree_root;
    context->enc_single_tree_root = BufPos;
    #endif

    if (ptr <= end_pos)
        {
        left[BufPos] = right[BufPos] = 0;
        return;
        }

    #ifdef MULTIPLE_SEARCH_TREES
    clen            = 2;
    small_len       = 2;
    big_len         = 2;

        #ifdef VERIFY_SEARCHES
    VERIFY_MULTI_TREE_SEARCH_CODE("quick_insert_bsearch_findmatch()");
        #endif

    #else
    clen            = 0;
    small_len       = 0;
    big_len         = 0;
    #endif

    small_ptr       = &left[BufPos];
    big_ptr         = &right[BufPos];

    do
        {
        _ASSERTE ((ulong) ptr >= (ulong) (context->enc_RealLeft - context->enc_Left));

        same = clen;

        a    = ptr+clen;
        b    = BufPos+clen;

    #ifdef VERIFY_SEARCHES
        VERIFY_SEARCH_CODE("quick_insert_bsearch_findmatch()")
    #endif

        while ((val = ((int) context->enc_MemWindow[a++]) - ((int) context->enc_MemWindow[b++])) == 0)
            {
            /*
             * Here we break on BREAK_LENGTH, not MAX_MATCH
             */
            if (++same >= BREAK_LENGTH)
                break;
            }

        if (val < 0)
            {
            if (same > big_len)
                {
                if (same >= BREAK_LENGTH)
                    {
                    *small_ptr = left[ptr];
                    *big_ptr = right[ptr];
                    return;
                    }

                big_len = same;
                clen = min(small_len, big_len);
                }

            *big_ptr = ptr;
            big_ptr  = &left[ptr];
            ptr      = *big_ptr;
            }
        else
            {
            if (same > small_len)
                {
                if (same >= BREAK_LENGTH)
                    {
                    *small_ptr = left[ptr];
                    *big_ptr = right[ptr];
                    return;
                    }

                small_len = same;
                clen = min(small_len, big_len);
                }

            *small_ptr = ptr;
            small_ptr  = &right[ptr];
            ptr        = *small_ptr;
            }
        } while (ptr > end_pos);

    *small_ptr = 0;
    *big_ptr   = 0;
}
#endif


/*
 * Remove a node from the search tree; this is ONLY done for the last
 * BREAK_LENGTH symbols (see optenc.c).  This is because we will have
 * inserted strings that contain undefined data (e.g. we're at the 4th
 * last byte from the file and binary_search_findmatch() a string into
 * the tree - everything from the 4th symbol onwards is invalid, and
 * would cause problems if it remained in the tree, so we have to
 * remove it).
 */
void binary_search_remove_node(t_encoder_context *context, long BufPos, ulong end_pos)
{
    ulong   ptr;
    ulong   left_node_pos;
    ulong   right_node_pos;
    ulong   *link;
#ifdef MULTIPLE_SEARCH_TREES
    ushort  tree_to_use;

    /*
     * The root node of tree_to_use should equal BufPos, since that is
     * the most recent insertion into that tree - but if we never
     * inserted this string (because it was a near match or a long
     * string of zeroes), then we can't remove it.
     */
    tree_to_use = *((ushort UNALIGNED *) &context->enc_MemWindow[BufPos]);


    /*
     * If we never inserted this string, do not attempt to remove it
     */

    if (context->enc_tree_root[tree_to_use] != (ulong) BufPos)
        return;

    link = &context->enc_tree_root[tree_to_use];
#else
    if (context->enc_single_tree_root != (ulong) BufPos)
        return;

    link = &context->enc_single_tree_root;
#endif

    /*
     * If the last occurence was too far away
     */
    if (*link <= end_pos)
        {
        *link = 0;
        left[BufPos] = right[BufPos] = 0;
        return;
        }

    /*
     * Most recent location of these chars
     */
    ptr             = BufPos;

    /*
     * Most recent location of a string which is "less than" it
     */
    left_node_pos   = left[ptr];

    if (left_node_pos <= end_pos)
        left_node_pos = left[ptr] = 0;

    /*
     * Most recent location of a string which is "greater than" it
     */
    right_node_pos  = right[ptr];

    if (right_node_pos <= end_pos)
        right_node_pos = right[ptr] = 0;

    while (1)
        {
#ifdef VERIFY_SEARCHES
        _ASSERTE (left_node_pos < (ulong) BufPos);
        _ASSERTE (right_node_pos < (ulong) BufPos);
#endif

        /*
         * If left node position is greater than right node position
         * then follow the left node, since that is the more recent
         * insertion into the tree.  Otherwise follow the right node.
         */
        if (left_node_pos > right_node_pos)
            {
            /*
             * If it's too far away, then store that it never happened
             */
            if (left_node_pos <= end_pos)
                left_node_pos = 0;

            ptr = *link = left_node_pos;

            if (!ptr)
                break;

            left_node_pos   = right[ptr];
            link            = &right[ptr];
            }
        else
            {
            /*
             * If it's too far away, then store that it never happened
             */
            if (right_node_pos <= end_pos)
                right_node_pos = 0;

            ptr = *link = right_node_pos;

            if (!ptr)
                break;

            right_node_pos  = left[ptr];
            link            = &left[ptr];
            }
        }
}