/* ecc Version 1.2 by Paul Flaherty (paulf at stanford.edu) Copyright (C) 1993 Free Software Foundation, Inc. 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 2, 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, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ /* gflib.c Math Library for GF[256] This file contains a number of mathematical functions for GF[256]. Entry and result are always assumed to be in vector notation, since said notation allows for the zero element. Attempting to reciprocate the zero element results in process exit 42. */ #include "gf.h" /* Multiply two field elements */ unsigned char gfmul (mul1, mul2) unsigned char mul1, mul2; { unsigned char mul3; if (mul1 == 0 || mul2 == 0) mul3 = 0; else mul3 = e2v[(v2e[mul1] + v2e[mul2]) % 255]; return (mul3); } /* Add two field elements. Subtraction and addition are equivalent */ unsigned char gfadd (add1, add2) unsigned char add1, add2; { unsigned char add3; add3 = add1 ^ add2; return (add3); } /* Invert a field element, for division */ unsigned char gfinv (ivt) unsigned char ivt; { unsigned char ivtd; if (ivt == 0) exit (42); ivtd = e2v[255 - v2e[ivt]]; return (ivtd); } /* Exponentiation. Convert to exponential notation, mod 255 */ unsigned char gfexp (mant, powr) unsigned char mant, powr; { unsigned char expt; if (mant == 0) expt = 0; else expt = e2v[(v2e[mant] * powr) % 255]; return (expt); }
file: /Techref/method/error/rs-255-248-7-pf-1993/gflib_c.htm, 7KB, , updated: 2000/5/10 13:17, local time: 2024/8/14 20:18,
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