X-Git-Url: https://git.cryptolib.org/?p=avr-crypto-lib.git;a=blobdiff_plain;f=mugi%2Fgf256mul.S;fp=mugi%2Fgf256mul.S;h=b269d3a4a1b760d2d372598bb0cbfdf87de1009c;hp=0000000000000000000000000000000000000000;hb=4f50c75ee5a6cc88bf7ea71957ed509e298e6c25;hpb=7701e318e4e2bac7f84dbf6e368f1501814948fc

diff --git a/mugi/gf256mul.S b/mugi/gf256mul.S
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+/* gf256mul.S */
+/*
+    This file is part of the AVR-Crypto-Lib.
+    Copyright (C) 2008  Daniel Otte (daniel.otte@rub.de)
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 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.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+/* 
+ * File:        gf256mul.S
+ * Author:      Daniel Otte
+ * Date:        2008-12-19
+ * License:     GPLv3 or later
+ * Description: peasant's algorithm for multiplication in GF(2^8)
+ * 
+ */
+
+#include <avr/io.h>
+#define OPTIMIZE_SMALL_A
+
+/*
+ * param a: r24
+ * param b: r22
+ * param reducer: r20
+ */
+A = 23
+B = 22
+P = 24
+.global gf256mul
+
+#ifdef OPTIMIZE_SMALL_A
+gf256mul:
+	mov A, r24
+	clr r24
+1:	
+	lsr A
+	breq 4f
+	brcc 2f
+	eor P, B
+2:
+	lsl B
+	brcc 3f
+	eor B, r20	
+3:
+	rjmp 1b
+4:
+	brcc 2f
+	eor P, B
+2:
+	ret
+
+#else
+
+gf256mul:
+	mov r21, r24
+	clr r24
+	ldi r25, 8
+1:	
+	lsr A
+	brcc 2f
+	eor P, B
+2:
+	lsl B
+	brcc 3f
+	eor B, r20	
+3:
+	dec r25
+	brne 1b
+	ret
+
+#endif