windows-server-2003/base/mspatch/lzx/decoder/maketbl.c

/*
 * Table-building routines
 *
 * make_table() is based on ** Public Domain ** source "AR001.ZIP".
 */

#include <memory.h>
#pragma intrinsic(memset)

#include "decoder.h"


/*
 * Make a decoding table for decoding nchar possible Huffman elements
 * with bit lengths given by bitlen.
 *
 * Output the main lookup table into table[] and use leftright[] for
 * supplementary information (for bitlengths > tablebits).
 *
 * The size of table[] is tablebits elements.
 */
#ifndef ASM_MAKE_TABLE
bool NEAR __cdecl make_table(
        t_decoder_context       *context,
        int                             nchar,
        const byte                      *bitlen,
        byte                            tablebits,
        short                           *table,
        short                           *leftright
)
{
    uint    i;
        int             ch;
    short * p;
    uint    count[17], weight[17], start[18];
    int     avail;
    uint    nextcode;
    uint    k;
        byte    len;
        byte    jutbits;

        for (i = 1; i <= 16; i++)
                count[i] = 0;

        /* count the number of elements of each bit length */
    for (i = 0; i < (uint) nchar; i++)
                count[bitlen[i]]++;

        start[1] = 0;

        for (i = 1; i <= 16; i++)
                start[i + 1] = start[i] + (count[i] << (16 - i));

#ifdef BIT16
    if (start[17])
    {
        return false; /* bad table */
    }
#else
    if (start[17] != 65536)
    {
        if (start[17] == 0)
        {
            /*
             * All elements are length zero
             */
            memset(table, 0, sizeof(ushort)*(1 << tablebits));
            return true; /* success */
        }
        else
        {
            return false; /* bad table */
        }
    }
#endif

        jutbits = 16 - tablebits;

        for (i = 1; i <= tablebits; i++)
        {
                start[i] >>= jutbits;
                weight[i] = 1 << (tablebits - i);
        }

        while (i <= 16)
        {
                weight[i] = 1 << (16 - i);
                i++;
        }

        i = start[tablebits+1] >> jutbits;

#ifdef BIT16
    if (i)
#else
        if (i != 65536)
#endif
        {
                memset(
            &table[i],
            0,
            sizeof(ushort)*((1 << tablebits)-i)
        );
        }

        avail = nchar;

        for (ch = 0; ch < nchar; ch++)
        {
                if ((len = bitlen[ch]) == 0)
                        continue;

                nextcode = start[len] + weight[len];

                if (len <= tablebits)
                {
            if (nextcode > (uint) (1 << tablebits))
                return false; /* bad table */

                        for (i = start[len]; i < nextcode; i++)
                                table[i] = (short)ch;

                        start[len] = nextcode;
                }
                else
                {
                        byte bi;

                        k = start[len];
                        start[len] = nextcode;
                        p = &table[k >> jutbits];

                        bi = len - tablebits;
                        k <<= tablebits;

                        do
                        {
                                if (*p == 0)
                                {
                                        leftright[avail*2] = leftright[avail*2+1] = 0;
                                        *p = (short) -avail;
                                        avail++;
                                }

                                if ((signed short) k < 0) // if (k & 32768)
                                        p = &leftright[-(*p)*2+1];
                                else
                                        p = &leftright[-(*p)*2];

                                k <<= 1;
                                bi--;
                        } while (bi);

                        *p = (short)ch;
                }
        }

    return true;
}
#endif


/*
 * Specialised make table routine where it is known that there are
 * only 8 elements (nchar=8) and tablebits=7 (128 byte lookup table).
 *
 * Since there can be no overflow, this will be a direct lookup.
 *
 * Important difference; the lookup table returns a byte, not a ushort.
 */
bool NEAR make_table_8bit(t_decoder_context *context, byte bitlen[], byte table[])
{
        ushort count[17], weight[17], start[18];
        ushort i;
        ushort nextcode;
        byte   len;
        byte   ch;

        for (i = 1; i <= 16; i++)
                count[i] = 0;

        for (i = 0; i < 8; i++)
                count[bitlen[i]]++;

        start[1] = 0;

        for (i = 1; i <= 16; i++)
                start[i + 1] = start[i] + (count[i] << (16 - i));

        if (start[17] != 0)
        return false; /* bad table */

        for (i = 1; i <= 7; i++)
        {
                start[i] >>= 9;
                weight[i]  = 1 << (7 - i);
        }

        while (i <= 16)
        {
                weight[i] = 1 << (16 - i);
                i++;
        }

        memset(table, 0, 1<<7);

        for (ch = 0; ch < 8; ch++)
        {
                if ((len = bitlen[ch]) == 0)
                        continue;

                nextcode = start[len] + weight[len];

                if (nextcode > (1 << 7))
            return false; /* bad table */

                for (i = start[len]; i < nextcode; i++)
                        table[i] = ch;

                start[len] = nextcode;
        }

    return true;
}