Szathmáry László honlapja @ DEIK

bigints is a 3rd-party library for working with arbitrary precision integers.

$ nimble install bigints

Links:

on GitHub: https://github.com/nim-lang/bigints
documentation: https://nim-lang.github.io/bigints/

bigints provides a BigInt type and related operations with standard Nim syntax:

creation of BigInt from all standard integer types (initBigInt)
comparisons (<, ≤, ==)
addition, negation and subtraction (+, -, += -=)
multiplication (*, *=)
bit shifts (shr, shl)
bitwise not, and, or and xor (behave as if negative numbers were represented in 2's complement)
integer division and modulo operation (div, mod)
conversion of BigInt from/to strings supporting bases from 2 to 36 (initBigInt, $)
iteration utilities (inc, dec, countdown, countup, .., ..<)

There's also a pow() function:

func pow(x: BigInt, y: Natural): BigInt

The Natural type means that y cannot be negative.

import bigints

let
a: BigInt = initBigInt(0) # 0 as BigInt
b = initBigInt(2) # 2 as BigInt
c = 5.initBigInt # 5 as BigInt (alternative syntax)
d = "645347534".initBigInt # create a BigInt from a string

Example

How much is 2²⁵⁶?

import bigints

let result = pow(2.initBigInt, 256)

echo result

let s: string = $result

echo s

Output:

115792089237316195423570985008687907853269984665640564039457584007913129639936
115792089237316195423570985008687907853269984665640564039457584007913129639936

As you can see, a BigInt can be converted to a string with the `$` operator.

Notes

I know that in D Lang, BigInt performance is optimized for numbers below ~1000 decimal digits. I'm not sure but I think it's similar in Nim too.
I tried the pow() function to produce a really huge number and it was very slow. Interestingly, for very large numbers, Python performs much better.
For very large numbers, consider using the GMP library instead. There are Nim bindings to it but I haven't tried them yet.