Question

Please provide some code for converting char[] array of decimal values to bytes array for big integer value in c.

How can I convert this below code for big array of decimal value, such as I get the result as array of long bytes?

static int dec2bin (char inbuf[], int num_convert)
{
  char ctemp;
  int result, power;

  num_convert--; /* index of LS char to convert */
  result = 0;
  power = 1;
  while (num_convert >= 0)
  {
    ctemp = inbuf[num_convert--]; /* working digit */
    if (isdigit(ctemp))
    {
      result += ((ctemp-'0') * power);
      power *= 10;
    }
    else
      return(0); /* error: non-numeric digit detected */
  }
  return (result);
}

No it is not just long value , it is really a biginteger value , can anyone give a simple dec to byte(binary conversion logic , i will replace the int with my bigint implementations and bigint operators(add, mult) etc.,

Samuel is correct!

Thanks in advance.

For Example i can replace the above as below

static int dec2bin (char inbuf[], bigint num_convert) 
{ 
  char ctemp; 
  bigint result, power; 

  num_convert--; /* index of LS char to convert */ 
  result = 0; 
  power = 1; 
  while (num_convert >= 0) 
  { 
    ctemp = inbuf[num_convert--]; /* working digit */ 
    if (isdigit(ctemp)) 
    { 
      result = bi_add(result ,(bi_mult((ctemp-'0'), power)); 
      power = bi_mult(power , 10); 
    } 
    else 
      return(0); /* error: non-numeric digit detected */ 
  } 
  return (result); 
} 

something like this will work ?

Answer 1

It sounds like you are looking for a solution where you do the low level arithmetic yourself.

Have you considered using an existing bignum package such as the GNU Multi Precision Arithmetic library? It’s pretty easy to convert your existing code once you have that. For example, this code:

result += ((ctemp-'0') * power);
power *= 10;

becomes:

mpz_t tmp;
mpz_init(tmp);
mpz_mul_ui(tmp, power, ctemp - '0');
mpz_add(result, result, tmp);
mpz_clear(tmp);

mpz_mul_ui(power, power, 10);