Go: convert big.Int to regular integer (int, int32, int64)

Question

I assumed this would be a simple issue with abundant answers on the Internet. But that does not appear to be the case.

I need to convert a Go big.Int into a regular integer (e.g., int, int32, or int64). But there appears to be no straightforward way to do this.

I've tried int(bigVal), int32(bigVal), and int64(bigVal), but they give the error cannot convert bigVal(variable of type big.Int) to type x (where x is either int, int32 or int64).

I'm finding myself frustrated over how Go makes handling big numbers so complicated (in contrast to the relative ease of, say, C#/.NET's System.Numerics.BigInteger). How do I accomplish this, something that should a trivially easy task?

Just asking: You are aware of the implications, right? Bigint Range is way larger than e.g. int range. — Erhard Dinhobl
– Erhard Dinhobl, Commented Feb 11, 2024 at 20:00
@ErhardDinhobl yes I am aware of the implications, but there is no risk of overflow because I am using Mod on the number before I try to convert it. — Cade Bryant
– Cade Bryant, Commented Feb 11, 2024 at 20:02
Have you tried theBigInt.Int()? I remember slt. I am not that familiar with Go but i once read the docs. — Erhard Dinhobl
– Erhard Dinhobl, Commented Feb 11, 2024 at 20:04
Would consulting the documentation of math/big.Int be an option? — Volker
– Volker, Commented Feb 11, 2024 at 20:11

Cade Bryant · Accepted Answer · 2024-02-11 21:39:24Z

0

@Eldar was correct. Thank you! big.Int has an instance-level method called Int64() that returns the 64-bit integer representation of the value (or undefined if it cannot be represented as such).

I merely needed to wrap it wothint32() to get the desired result:

int32(bigVal.Int64())

answered Feb 11, 2024 at 21:39

Cade Bryant

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Deltics Over a year ago

Int64() doesn't "return undefined" in the sense of returning a value that identifies that the value is undefined. "undefined" in this context is not the same as, say, "NaN", in the context of a float, for example. Rather, the return value being "undefined" is a warning that there is no contract or specification for what is returned in that case; your code should not rely on that the current implementation happens to return in such cases (i.e. always the lowest 64 bits of the value). It could change in the future, e.g. to return 0 or -1 etc for some reason (e.g. efficiency).

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