ported ulmCipherOps.Mod

Former-commit-id: 2a16fd9af7

src/lib/ulm/ulmCipherOps.Mod

@@ -0,0 +1,67 @@
+(* Ulm's Oberon Library
+   Copyright (C) 1989-1997 by University of Ulm, SAI, D-89069 Ulm, Germany
+   ----------------------------------------------------------------------------
+   Ulm's Oberon Library is free software; you can redistribute it
+   and/or modify it under the terms of the GNU Library General Public
+   License as published by the Free Software Foundation; either version
+   2 of the License, or (at your option) any later version.
+
+   Ulm's Oberon Library 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
+   Library General Public License for more details.
+
+   You should have received a copy of the GNU Library General Public
+   License along with this library; if not, write to the Free Software
+   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+   ----------------------------------------------------------------------------
+   E-mail contact: oberon@mathematik.uni-ulm.de
+   ----------------------------------------------------------------------------
+   $Id: CipherOps.om,v 1.1 1997/04/02 11:53:20 borchert Exp borchert $
+   ----------------------------------------------------------------------------
+   $Log: CipherOps.om,v $
+   Revision 1.1  1997/04/02  11:53:20  borchert
+   Initial revision
+
+   ----------------------------------------------------------------------------
+*)
+
+MODULE ulmCipherOps; (* Michael Szczuka *)
+
+   (* useful functions for stream ciphers *)
+
+   IMPORT Streams := ulmStreams, SYS := SYSTEM, Write := ulmWrite;
+
+   PROCEDURE XorByte* (b1, b2: SYS.BYTE) : SYS.BYTE;
+      (* adds two bytes bitwise modulo 2 *)
+   BEGIN
+      RETURN SYS.VAL(SYS.BYTE, SYS.VAL(SET, b1) / SYS.VAL(SET, b2))
+   END XorByte;
+
+   PROCEDURE XorStream* (in1, in2, out: Streams.Stream; 
+			length: INTEGER) : BOOLEAN;
+      (* adds two streams bitwise modulo 2; restricted to length bytes *)
+      VAR
+	 b1, b2, res : SYS.BYTE;
+	 wholeStream : BOOLEAN;
+   BEGIN
+      IF length < 0 THEN
+	 wholeStream := TRUE;
+      ELSE
+	 wholeStream := FALSE;
+      END;
+      WHILE wholeStream OR (length > 0) DO
+	 IF Streams.ReadByte(in1, b1) & Streams.ReadByte(in2, b2) THEN
+	    res := XorByte(b1, b2);
+	    IF ~Streams.WriteByte(out, res) THEN
+	       RETURN FALSE
+	    END;
+	 ELSE
+	    RETURN wholeStream
+	 END;
+	 DEC(length);
+      END;
+      RETURN TRUE
+   END XorStream;
+
+END ulmCipherOps.