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64-bit bank balances ‘ought to be enough for anybody’?

tigerbeetle.com

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Re: 64-bit bank balances ‘ought to be enough for anybody’?

#271

Post by leosarev »

vidarh wrote: post #256
pixl97 wrote: post #247

Earlier quoted context omitted.

I think for most large businesses there are pretty considerable error bars here. If you say you owe 1,000,000 a year in VAT and the government says you owe 1,010,000 it's cheaper to pay the difference then dig into why it's off.

If you report 1,000,000 and certify that it's the right number, and the government audits you and find you should have paid 1,010,000, then depending on jurisdiction you might be entirely ok, or you might find you're not going to be paying just the difference, and interest, but also a fine, and bearing the cost of additional audits going forward, and that your finance director will not appreciate having to address qu…

It's strange. In Russia, small error in VAT will get you a letter from tax service "pay us a small error voluntarily, or we will schedule an inspection". Letter will be automatically generated by ASK-NDS system (translated as Auto Check Vat).

Re: 64-bit bank balances ‘ought to be enough for anybody’?

#273

Post by HWR_14 »

amalcon wrote: post #170
pjc50 wrote: post #155

Earlier quoted context omitted.

I did join somewhere that could do it correctly, because they had some very long-running POS software. It could even do things like "split bill three ways" correctly allocating both the spare penny from the division and the tax calculation, such that you could add the bills back together again and get the same numbers as the split bill. Using a "money" class that stores things as integer pennies gets you a long way t…

Integer cents is fantastic for POS software and similar things that deal with at most a few thousand dollars at a time. The place where it starts to fail is when the absolute numbers get really large, not really small. Think "United States Federal Reserve" or "UBS". Then remember that some of these institutions need to deal with accounts denominated in Zimbabwean dollars.

The current US national debt represented in integer cents requires 52 bits. It can trivially increase 4,000x before we need to worry about 64-bit balances.

Re: 64-bit bank balances ‘ought to be enough for anybody’?

#274

Post by hot_gril »

> For the same reason, digital currencies are another use case for 128-bit balances, where again, the smallest quantity of money can be represented on the order of micro-cents (10-6)… or even smaller.

To give a concrete example, Ethereum has a lot of precision (1 ether = 10^18 wei), and there are like 120M ether, so that's more than 64 bits just to represent the supply.

Idk though, is this a real concern with traditional finance? Zimbabwe had their huge bills, but I assume the small ones were unused. Just like you round US cents, you could probably round their currency at some cutoff. If you were processing Ether outside the blockchain like just some other currency, you'd probably round somewhere too. If you look at Stripe's API for example, they do everything with fixed-size (JSON's 53-bit) integers defined as cents or whatever.

Re: 64-bit bank balances ‘ought to be enough for anybody’?

#275

Post by tombert »

dahfizz wrote: post #11
Etheryte wrote: post #3

Perhaps I'm the odd one out here, but most financial systems I've had the chance to work with don't actually use numeric types to store values, they use strings or other comparable types. Numeric values are passed to all outside interfaces, but the internal states are written in a way where no bit level issues peddle with the values. I'm wondering what the experience of the wider audience here is?

Sounds slow as hell, what kind of financial systems have you worked with? I write trading software, and pretty much everyone uses integers with implied decimal place, similar to TFA. How do you know you convert your internal string to a float/int correctly? You have to deal with the numeric types eventually

I've never written any trading software, but out of curiosity, have you done any tests comparing something like a GMP arbitrary-precision number vs a raw integer type.

Obviously the raw integer (64 bit or 128 bit) will go faster since it would have CPU-level assistance, but I'm curious to what that actually ends up being in practice, especially at the scale of trading. Is it 10% faster? 10X faster? Somewhere in between?

Re: 64-bit bank balances ‘ought to be enough for anybody’?

#276

Post by JeremyNT »

hot_gril wrote: post #274

> For the same reason, digital currencies are another use case for 128-bit balances, where again, the smallest quantity of money can be represented on the order of micro-cents (10-6)… or even smaller. To give a concrete example, Ethereum has a lot of precision (1 ether = 10^18 wei), and there are like 120M ether, so that's more than 64 bits just to represent the supply. Idk though, is this a real concern with traditi…

> Idk though, is this a real concern with traditional finance? Zimbabwe had their huge bills, but I assume the small ones were unused. Just like you round US cents, you could probably round their currency at some cutoff. If you were processing Ether outside the blockchain, you'd probably round somewhere too.

Yeah... I started reading this article and was waiting for the crypto angle, because in normal finance I don't see how it could plausibly matter (disclaimer: not my domain).

The only reason I could imagine needing to track this level of precision on fractional units of currency was the sort of financial trickery that is enabled by cryptocurrencies.

Re: 64-bit bank balances ‘ought to be enough for anybody’?

#277

Post by Shish2k »

jjgreen wrote: post #220
ilyt wrote: post #207

Earlier quoted context omitted.

> 0.3-0.2-0.1 -2.7755575615628914e-17 And now you overdrafted

Do it a million trillion times and we're talking cents overdrafted (almost)

If a rounding error put me a million-trillionth of a cent into my overdraft, I’m pretty sure my bank would still activate that $20/mo overdraft fee :P

Re: 64-bit bank balances ‘ought to be enough for anybody’?

#278

Post by brewdad »

david422 wrote: post #162
forinti wrote: post #43

Earlier quoted context omitted.

I have a personal anecdote on this subject. A long time ago I worked at a bank and I had to calculate a large number of accounts regarding agricultural loans. These were state sponsored loans. When I finished my task (this was a Java job), I found that sometimes the results were off by $0.01. So I asked my boss how I should do the rounding, to which he replied that an error of up to $1 was acceptable. If I recall cor…

Whenever I input my tax data on forms, it always rounded to the nearest dollar. It was strange that accuracy didn't seem to be a big priority.

I imagine over millions of returns it probably evens out. Also, for the majority of taxpayers in the US, the tax table does things like:

AGI is 40,001 to 40,025 then your tax is X dollars.

Being accurate to the penny isn't worth the trouble.

Re: 64-bit bank balances ‘ought to be enough for anybody’?

#279

Post by Dylan16807 »

Merad wrote: post #248
vidarh wrote: post #184

Earlier quoted context omitted.

A shocking number of people (edit: who implement billing related software) are unaware of how many decimal points of accuracy their local tax code requires to calculate vat or sales tax correctly. And those things are often specified in terms of arithmetic correctness. I had our CFO stand behind me while I talked him through every step of our VAT calculations once, because he was legally responsible if I made us roun…

A shocking number of people who work with software that handles money are just winging it. I worked on a project once that handled payment processing functionality for other products at the company (it was a B2B SaaS where clients could take payments through our software). We also handled payments related billing, since the clients would owe fees to us and to our payments gateway for their transactions. The payments…

Why was it listed separately at all?

If the month's charges were 406.783228 and I get a bill for 406.79 then that seems perfectly good.

If I get a bill that says 406.78, plus a separate 0.01, that's weird.

Re: 64-bit bank balances ‘ought to be enough for anybody’?

#280

Post by jorangreef »

walnutclosefarm wrote: post #258

I'd like a report back from TigerBeetle on how many applications they actually support where the high order 64 bits are nonzero. I would note that the entire US GDP is less than 10^15 cents, and that 2^64 accommodates just shy of 10^19 in signed integers. So, even if your database had a justification for thousands of a cent transactions (not intermediate results, but recordable transactions), you'd still need to have…

To be fair, I used to think like this too, but chatting with multiple large exchanges/brokerages made us realize this was a thing.

> less than 10^15 cents

There are systems that don't work in terms of cents (cf. the examples of issues in many of the comments here), or even in thousandths of a cent, but with significantly more precision.

Literally, in other words:

Where you run into problems then, with 10 ^ n integer scaling, is when n is large. When n is large, you aren't left with sufficient room in the remaining bytes to represent the whole-number part. In trading systems, for instance, you can easily hit 10 ^ 10 to represent fractional traded prices.

Concretely, if you need to scale by 10 ^ 10, then your whole-number part is 2 ^ 64 / 10 ^ 10 = 1,844,674,407, which isn't terribly large.

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