upx/src/fcto_ml3.ch

/* fctl_ml3.ch -- filter CTO implementation

   This file is part of the UPX executable compressor.

   Copyright (C) 1996-2000 Markus Franz Xaver Johannes Oberhumer
   Copyright (C) 1996-2000 Laszlo Molnar
   Copyright (C) 2000 John F. Reiser
   All Rights Reserved.

   UPX and the UCL library are free software; you can redistribute them
   and/or modify them under the terms of the GNU General Public License as
   published by the Free Software Foundation; either version 2 of
   the License, or (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; see the file COPYING.
   If not, write to the Free Software Foundation, Inc.,
   59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

   Markus F.X.J. Oberhumer                   Laszlo Molnar
   markus.oberhumer@jk.uni-linz.ac.at        ml1050@cdata.tvnet.hu
 */



/*************************************************************************
//
**************************************************************************/

static int F(Filter *f)
{
#ifdef U
    // filter
    upx_byte *b = f->buf;
    const unsigned addvalue = f->addvalue;
#else
    // scan
    const upx_byte *b = f->buf;
#endif
    const unsigned size = f->buf_len;

    unsigned ic, jc, kc;
    unsigned cto;
    unsigned char cto8;
    unsigned calls = 0, noncalls = 0, noncalls2 = 0;
    unsigned lastnoncall = size, lastcall = 0;

    // find a 16MB large empty address space
    if (f->forced_cto >= 0 && f->forced_cto <= 255)
        cto8 = (unsigned char) f->forced_cto;
    else
    {
        unsigned char buf[256];
        memset(buf,0,256);

#if 1
        for (ic = 0; ic < size - 5; ic++)
            if (COND(b,ic,lastcall) && get_le32(b+ic+1)+ic+1 >= size)
            {
                buf[b[ic+1]] |= 1;
            }
#else
        {
            int i = size - 6;
            do {
                if (COND(b,i,lastcall) && get_le32(b+i+1)+i+1 >= size)
                    buf[b[i+1]] |= 1;
            } while (--i >= 0);
        }
#endif

        ic = 256;
        if (f->preferred_ctos)
        {
            for (const int *pc = f->preferred_ctos; *pc >= 0; pc++)
            {
                if (buf[*pc & 255] == 0)
                {
                    ic = *pc & 255;
                    break;
                }
            }
        }
#if 0
        // just a test to see if certain ctos would improve compression
        if (ic >= 256)
            for (ic = 0; ic < 256; ic += 16)
                if (buf[ic] == 0)
                    break;
#endif
        if (ic >= 256)
            for (ic = 0; ic < 256; ic++)
                if (buf[ic] == 0)
                    break;
        if (ic >= 256)
            //throwCantPack("call trick problem");
            return -1;
        cto8 = (unsigned char) ic;
    }
    cto = (unsigned)cto8 << 24;

    for (ic = 0; ic < size - 5; ic++)
    {
        if (!COND(b,ic,lastcall))
            continue;
        jc = get_le32(b+ic+1)+ic+1;
        // try to detect 'real' calls only
        if (jc < size)
        {
#ifdef U
            set_be32(b+ic+1,jc+addvalue+cto);
#endif
            if (ic - lastnoncall < 5)
            {
                // check the last 4 bytes before this call
                for (kc = 4; kc; kc--)
                    if (COND(b,ic-kc,lastcall) && b[ic-kc+1] == cto8)
                        break;
                if (kc)
                {
#ifdef U
                    // restore original
                    set_le32(b+ic+1,jc-ic-1);
#endif
                    if (b[ic+1] == cto8)
                        return 1;           // fail - buffer not restored
                    lastnoncall = ic;
                    noncalls2++;
                    continue;
                }
            }
            calls++;
            ic += 4;
            lastcall = ic+1;
        }
        else
        {
            assert(b[ic+1] != cto8);        // this should not happen
            lastnoncall = ic;
            noncalls++;
        }
    }

    f->cto = cto8;
    f->calls = calls;
    f->noncalls = noncalls;
    f->lastcall = lastcall;

#ifdef TESTING
    printf("\ncalls=%d noncalls=%d noncalls2=%d text_size=%x calltrickoffset=%x\n",calls,noncalls,noncalls2,size,cto);
#endif
    return 0;
}


#ifdef U
static int U(Filter *f)
{
    upx_byte *b = f->buf;
    const unsigned size5 = f->buf_len - 5;
    const unsigned addvalue = f->addvalue;
    const unsigned cto = f->cto << 24;
    unsigned lastcall = 0;

    unsigned ic, jc;

    for (ic = 0; ic < size5; ic++)
        if (COND(b,ic,lastcall))
        {
            jc = get_be32(b+ic+1);
            if (b[ic+1] == f->cto)
            {
                set_le32(b+ic+1,jc-ic-1-addvalue-cto);
                f->calls++;
                ic += 4;
                f->lastcall = lastcall = ic+1;
            }
            else
                f->noncalls++;
        }
    return 0;
}
#endif


/*
vi:ts=4:et
*/