mod2^n by sum

#include <stdio.h>
#include <math.h>

#define MAX_DIG 32 //maximum digits in any base

typedef struct {
  int x; //number in base10
  int N; //number of digits
  int b; //base for d
  int d[MAX_DIG]; //digits of a number
  int r; //remainder, d mod(b-1)
} numb;

void sum_d(numb* n) //=n.d mod(n.b-1)
{
  n->r=0;

  for (int i=0; i<n->N; i++) {
    n->r+=n->d[i];

    if(n->r>=n->b) {
      n->r-=(n->b-1);
    }
  }

  if (n->r==n->b-1) n->r=0;
}

void to_base(int b, numb* n) //b=2^i, where i=1,2,3,...
{
  //TODO:convert to baseb more easily
}

void gen_numb(int b, int Nd, int x, numb* n) //b=2^i, where i=1,2,3,4,..
{
  n->N=Nd; //number of digits in base b
  n->b=b;
  int Nb=log2(b); //number of bits per digit in base b
  int i = 0;
  int j = 0;

  for (i=0; i < Nd; i++) {
    n->d[i]=(x & ((b-1) << j)) >> j;

    j+=Nb;
  }

  n->x=x;

  sum_d(n);
}

int main(void)
{
    #define N_VALS 3
    #define N_BASE 5

    const int bx[N_BASE] = {64,32,16,8,4}; //base of x
    const int x[N_VALS] = {791,135727,478};
    const int Nd[N_VALS][N_BASE] = {  //Nd for x[i] in all bases
        {2,2,3,4,5},
        {3,4,5,6,9},
        {2,2,3,3,5}
    }; //number of digits in x

    numb n;

    for(int i=0; i<N_VALS; i++) {
        for(int j=0; j<N_BASE; j++) {
            gen_numb(bx[j],Nd[i][j],x[i],&n);

            printf("x=%u,b=%u,r=%u",x[i],bx[j],n.r);

            if (n.r == x[i]%(bx[j]-1)) printf("   ...OK\r\n");
            else printf("   ...FAIL, r=%u\r\n",x[i]%(bx[j]-1));
        }
    }

    return 0;
}