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#include <cstdlib>
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#include <cstring>
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#include <cmath>
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#include <cstdio>
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#include "stc_extract_c.h"
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int stc_extract(const u8 *vector, int vectorlength, u8 *message, int syndromelength, int matrixheight)
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{
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int i, j, k, index, index2, base, height;
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u8 *binmat[2];
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int *matrices, *widths;
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height = matrixheight;
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if(matrixheight > 31) {
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fprintf(stderr, "Submatrix height must not exceed 31.");
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return -1;
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}
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{
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double invalpha;
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int shorter, longer, worm;
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u32 *columns[2];
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matrices = (int *)malloc(syndromelength * sizeof(int));
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widths = (int *)malloc(syndromelength * sizeof(int));
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invalpha = (double)vectorlength / syndromelength;
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if(invalpha < 1) {
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fprintf(stderr, "The message cannot be longer than the cover object.\n");
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return -1;
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}
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shorter = (int)floor(invalpha);
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longer = (int)ceil(invalpha);
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if((columns[0] = getMatrix(shorter, matrixheight)) == NULL) {
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free(widths);
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free(matrices);
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return -1;
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}
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if((columns[1] = getMatrix(longer, matrixheight)) == NULL) {
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free(columns[0]);
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free(widths);
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free(matrices);
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return -1;
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}
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worm = 0;
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for(i = 0; i < syndromelength; i++) {
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if(worm + longer <= (i + 1) * invalpha + 0.5) {
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matrices[i] = 1;
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widths[i] = longer;
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worm += longer;
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} else {
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matrices[i] = 0;
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widths[i] = shorter;
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worm += shorter;
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}
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}
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binmat[0] = (u8*)malloc(shorter * matrixheight * sizeof(u8));
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binmat[1] = (u8*)malloc(longer * matrixheight * sizeof(u8));
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for(i = 0, index = 0; i < shorter; i++) {
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for(j = 0; j < matrixheight; j++, index++) {
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binmat[0][index] = (columns[0][i] & (1 << j)) ? 1 : 0;
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}
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}
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for(i = 0, index = 0; i < longer; i++) {
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for(j = 0; j < matrixheight; j++, index++) {
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binmat[1][index] = (columns[1][i] & (1 << j)) ? 1 : 0;
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}
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}
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free(columns[0]);
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free(columns[1]);
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}
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for(i = 0; i < syndromelength; i++) {
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message[i] = 0;
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}
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for(index = 0, index2 = 0; index2 < syndromelength; index2++) {
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for(k = 0, base = 0; k < widths[index2]; k++, index++, base += matrixheight) {
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if(vector[index]) {
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for(i = 0; i < height; i++) {
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message[index2 + i] ^= binmat[matrices[index2]][base + i];
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}
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}
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}
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if(syndromelength - index2 <= matrixheight)
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height--;
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}
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free(matrices);
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free(widths);
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free(binmat[0]);
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free(binmat[1]);
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return 0;
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}
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