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typedef struct Thwack           Thwack;
typedef struct Unthwack         Unthwack;
typedef struct ThwBlock         ThwBlock;
typedef struct UnthwBlock       UnthwBlock;

enum
{
        ThwStats        = 8,
        ThwMaxBlock     = 1600,         /* max size of compressible block */

        HashLog         = 12,
        HashSize        = 1<<HashLog,
        HashMask        = HashSize - 1,

        MinMatch        = 3,            /* shortest match possible */

        MaxOff          = 8,
        OffBase         = 6,

        MinDecode       = 8,            /* minimum bits to decode a match or lit; >= 8 */

        EWinBlocks      = 22,           /* blocks held in encoder window */
        DWinBlocks      = 32,           /* blocks held in decoder window */
        CompBlocks      = 10,           /* max blocks used to encode data */

        MaxSeqMask      = 8,            /* number of bits in coding block mask */
        MaxSeqStart     = 256           /* max offset of initial coding block */
};

struct ThwBlock
{
        ulong   seq;                    /* sequence number for this data */
        uchar   acked;                  /* ok to use this block; the decoder has it */
        ushort  begin;                  /* time of first byte in hash */
        uchar   *edata;                 /* last byte of valid data */
        ushort  maxoff;                 /* time of last valid hash entry */
        ushort  *hash;
        uchar   *data;
};

struct Thwack
{
        int             slot;           /* next block to use */
        ThwBlock        blocks[EWinBlocks];
        ushort          hash[EWinBlocks][HashSize];
        uchar           data[EWinBlocks][ThwMaxBlock];
};

struct UnthwBlock
{
        ulong   seq;                    /* sequence number for this data */
        ushort  maxoff;                 /* valid data in each block */
        uchar   *data;
};

struct Unthwack
{
        int             slot;           /* next block to use */
        UnthwBlock      blocks[DWinBlocks];
        uchar           data[DWinBlocks][ThwMaxBlock];
};

void    thwackinit(Thwack*);
void    unthwackinit(Unthwack*);
int     thwack(Thwack*, uchar *dst, uchar *src, int nsrc, ulong seq, ulong stats[ThwStats]);
void    thwackack(Thwack*, ulong seq, ulong mask);
int     unthwack(Unthwack*, uchar *dst, int ndst, uchar *src, int nsrc, ulong seq);
ulong   unthwackstate(Unthwack *ut, uchar *mask);