diff --git a/src/filter/sub.hh b/src/filter/sub.hh
new file mode 100644
index 00000000..e188bf5a
--- /dev/null
+++ b/src/filter/sub.hh
@@ -0,0 +1,87 @@
+/* sub.hh -- simple delta filter
+
+   This file is part of the UPX executable compressor.
+
+   Copyright (C) 1996-2001 Markus Franz Xaver Johannes Oberhumer
+   Copyright (C) 1996-2001 Laszlo Molnar
+   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.com      ml1050@cdata.tvnet.hu
+ */
+
+
+
+/*************************************************************************
+//
+**************************************************************************/
+
+#define SUB(f, N, T, get, set) \
+    upx_byte *b = f->buf; \
+    unsigned l = f->buf_len / sizeof(T); \
+    int i; \
+    T d[N]; \
+    \
+    i = N - 1; do d[i] = 0; while (--i >= 0); \
+    \
+    i = N - 1; \
+    do { \
+        T delta = get(b) - d[i]; \
+        set(b, delta); \
+        d[i] += delta; \
+        b += sizeof(T); \
+        if (--i < 0) \
+            i = N - 1; \
+    } while (--l > 0); \
+    f->calls = (f->buf_len / sizeof(T)) - N; \
+    assert((int)f->calls > 0); \
+    return 0;
+
+
+#define ADD(f, N, T, get, set) \
+    upx_byte *b = f->buf; \
+    unsigned l = f->buf_len / sizeof(T); \
+    int i; \
+    T d[N]; \
+    \
+    i = N - 1; do d[i] = 0; while (--i >= 0); \
+    \
+    i = N - 1; \
+    do { \
+        d[i] += get(b); \
+        set(b, d[i]); \
+        b += sizeof(T); \
+        if (--i < 0) \
+            i = N - 1; \
+    } while (--l > 0); \
+    f->calls = (f->buf_len / sizeof(T)) - N; \
+    assert((int)f->calls > 0); \
+    return 0;
+
+
+#define SCAN(f, N, T, get, set) \
+    f->calls = (f->buf_len / sizeof(T)) - N; \
+    assert((int)f->calls > 0); \
+    return 0;
+
+
+
+/*
+vi:ts=4:et:nowrap
+*/
+