mathctx.c

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/*
This file is part of BitPunch
Copyright (C) 2014-2015 Frantisek Uhrecky <frantisek.uhrecky[what here]gmail.com>

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/>.
*/
#include "mathctx.h"
#include "gf2x.h"

#include <bitpunch/debugio.h>
#include <stdlib.h>

int BPU_mathInitCtx(BPU_T_Math_Ctx **ctx, const BPU_T_GF2_16x g, const BPU_T_GF2_16x mod) {
        BPU_T_GF2_16x b = 1;
        int i = 0;
        BPU_T_Math_Ctx *math_ctx;

        *ctx = (BPU_T_Math_Ctx *) calloc(1, sizeof(BPU_T_Math_Ctx));
        if (!*ctx) {
                BPU_printError("Can not malloc BPU_T_Math_Ctx");

                return -1;
        }
        math_ctx = *ctx;
        // get group ord, number of elements
        BPU_T_GF2_16x ord = ((1 << BPU_gf2xGetDeg(mod)) - 1);

        // alocate memory for tables
        math_ctx->mod = mod;
        math_ctx->mod_deg = BPU_gf2xGetDeg(mod);
        math_ctx->log_table = (BPU_T_GF2_16x*) malloc(sizeof(BPU_T_GF2_16x) * (ord + 1));
        math_ctx->exp_table = (BPU_T_GF2_16x*) malloc(sizeof(BPU_T_GF2_16x) * (ord + 1));

        // set ord
        math_ctx->ord = ord;

        do {
                math_ctx->exp_table[i] = b;
                math_ctx->log_table[b] = i;    

                b = BPU_gf2xMulMod(b, g, mod);
                i++;
        } while (b != 1);

        math_ctx->exp_table[ord] = 0;
        math_ctx->log_table[0] = ord;

        if (i != ord) {
                BPU_printError("element 0x%x is not generator", g);

                return 1;
        }
        return 0;
}

void BPU_mathFreeCtx(BPU_T_Math_Ctx **ctx) {
        if (!*ctx) {
                return;
        }
        if ((*ctx)->exp_table) {
                free((*ctx)->exp_table);
        }
        if ((*ctx)->log_table) {
                free((*ctx)->log_table);
        }
        free(*ctx);
        *ctx = NULL;
}