Why does this function fail??

[ppowell]

if (!function_exists('convert_number_to_unit')) {

 function convert_number_to_unit($number, $unit) {
  if ((int)$number === 0 || !$unit) return $number;
  // RECURSION METHOD TO BREAK NUMBER DOWN 
  switch (strtoupper($unit)) {
   case 'TB' :			// TERABYTES
    return (double)number_format(convert_number_to_unit($number, 'mb') / 1000); 
    break;
   case 'MB' :			// MEGABYTES
    return (double)number_format(convert_number_to_unit($number, 'kb') / 1000);
    break;
   case 'KB' :			// KILOBYTES
    return (double)number_format($number / 1000);
    break;
  }
 }
}

echo convert_number_to_unit('1000000', 'mb'); // RETURNS "0" BUT SHOULD RETURN 1

I am at a loss! This function should perfectly work as it seems logically and mathematically accurate, but it always returns 0 no matter what value you put into the function. What on earth am I doing to cause such an impossibility?? Recursive numerical functions could never return 0 because it's impossible to achieve by division!

Help!

Thanx
Phil

[planetsim]

Perhaps try this

<?php

if (!function_exists('convert_number_to_unit')) 
{

 function convert_number_to_unit($number, $unit)
 {
     if ($number === 0 || !$unit) {  return $number; }
     // RECURSION METHOD TO BREAK NUMBER DOWN
     switch (strtoupper($unit)) 
     {
         case "TB":            // TERABYTES
            return number_format(convert_number_to_unit($number, 'mb') / 1024); 
         break;
         case "MB":            // MEGABYTES
            return number_format(convert_number_to_unit($number, 'kb') / 1024);
         break;
         case "KB":            // KILOBYTES
            return number_format($number / 1024);
         break;
     }
 }
}

echo convert_number_to_unit('1000000', 'mb'); // RETURNS "0" BUT SHOULD RETURN 1 

?>

I remember that it was 1024 kilobytes to a megabyte, 1024 megabytes to a gigabyte and so on.

[mrhappiness]

Your use of number_format converts 1000000 / 1000 to 1,000 (K😎

1,000 (K😎 is a string that is converted to a number by your next call to number-format (for M😎
The string 1,000 (K😎 gets evaluated to the number 1.
1 / 1000 = 0,001 (M😎 => 0

Try

function convert_number_to_unit($number, $unit, $first_call = true) {
	if ((int)$number === 0 || !$unit) return $number;

switch (strtoupper($unit)) {
	case 'TB' :     
			$result = convert_number_to_unit($number, 'MB', false) >> 10;
			break;
	case 'MB' :            // MEGABYTES
			$result = convert_number_to_unit($number, 'KB', false) >> 10;
			break;
	case 'KB' :            // KILOBYTES
			$result = $number >> 10;
			break;
}

if ($first_call)
	return number_format($result).' '.strtoupper($unit);
else
	return $result;

}

[drew010]

ummm is it just that im high or does the terminating condition look a little like it always returns a 0 number...
if ((int)$number === 0 || !$unit) return $number;
when is $unit ever !

and mr.h i like that right shift >>🙂

[mrhappiness]

drew010 wrote:

ummm is it just that im high or does the terminating condition look a little like it always returns a 0 number...
if ((int)$number === 0 || !$unit) return $number;
when is $unit ever !

the condition is satisfied if either $number evaluates to 0 or if $unit evaluates to false or if both "subconditions" are true ($number == 0 and $unit == false)

$unit is false if it's false, 0, '0' or empty

i like that right shift >>🙂

me to 😉

[drew010]

yes but the function cant be called with an empty argument, and its never called with unit anything but tb gb mb kb (at least that my eyes can see now hehe), so therefore it always terminates with $number being 0 and then returns the 0 itself.

[mrhappiness]

echo convert_number_to_unit('1000000', 'mb');

$number is not 0 and $unit is 'mb' which is not false.
why should the function return 0?

echo convert_number_to_unit('1000000', 0);

$unit evalutes to false 😉

[drew010]

echo convert_number_to_unit('1000000', 0);

i know thats possible but is there any point in the recursive body where it gets called like that?

and it returns 0 because of
if ((int)$number === 0 || !$unit) return $number;

it doesnt matter what $number has been, its 0 at that point, and when its 0 the bottom call on the recursive stack returns, 0.

[mrhappiness]

but if it's 0 and the function returns 0 to the caller (may it be the script or may it be the same function) - where's the problem?

[drew010]

iono, i guess im thinking the function is supposed to return some formatted number of some sort instead of just 0.
like the line
'1000000', 'mb')
i think its passed 1 million bytes and we want that expressed in megabyte?? i see the function always returning 0....

[mrhappiness]

did you test the function i posted?

[Weedpacket]

I reckon mrhappiness has got it: number_format(1000000/1000) is "1,000" and (double)"1,000" is 1; while number_format(1/1000) is "0" because there was no precision specified.

But recursion seems like a silly way of doing this anyway.

[grrosey]

Um... am I just missing the point here, or is someone missing the GB in there? I see TB, MB, KB, but no GB. Is it possible because you are missing a whole number place holder, that it is returning the incorrect information?

Just a thought, I haven't done programming in so long that it is like falling down on a bike over and over, hehehe 😃 .

[planetsim]

It just doesnt get processed the swtich statement gets what size its suppose to be either KB, MB or TB as the unit and since GB isnt specified I take it its not suppose to be done, also there is no default case incase $unit is true and $number is 0 nothing will be returned.

[ppowell]

Weedpacket wrote:

I reckon mrhappiness has got it: number_format(1000000/1000) is "1,000" and (double)"1,000" is 1; while number_format(1/1000) is "0" because there was no precision specified.

But recursion seems like a silly way of doing this anyway.

Why is this silly? It's the most efficient way of dealing with this, tell me a better way, considering I wrote it!

Phil

[ppowell]

To MrHappiness:

Please explain what the heck ">> 10" is. You completely lost me.

Thanx
Phil

[mrhappiness]

switch ($unit) {
  case 'KB': return number_format($number / 1024);
  case 'MB': return number_format($number / 1048576);
  case 'GB': return number_format($number / 1073741824);
}

like that?

The ">> 10" shifts the bitwise representation of $number by 10 places to the right => $number = $number >> 10 equals $number = $number / 1024 as 2¹⁰ = 1024

just shifting to the right ought to be faster that having the computer actually calculate the result of a division

disadvantage of shifting: you completly ignore the fraction

for example:
656463 (decimal) is 10100000010001001111 (binary)

656463 / 1024 = 641,0771484375

656463 >> 10 = 1010000001 (binary) = 641