LZO Decompress

gistfile1.c

LZO_PUBLIC(int)
lzo1_decompress  ( const lzo_bytep in , lzo_uint  in_len,
                         lzo_bytep out, lzo_uintp out_len,
                         lzo_voidp wrkmem )
{
    lzo_bytep op;
    const lzo_bytep ip;
    const lzo_bytep const ip_end = in + in_len;
    lzo_uint t;

    LZO_UNUSED(wrkmem);

    op = out;
    ip = in;
    while (ip < ip_end)
    {
        t = *ip++;  /* get marker */

        if (t < R0MIN)          /* a literal run */
        {
            if (t == 0)             /* a R0 literal run */
            {
                t = *ip++;
                if (t >= R0FAST - R0MIN)            /* a long R0 run */
                {
                    t -= R0FAST - R0MIN;
                    if (t == 0)
                        t = R0FAST;
                    else
                    {
#if 0
                        t = 256u << ((unsigned) t);
#else
                        /* help the optimizer */
                        lzo_uint tt = 256;
                        do tt <<= 1; while (--t > 0);
                        t = tt;
#endif
                    }
                    MEMCPY8_DS(op,ip,t);
                    continue;
                }
                t += R0MIN;
            }
            MEMCPY_DS(op,ip,t);
        }
        else                    /* a match */
        {
            lzo_uint tt;
            /* get match offset */
            const lzo_bytep m_pos = op - 1;
            m_pos -= (lzo_uint)(t & OMASK) | (((lzo_uint) *ip++) << OBITS);

            /* get match len */
            if (t >= ((MSIZE - 1) << OBITS))                /* all m-bits set */
                tt = (MIN_MATCH_LONG - THRESHOLD) + *ip++;  /* a long match */
            else
                tt = t >> OBITS;                            /* a short match */

            assert(m_pos >= out);
            assert(m_pos <  op);
            /* a half unrolled loop */
            *op++ = *m_pos++;
            *op++ = *m_pos++;
            MEMCPY_DS(op,m_pos,tt);
        }
    }

    *out_len = pd(op, out);

    /* the next line is the only check in the decompressor ! */
    return (ip == ip_end ? LZO_E_OK :
           (ip < ip_end  ? LZO_E_INPUT_NOT_CONSUMED : LZO_E_INPUT_OVERRUN));
}