bcdiv using very small float with scientific notation cause "Division by zero" error

Question

Using bcdiv, i can't divide with small float using scientific notation :

Working code :

bcscale(30);
$a = '1' ;
$b = '0.00000001';
$result = bcdiv($a, $b);
var_dump($result);

Results in :

string(20) "100000000.0000000000"

Non-working code :

bcscale(30);
$a =  '1' ;
$b =  '1e-8';
$result = bcdiv($a, $b);
var_dump($result);

Results in :

Warning: bcdiv() [function.bcdiv]: Division by zero in C:\wamp\www\utilitaires\test_bcdiv.php on line XX NULL

How can i do this division properly, with the less precision loss ?

Vibrio

Are you sure, that the bc-functions support scientific notation? I can't hind any hint on that in the documentation. – Andry

@Andry it doesn't support that. But - you're right, that need to be clarified implicitly – Fann

Answer 1

That is because, actually, bcmath doesn't support scientific notation. It isn't mentioned in manuals, but as you can see, in it's implementation argument conversion is used, it's named php_str2num:

static void php_str2num(bc_num *num, char *str TSRMLS_DC)
{
    char *p;

    if (!(p = strchr(str, '.'))) {
        bc_str2num(num, str, 0 TSRMLS_CC);
        return;
    }

    bc_str2num(num, str, strlen(p+1) TSRMLS_CC);
}

and so bc_str2num:

bc_str2num (bc_num *num, char *str, int scale TSRMLS_DC)
{
  int digits, strscale;
  char *ptr, *nptr;
  char zero_int;

  /* Prepare num. */
  bc_free_num (num);

  /* Check for valid number and count digits. */
  ptr = str;
  digits = 0;
  strscale = 0;
  zero_int = FALSE;
  if ( (*ptr == '+') || (*ptr == '-'))  ptr++;  /* Sign */
  while (*ptr == '0') ptr++;            /* Skip leading zeros. */
  while (isdigit((int)*ptr)) ptr++, digits++;   /* digits */
  if (*ptr == '.') ptr++;           /* decimal point */
  while (isdigit((int)*ptr)) ptr++, strscale++; /* digits */
  if ((*ptr != '\0') || (digits+strscale == 0))
    {
      *num = bc_copy_num (BCG(_zero_));
      return;
    }

  /* Adjust numbers and allocate storage and initialize fields. */
  strscale = MIN(strscale, scale);
  if (digits == 0)
    {
      zero_int = TRUE;
      digits = 1;
    }
  *num = bc_new_num (digits, strscale);

  /* Build the whole number. */
  ptr = str;
  if (*ptr == '-')
    {
      (*num)->n_sign = MINUS;
      ptr++;
    }
  else
    {
      (*num)->n_sign = PLUS;
      if (*ptr == '+') ptr++;
    }
  while (*ptr == '0') ptr++;            /* Skip leading zeros. */
  nptr = (*num)->n_value;
  if (zero_int)
    {
      *nptr++ = 0;
      digits = 0;
    }
  for (;digits > 0; digits--)
    *nptr++ = CH_VAL(*ptr++);

  /* Build the fractional part. */
  if (strscale > 0)
    {
      ptr++;  /* skip the decimal point! */
      for (;strscale > 0; strscale--)
    *nptr++ = CH_VAL(*ptr++);
    }
}

-not hard to see that it will fail on scientific notation (well-commented). Perhaps documentation needs to be updated (to mention that implicitly).

Possible solution will be to convert your string to plain view before applying bcmath functions

Fann

Yes, thanks for confirming this point. I will code my own convert function exp float > full str. I can't have the result that i want using existing php function (like number_format or just type casting ...). If you have any brillant and simple idea ... Thanks again Eric – Vibrio

It's good question. I asked it here. I have solution for that, but sure community will propose better way – Fann