C#•9mo ago

✅ Random help

How do I get a random ulong out of Random.Next()? Random.NextInt64() seems to actually only give a random 63-bit number

ero•3/27/25, 9:45 AM

Cast it...?

ElectricTortoiseOP•3/27/25, 9:47 AM

i meant how do i get out a fully random 64 bit number

ElectricTortoiseOP•3/27/25, 9:47 AM

i can obviously cast it

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ElectricTortoiseOP•3/27/25, 9:48 AM

and then cast that to ulong?

ero•3/27/25, 9:48 AM

No?

ero•3/27/25, 9:48 AM

You'd need long.MinValue as the min

ero•3/27/25, 9:48 AM

The 64th bit is the sign

ElectricTortoiseOP•3/27/25, 9:48 AM

ahhh okok

ElectricTortoiseOP•3/27/25, 9:49 AM

i think i can do that

Eero The 64th bit is the sign

ElectricTortoiseOP•3/27/25, 9:49 AM

i can cast that to ulong right

ElectricTortoiseOP•3/27/25, 9:49 AM

this would work right

canton7•3/27/25, 9:51 AM

Yeah, that should work. (I'd use and )

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ElectricTortoiseOP•3/27/25, 9:52 AM

that's why i have the type cast there

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ElectricTortoiseOP•3/27/25, 9:52 AM

...then what is that point

ElectricTortoiseOP•3/27/25, 9:52 AM

that would turn -1 into 1

ElectricTortoiseOP•3/27/25, 9:52 AM

which leaves me with the same 63 bits worth of numbers

ElectricTortoiseOP•3/27/25, 9:52 AM

well then what does Math.Abs do

Kringe•3/27/25, 9:53 AM

NextInt64 return a non-negative long
https://learn.microsoft.com/en-us/dotnet/api/system.random.nextint64?view=net-9.0

Random.NextInt64 Method (System)

Returns a non-negative random integer.

ero•3/27/25, 9:53 AM

Too slow

KKringe NextInt64 return a non-negative long https://learn.microsoft.com/en-us/dotnet/ap...

ElectricTortoiseOP•3/27/25, 9:53 AM

there is an override

ero•3/27/25, 9:53 AM

*overload

KKringe NextInt64 return a non-negative long https://learn.microsoft.com/en-us/dotnet/ap...

ElectricTortoiseOP•3/27/25, 9:53 AM

this will take any int64, inclusive of negative ones

ero•3/27/25, 9:53 AM

I'd possibly wrap the cast in

Eero *overload

ElectricTortoiseOP•3/27/25, 9:53 AM

ah yea

Eero I'd possibly wrap the cast in `unchecked`

ElectricTortoiseOP•3/27/25, 9:55 AM

ooo ok

Eero I'd possibly wrap the cast in `unchecked`

ElectricTortoiseOP•3/27/25, 9:57 AM

it seems to be working without that tho

ElectricTortoiseOP•3/27/25, 9:58 AM

see

ElectricTortoiseOP•3/27/25, 9:58 AM

ok that's settled

EElectricTortoise it seems to be working without that tho

canton7•3/27/25, 10:00 AM

It will throw if you're in a

checked

checked

context, either because someone wrapped your method in

checked

checked

, or if the assembly was compiled with checked arithmetic

ElectricTortoiseOP•3/27/25, 10:01 AM

ElectricTortoiseOP•3/27/25, 10:02 AM

so slap unchecked on it gotchu

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ElectricTortoiseOP•3/27/25, 10:03 AM

yes

canton7•3/27/25, 10:03 AM

Yeah, it's one of those things that normally doesn't matter, but is good practice just for the odd case where it does matter for some reason

canton7•3/27/25, 10:04 AM

... Why?

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ElectricTortoiseOP•3/27/25, 10:04 AM

i need the number that comes out to be fixed

ElectricTortoiseOP•3/27/25, 10:04 AM

i seeded the random

canton7•3/27/25, 10:04 AM

(That also doesn't have a method for Int64's, FWIW)

ElectricTortoiseOP•3/27/25, 10:04 AM

it's ok the Random.NextInt64() works

ElectricTortoiseOP•3/27/25, 10:04 AM

just gotta tweak it a lil

canton7•3/27/25, 10:08 AM

I don't understand how makes it any easier to generate a random ulong ><

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canton7•3/27/25, 10:54 AM

I don't know how you determined that he needed a cryptographically secure random number from that discussion

Anton•3/27/25, 2:09 PM

use the overload, then reinterpret cast to ulong with

Anton•3/27/25, 2:10 PM

@ElectricTortoise

AAnton use the `Span<byte>` overload, then reinterpret cast to ulong with `Unsafe.As`

ElectricTortoiseOP•3/27/25, 2:11 PM

it's ok i have an easier solution already

AAnton use the `Span<byte>` overload, then reinterpret cast to ulong with `Unsafe.As`

Evyr•3/27/25, 4:58 PM

why not just ?

canton7•3/27/25, 4:59 PM

Why use Unsafe when you can just use a normal cast?

Evyr•3/27/25, 4:59 PM

fair

EEvyr why not just `Unsafe.BitCast<long, ulong>` ?

Anton•3/27/25, 7:36 PM

it's been established that it's positive, it's missing a bit of information

Anton•3/27/25, 7:37 PM

and the span overload is more flexible, if you know what you're doing

Anton•3/27/25, 7:38 PM

like if you're going to need 100 numbers, you can a buffer for all of them and generate them all at once