Can't calculate value in Python

Question

I am trying to calculate value of this expression:

int((1770246808796936040 * 1103515245 + 12345 / 65536) % 32768)

And it gives 0. Without int cast, it is 0 too.

Does anyone know why it so? Are these numbers too big for Python? Is any way to handle the issue? Appreciate any help.

I guess the issue is resolved, mark any of the answers as accepted to close it. — Jarvis, Dec 26 '20 at 14:28
What do you think the answer should be, and why? It looks like one step of an [LCG](https://en.wikipedia.org/wiki/Linear_congruential_generator), in particular see the 4th line of [this table](https://en.wikipedia.org/wiki/Linear_congruential_generator#Parameters_in_common_use), but you have misunderstood the order of operations and incorrectly parenthesized it. In python a correct expression would be `((1770246808796936040 * 1103515245 + 12345) // 65536) % 32768` — President James K. Polk, Dec 26 '20 at 15:56

Jarvis · Answer 1 · 2020-12-26T12:14:24.257

The number calculated from the expression

1770246808796936040 * 1103515245 + 12345 / 65536

is divisible by 32768, that's why you get 0.

To give you an idea of Python's capacity to handle huge numbers, you can see this:

>>> 10**1000

10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

score 2 · Answer 2 · answered Dec 26 '20 at 12:08

2

The % operator gives the remainder of a division. Since

(1770246808796936040 * 1103515245 + 12345 / 65536)

is divisible by 32768, the result is 0. To obtain the quotient, you should use the operator / instead of %.

answered Dec 26 '20 at 12:08

aargun

126
4

score 1 · Answer 3 · answered Dec 26 '20 at 12:07

Because the numbers' combination is such that the result is 0. Increase or decrease any number by even 1 and you will see that it is not 0. For example see below. I changed 32768 to 32769.

print(int((1770246808796936040 * 1103515245 + 12345 / 65536) % 32769))

It gives.

Can't calculate value in Python

3 Answers3