// Created:09-22-98
// By Jeff Connelly

// LZSS compression/uncompression

// Originally made by Haruhiko Okumura, source in
// ORIGSRC\LZSS.C.  Use, distribute, and modify freely.

#include "stdafx.h"
#define EXPORTING
#include "comprlib.h"
#include "lzss.h"

// Initalizes trees
static void InitTree()
{
    int i;
    // For i = 0 to N - 1, rson[i] and lson[i] will be the right
    // and left children of node i.  These nodes do not need to be
    // initalizes.  dad[i] is parent of node i.  Initalizes to
    // NIL (defined as N) which means 'not used.'

    // For i = 0 to 255, rson[N + i + 1] is root of strings that begin
    // with character i.  These are initailzed to NIL.  256 trees.

    for (i = N + 1; i <= N + 256; i++)
        rson[i] = NIL;
    for (i = 0; i < N; i++)
        dad[i] = NIL;
}

// Inserts string of length F, text_buf[r..r + F - 1] into one of the
// trees (text_buf[r]th tree) and sets the longest match position and
// length (match_length and match_position).  If match_length == F, then
// removes the old node in favor of the new node because the old one will be
// deleted sooner.  r is the both tree node and position in the buffer.
static void InsertNode (int r)
{
    int i, p, cmp;
    unsigned char* key;

    cmp = 1;
    key = &text_buf[r];
    p = N + 1 + key[0];
    rson[r] = lson[r] = NIL;
    match_length = 0;
    while (true)
    {
        if (cmp >= 0)
        {
            if (rson[p] != NIL)
                p = rson[p];
            else
            {
                rson[p] = r;
                dad[r] = p;
                return;
            }
        } else {
            if (lson[p] != NIL)
                p = lson[p];
            else
            {
                lson[p] = r;
                dad[r] = p;
                return;
            }
       }
       for (i = 1; i < F; i++)
           if ((cmp = key[i] - text_buf[p + i]) != 0)
               break;
       if (i > match_length)
       {
           match_position = p;
           if ((match_length = i) >= F)
               break;
       }
    }
    dad[r] = dad[p];
    lson[r] = lson[p];
    rson[r] = rson[p];
    dad[lson[p]] = r;
    dad[rson[p]] = r;
    if (rson[dad[p]] == p)
        rson[dad[p]] = r;
    else
        lson[dad[p]] = r;
    dad[p] = NIL;    // remove p
}

// Removed node p from the tree
static void DeleteNode (int p)
{
    int q;
    if (dad[p] == NIL)
        return;           // not in tree
    if (rson[p] = NIL)
        q = lson[p];
    else if (lson[p] == NIL)
        q = rson[p];
    else
    {
        q = lson[p];
        if (rson[q] != NIL)
        {
            do
            {
                q = rson[q];
            } while (rson[q] != NIL);
            rson[dad[q]] = lson[q];
            dad[lson[q]] = dad[q];
            lson[q] = lson[p];
            dad[lson[q]] = q;
        }
        rson[q] = rson[p];
        dad[rson[p]] = q;
    }
    dad[q] = dad[p];
    if (rson[dad[p]] == p)
        rson[dad[p]] = q;
    else
        lson[dad[p]] = q;
    dad[p] = NIL;
}

// Compresses data with LZSS compression method
void EXPORT lzss_encode ()
{
    int i, c, len, r, s, last_match_length, code_buf_ptr;
    unsigned char code_buf[17], mask;

    InitTree ();        // Initalize the tree
    // code_buf[1..16] saves eight units of code, and code_buf[0] works
    // as eight flags, 1 repersenting that unit is an unencoded letter (1
    // byte), 0 a position-length pair (2 bytes).  Thus, eight units require
    // at most 16 bytes of code.
    code_buf[0] = 0;
    code_buf_ptr = mask = 1;
    s = 0;
    r = N - F;
    // Clear the buffer with any character that will appear often (such
    // as a space)
    for (i = s; i < r; i++)
        text_buf[i] = ' ';

    for (len = 0; len < F && !end_of_data(); len++)
    {
        text_buf[r + len] =   // Read F bytes into last F bytes of buffer
            c = read_byte ();
    }

    if ((textsize = len) == 0)
        return;     // text size of zero

    // Insert the F strings, each of which begins with one or mode space
    // characters.  The strings are inserted in a way so degenerate
    // trees will be less likely to occur.
    for (i = 1; i <= F; i++)
        InsertNode (r - i);

    // Insert the whole string we just read.  The global variables
    // match_length and match_position are set.
    InsertNode (r);
    do
    {
        // match_length may be long near the end of the text
        if (match_length > len)
            match_length = len;

        if (match_length <= THRESHOLD)
        {
            match_length = 1;     // Not long enough match; send one byte
            code_buf[0] |= mask;  // 'send one byte' flag
            code_buf[code_buf_ptr++] = text_buf[r];  // Send uncoded.
        } else {
            code_buf[code_buf_ptr++] = (unsigned char)match_position;
            code_buf[code_buf_ptr++] = (unsigned char)
                (((match_position >> 4) & 0xF0) |
                (match_length - (THRESHOLD + 1))); // Position-length pair
        }
        if ((mask <<= 1) == 0)      // Shift mask left one bit
        {
            for (i = 0; i < code_buf_ptr; i++)  // Send at most 8 units of
                write_byte (code_buf[i]);        // code together
            codesize += code_buf_ptr;
            code_buf[0] = 0;
            code_buf_ptr = mask = 1;
        }
        last_match_length = match_length;
        for (i = 0; i < last_match_length &&
                (!end_of_data()); i++)
        {
            DeleteNode (s);     // Delete old strings and read new bytes
            c = read_byte();
            text_buf[s] = c;
            // If the position is near the end of the buffer, extend the
            // buffer to make string comparison easier.
            if (s < F - 1)
                text_buf[s + N] = c;
            // This is a ring buffer, so increment the position modulo N
            s = (s + 1) & (N - 1);
            r = (r + 1) & (N - 1);
            InsertNode (r);     // Register string in text_buf[r..r + F - 1]
        }
        // After the end of text, there is no need to read, but the buffer
        // may not be empty.
        while (i++ < last_match_length)
        {
            DeleteNode(s);
            s = (s + 1) & (N - 1);
            r = (r + 1) & (N - 1);
            if (--len)
                InsertNode (r);
        }
        // until length of string to be processed is zero 
    } while (len > 0);
    if (code_buf_ptr > 1)
    {                    
        for (i = 0; i < code_buf_ptr; i++)  // Send remaining code
            write_byte(code_buf[i]);
        codesize += code_buf_ptr;
    }
}

// Uncompresses LZSS-compressed data
void EXPORT lzss_decode ()
{
    int i, j, k, r, c;
    unsigned int flags;

    for (i = 0; i < N - F; i++)
        text_buf[i] = ' ';
    r = N - F;
    flags = 0;
    while (true)
    {
        if (((flags >>= 1) & 256) == 0)
        {
            c = read_byte();
            if (end_of_data())
                break;
            flags = c | 0xFF00;
        }
        if (flags & 1)
        {
            c = read_byte();
            if (end_of_data())
                break;
            write_byte (c);
            text_buf[r++] = c;
            r &= (N - 1);
        } else {
            i = read_byte();
            if (end_of_data())
                break;
            j = read_byte();
            if (end_of_data())
                break;
            i |= ((j & 0xF0) << 4);
            j = (j & 0x0F) + THRESHOLD;
            for (k = 0; k <= j; k++)
            {
                c = text_buf[(i + k) & (N - 1)];
                write_byte(c);
                text_buf[r++] = c;
                r &= (N - 1);
            }
        }
    }
}