41 lines
1.0 KiB
C
41 lines
1.0 KiB
C
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/* gf256mul.c */
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/*
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This file is part of the ARM-Crypto-Lib.
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Copyright (C) 2006-2010 Daniel Otte (daniel.otte@rub.de)
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <stdint.h>
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uint8_t gf256mul(uint8_t a, uint8_t b, uint8_t reducer){
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uint8_t r=0;
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while(a&0xFE){
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if(a&1){
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r ^= b;
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}
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a >>= 1;
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if(b&0x80){
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b <<= 1;
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b ^= reducer;
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}else{
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b <<= 1;
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}
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}
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if(a&1){
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r ^= b;
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}
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return r;
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}
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