The bcmod function is deactivated and I won’t be able to activate this because its not my own server.
For a reason I need to calculate an integer with a length of atleast 24 with modulo 97. Integer cant be that long, thats why it can’t work…
I already tried it with simple operator “%” and the “fcmod” lib but this returns me completely wrong numbers.
Does someone know if I can solve this by my own without any other libraries or do I really need “bcmod”?
This would be the code as example:
123456789101112131415171%97
The real answer would be 96
but it returns me -94
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Answer
If you’ve got a number that is too big you can divide the problem into several steps with smaller numbers. An example:
Suppose we do this in steps of 3 digits. So, 1550 % 16
is the same as first doing 155 % 16
, which is 11
. After this first step we combine the result with what was left of the whole number. That is: 11
and 0
which gives 110
. We are now left with only 3 digits, so we do 110 % 16
which is 14
. So the result is 14
.
We can implement this in a function, I use 8 digits at once, because it is quicker:
function modulo($value, $modulo) { while ((strlen($value) > strlen($modulo)) || (intval($value) >= $modulo)) { $head = substr($value, 0, 8); $tail = substr($value, 8); $value = ($head % $modulo) . $tail; } return $value; }
Now if we do:
$value = "123456789101112131415171"; $modulo = 97; echo modulo($value, $modulo);
We get 96
. Note how the big integer is a string, otherwise it won’t work. There are a lot of implicit type conversions going on in this function.
See: PHP Sandbox.
A shorter version is possible, but is functionally the same:
function modulo($value, $modulo) { while ((strlen($value) > strlen($modulo)) || (intval($value) >= $modulo)) { $value = (substr($value, 0, 8) % $modulo) . substr($value, 8); } return $value; }
See: PHP Sandbox.