Java multiplication of same number returns different output in Python

Question

I am porting some Java code to Python, but for some reason, the results differ.

Java

int vi = 3997125 * 3997125;

Output: -270075495

Python

vi = 3997125 * 3997125

Output: 15977008265625

How would I accomplish the same output Java returns in Python?

In Java, an int is signed so that anything above 2^31 will be treated as a negative number. So if the output is > 2^31 then do 2^31 - (value) instead. — AlBlue
– AlBlue, Commented Dec 15, 2020 at 13:39

Mureinik · Accepted Answer · 2020-12-15 13:27:58Z

3

The Java snippet overflows. To avoid this, you could use longs:

long vi = 3997125L * 3997125L;

answered Dec 15, 2020 at 13:27

Mureinik

316k54 gold badges401 silver badges405 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Michael Szczesny · Accepted Answer · 2020-12-15 14:02:59Z

1

To simulate the conversion of a python integer to 32bit integer value with overflow

def bit32(value):
    shift =  1 << 32
    return value % shift - shift if value.bit_length() >= 32 else value
bit32(3997125*3997125)

Out:

-270075495

answered Dec 15, 2020 at 13:46

Michael Szczesny

5,0465 gold badges20 silver badges36 bronze badges

Updated my answer to work with integers without overflow.

Dev-vruper · Accepted Answer · 2020-12-15 13:34:06Z

1

The range of a variable declared as type int is -2,147,483,648 to 2,147,483,647 .

So when you do

3997125 * 3997125 = 15,977,008,265,625

which is out of range for a int type .

As suggested you can change the type to long .

answered Dec 15, 2020 at 13:34

Dev-vruper

4303 silver badges15 bronze badges