Description:
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The modulus operator % returns wrong results if the number gets large. In a program used to calculate primes, it will find that large numbers, ending in 5, are prime. The following are calculations using % on such a large number, note that all numbers used in the MOD calculation are whole integers (and should not suffer rounding by MOD):

MOD: 53253252355 % 3=1 
DIV: 53253252355 / 3=17751084118.333332061767578125

MOD: 53253252355 % 4=3 
DIV: 53253252355 / 4=13313313088.75

MOD: 53253252355 % 5=2 
DIV: 53253252355 / 5=10650650471

Obviously, any number ending in 5 cannot be prime, since it will always be divisible by 5. The MOD result on 5 is therefore wrong, as the division proves.

Reproduce code:
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$i=53253252355;
ini_set("precision",35);

for ($m=2; $m<=$i; $m++){
 echo "MOD: $i % $m=". $i % $m ;
 echo "DIV: $i / $m=". $i/$m ."<Br>";     
 }

Expected result:
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I would expect to see 

MOD: 53253252355 % 3=1 
DIV: 53253252355 / 3=17751084118.333332061767578125
MOD: 53253252355 % 4=3 
DIV: 53253252355 / 4=13313313088.75
MOD: 53253252355 % 5=0 
DIV: 53253252355 / 5=10650650471

Actual result:
--------------
However, this is produced: ([THE ERROR] added for your convenience)

MOD: 53253252355 % 3=1 
DIV: 53253252355 / 3=17751084118.333332061767578125
MOD: 53253252355 % 4=3 
DIV: 53253252355 / 4=13313313088.75
MOD: 53253252355 % 5=2 [THE ERROR]
DIV: 53253252355 / 5=10650650471