mohapatra_matrix_multiplication transformed to ISO C

mohapatra_matrix_multiplication.h

/*
  made 2021 by dbj@dbj.org
  
  https://godbolt.org/z/PjovPPoxf
*/
#include <assert.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#define FOR(C, R) for (unsigned C = 0; C < R; ++C)
/*
https://raw.githubusercontent.com/ShrohanMohapatra/matrix_multiply_quadratic/master/matrix_multiply_test.py
Transformation to standard C (c) 2021 by dbj@dbj.org 
 */
enum { N = 2 };

static void mohapatra(double A[N][N], double B[N][N], double E[N][N]) {
  double maxi = 0;
  FOR(i, N)
  FOR(j, N) {
    if (maxi < A[i][j]) maxi = A[i][j];
    if (maxi < B[i][j]) maxi = B[i][j];
  }
  int M = (int)(log10(maxi)) + 1;
  int P = (int)(log10((pow(10, (2 * M)) - 1) * N)) + 1;

  double C[N] = {0}, D[N] = {0};

  FOR(i, N) {
    double sum_1 = 0;
    FOR(j, N) sum_1 = sum_1 * (pow(10, P)) + A[i][j];
    C[i] = sum_1;  
  }
  FOR(j, N) {
    double sum_1 = 0;
    FOR(i, N) {
      sum_1 = sum_1 * (pow(10, P)) + B[N - 1 - i][j];
    }
      D[j] = sum_1;
  }

  FOR(i, N) {
    FOR(j, N) {
      E[i][j] = (int)(C[i] * D[j] / (pow(10, (P * (N - 1))))) % (int)(pow(10, P));
    }
  }
} // mohapatra

static void printmat(double mx[N][N]) {
  FOR(j, N) {
    FOR(k, N) { printf(" %4.2f ", mx[j][k]); }
    printf("\n");
  }
}

int main(void) {
  double a[2][2] = {{1, 2}, {3, 4}};
  double b[2][2] = {{5, 6}, {7, 8}};

printf(
"\nThe constelation"
"\nof matrices, to check the correctness:"
"\n"
"\n     | 1 2 |      | 5 6 |       | 19 22 |"
"\n     |     |  x   |     |  =    |       |"
"\n     | 3 4 |      | 7 8 |       | 43 50 |"
"\n" ) ;

  {
  double r[2][2] = {{0, 0}, {0, 0}};
  mohapatra(a, b, r);
  printf("\nAfter R = mohapatra(A,B) the result is:\n\n");
  printmat(r);
  }

printf(
"\nAlgorithm:"
"\n"
"\nhttps://raw.githubusercontent.com/ShrohanMohapatra/matrix_multiply_quadratic/master/matrix_multiply_test.py"
"\nBSD 3-Clause License"
"\nCopyright (c) 2019, ShrohanMohapatra"
"\nAll rights reserved."
"\n"
"\nTransformation to C (c) 2021 by dbj@dbj.org"
);

  return 42;
}