#include <string.h>
#include <stdint.h>
#include <stdio.h>
#include "erasure_code.h"

#define MAX_CHECK 63 /* Size is limited by using uint64_t to represent subsets */
#define M_MAX     0x20
#define K_MAX     0x10
#define ROWS      M_MAX
#define COLS      K_MAX

static inline uint64_t
min(const uint64_t a, const uint64_t b)
{
        if (a <= b)
                return a;
        else
                return b;
}

void
gen_sub_matrix(unsigned char *out_matrix, const uint64_t dim, unsigned char *in_matrix,
               const uint64_t rows, const uint64_t cols, const uint64_t row_indicator,
               const uint64_t col_indicator)
{
        uint64_t i, j, r, s;

        for (i = 0, r = 0; i < rows; i++) {
                if (!(row_indicator & ((uint64_t) 1 << i)))
                        continue;

                for (j = 0, s = 0; j < cols; j++) {
                        if (!(col_indicator & ((uint64_t) 1 << j)))
                                continue;
                        out_matrix[dim * r + s] = in_matrix[cols * i + j];
                        s++;
                }
                r++;
        }
}

/* Gosper's Hack */
uint64_t
next_subset(uint64_t *subset, uint64_t element_count, uint64_t subsize)
{
        uint64_t tmp1 = *subset & -*subset;
        uint64_t tmp2 = *subset + tmp1;
        *subset = (((*subset ^ tmp2) >> 2) / tmp1) | tmp2;
        if (*subset & (((uint64_t) 1 << element_count))) {
                /* Overflow on last subset */
                *subset = ((uint64_t) 1 << subsize) - 1;
                return 1;
        }

        return 0;
}

int
are_submatrices_singular(unsigned char *vmatrix, const uint64_t rows, const uint64_t cols)
{
        unsigned char matrix[COLS * COLS];
        unsigned char invert_matrix[COLS * COLS];
        uint64_t subsize;

        /* Check all square subsize x subsize submatrices of the rows x cols
         * vmatrix for singularity*/
        for (subsize = 1; subsize <= min(rows, cols); subsize++) {
                const uint64_t subset_init = (1ULL << subsize) - 1ULL;
                uint64_t col_indicator = subset_init;
                do {
                        uint64_t row_indicator = subset_init;
                        do {
                                gen_sub_matrix(matrix, subsize, vmatrix, rows, cols, row_indicator,
                                               col_indicator);
                                if (gf_invert_matrix(matrix, invert_matrix, (int) subsize))
                                        return 1;

                        } while (next_subset(&row_indicator, rows, subsize) == 0);
                } while (next_subset(&col_indicator, cols, subsize) == 0);
        }

        return 0;
}

int
main(int argc, char **argv)
{
        unsigned char vmatrix[(ROWS + COLS) * COLS];
        uint64_t rows, cols;

        if (K_MAX > MAX_CHECK) {
                printf("K_MAX too large for this test\n");
                return 0;
        }
        if (M_MAX > MAX_CHECK) {
                printf("M_MAX too large for this test\n");
                return 0;
        }
        if (M_MAX < K_MAX) {
                printf("M_MAX must be smaller than K_MAX");
                return 0;
        }

        printf("Checking gen_rs_matrix for k <= %d and m <= %d.\n", K_MAX, M_MAX);
        printf("gen_rs_matrix creates erasure codes for:\n");

        for (cols = 1; cols <= K_MAX; cols++) {
                for (rows = 1; rows <= M_MAX - cols; rows++) {
                        gf_gen_rs_matrix(vmatrix, rows + cols, cols);

                        /* Verify the Vandermonde portion of vmatrix contains no
                         * singular submatrix */
                        if (are_submatrices_singular(&vmatrix[cols * cols], rows, cols))
                                break;
                }
                printf("   k = %2u, m <= %2u \n", (unsigned) cols, (unsigned) (rows + cols - 1));
        }
        return 0;
}