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+/* filter.h --
+
+   This file is part of the UPX executable compressor.
+
+   Copyright (C) 1996-2000 Markus Franz Xaver Johannes Oberhumer
+   Copyright (C) 1996-2000 Laszlo Molnar
+
+   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
+ */
+
+
+#ifndef __UPX_FILTER_H
+#define __UPX_FILTER_H
+
+class Filter;
+class FilterImp;
+
+
+/*************************************************************************
+// A filter is a reversible operation that modifies a given
+// block of memory.
+//
+// A filter can fail and return false. In this case the buffer
+// must be unmodified (or otherwise restored).
+//
+// If a filter fails and somehow cannot restore the block it must
+// call throwFilterException() - this will cause the compression
+// to fail.
+//
+// The return value of unfilters can/should be ignored. They throw
+// exceptions in case of errors.
+//
+// The main idea behind filters is to convert relative jumps and calls
+// to absolute addresses so that the buffer compresses better.
+**************************************************************************/
+
+class Filter
+{
+public:
+    Filter(int level) { clevel = level; init(); }
+    void init(int id=0, unsigned addvalue=0);
+
+    bool filter(upx_byte *buf, unsigned buf_len);
+    bool unfilter(upx_byte *buf, unsigned buf_len, bool verify_checksum=false);
+    bool verifyUnfilter();
+    bool scan(const upx_byte *buf, unsigned buf_len);
+
+public:
+    // Will be set by each call to filter()/unfilter().
+    // Read-only afterwards.
+    upx_byte *buf;
+    unsigned buf_len;
+
+    // Checksum of the buffer before applying the filter
+    // or after un-applying the filter.
+    unsigned adler;
+
+    // Input parameters used by various filters.
+    unsigned addvalue;
+    int forced_cto;
+    const int *preferred_ctos;
+
+    // Input/output parameters used by various filters
+    unsigned char cto;              // call trick offset
+
+    // Output used by various filters. Read only.
+    unsigned calls;
+    unsigned noncalls;
+    unsigned wrongcalls;
+    unsigned lastcall;
+
+    // Read only.
+    int id;
+
+private:
+    int clevel;         // compression level
+};
+
+
+/*************************************************************************
+// We don't want a full OO interface here because of
+// certain implementation speed reasons.
+//
+// This class is strictly private to Filter - don't look.
+**************************************************************************/
+
+class FilterImp
+{
+    friend class Filter;
+
+private:
+    struct f_t {
+        int id;
+        unsigned min_buf_len;
+        unsigned max_buf_len;
+        int (*f)(Filter *);
+        int (*u)(Filter *);
+        int (*s)(Filter *);
+    };
+    static const f_t filters[];
+    static const int n_filters;
+
+    static const f_t *getFilter(int id);
+};
+
+
+#endif /* already included */
+
+
+/*
+vi:ts=4:et
+*/
+