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

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

#121

Post by projektfu »

TheCoelacanth wrote: post #94
tylergetsay wrote: post #86

Earlier quoted context omitted.

For simple accounting I've always used integers and done all operations in cents, only converting on the frontend. what's my downside here? I guess it wouldn't support unit prices less than a penny

Also many types of operations could give you the wrong result from incorrect rounding. E.g. let's say you're calculating 10% of $1.01 ten times and adding the result together. The correct result is $1.01, but with your method you will get $1.00.

The correct answer will depend on the specifics of your environment. In some places, tax is calculated per line item. If you go to a dollar store and buy 10 items with 7.3% sales tax, it adds up without those 0.3¢ bits. In other places, the tax is supposed to be calculated on the total for the tax category in the sale. If you wanted to keep it by line item you'd need the extra digits of precision.

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

#122

Post by frankreyes »

onetimeuse92304 wrote: post #24

Specialising in financial software, over the past 2 decades I have been fighting over this with countless people, teams and companies. For accounting you should only ever use arbitrary precision math library with ability to specify rounding rules. If your programming environment/language does not have one, it is unsuitable to be used for accounting, billing, invoicing, payments, etc. Having the underlying library is,…

Many decades ago I worked in a Java team who they were using some money as a double and some as a BigDecimal. When I asked why, ... they said that at the start they didn't think they'd have any issue with doubles. Years later and still had lots of tech debt because manually rounding doubles to BigDecimal.

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

#123

Post by kawhah »

onetimeuse92304 wrote: post #73
tgv wrote: post #67

Earlier quoted context omitted.

For very simple billing, arbitary precision sounds like overkill, as do rounding, and order of operations.

Oh, sure, because when you are a small company you don't care that people get correct invoices. I can certainly sympathise with this stance. There is about a billion things you can do better but you have limited time to do anything so you have to prioritise. And if one invoice in ten thousand is incorrect by one cent, and only one client in ten thousand who received the wrong invoice will actually find it out, then i…

Let me guess, the last 10 times you had to move jobs it was because of a difference in opinion with your boss about the importance of correcting one-cent-errors in one invoice out of every ten thousand?

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

#124

Post by keepamovin »

Reserve Bank of Zimbabwe "100 Trillion Dollars" hahahahaha

LOL. Is that real? OMG, that's incredible. Image if this trend kept going: what sign of humanity that new SI units need to be minted first because inflation drives currencies to insane new denominations, rather than cat videos, IoT and porn bulge yottabytes out of bounds?

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

#125

Post by seanhunter »

rvnx wrote: post #53
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…

I had such case too, the solution is simple: round in favor of the bank / financial institution you are working for

That is absolutely not how it works. Rounding is exactly specified in the underlying contract always and you need to implement the correct rounding. For example, here is the rounding table for compounding calculations in the ISDA definitions (these are very standard for a wide range of contracts, but this particular table is for various overnight swap rates used in interest rate derivatives)[1].

[1] https://globalmarkets.cib.bnpparibas/app/uploads/sites/4/202...

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

#126

Post by jkestner »

onetimeuse92304 wrote: post #48
Aardwolf wrote: post #44

Earlier quoted context omitted.

Would IEEE decimal128 be sufficient (instead of arbitrary precision)? "Formally introduced in IEEE 754-2008, it is intended for applications where it is necessary to emulate decimal rounding exactly, such as financial and tax computations." https://en.wikipedia.org/wiki/Decimal128_floating-point_form...

Hypothetical solutions that do not exist are none of my concern. Did you know different countries and different currencies have different rounding rules, for example for tax-related calculations? Does "IEEE decimal128" support this? Unless you can get all countries on our planet to agree on a single standard, any solution that does not allow specifying rounding rules is pretty much useless (unless you want to impleme…

I'm going through this pain right now in helping my kid with homework in rounding and discovering my internalized rules are different from what they're being taught now. EXACT same pain as yours, depending on the precision and rounding rules of your pain scale.

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

#127

Post by jefftk »

runeks wrote: post #77
Shrezzing wrote: post #50

The hyperinflation example is quite interesting because: 1) If it happens, it happens rapidly, and you don't want to implement this in a hurry 2) If it happens, the global economy could well be melting down, and your financial institution will have other priorities to attend to 3) Retaining existing staff, and hiring new engineers, will be challenging at best You really don't want to be implementing this change in th…

I think it's the worst example. I very much doubt we will ever see the price of, say, a car approach a billion billion dollars (or cents). It's too many zeros for people to work with on a daily basis. I think what will happen is that, at regular intervals, the old hyper-inflated currency will be replaced with a new currency that's, say, 2^32 times less than the original one. Besides, if you think a billion billions m…

Before 2009 would you have predicted that a 100 Trillion Dollar bill would never be issued by a central bank?

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

#128

Post by SoftTalker »

im3w1l wrote: post #113
onetimeuse92304 wrote: post #24

Specialising in financial software, over the past 2 decades I have been fighting over this with countless people, teams and companies. For accounting you should only ever use arbitrary precision math library with ability to specify rounding rules. If your programming environment/language does not have one, it is unsuitable to be used for accounting, billing, invoicing, payments, etc. Having the underlying library is,…

> I have never in my life joined a software project for any organisation that was able to do basic arithmetic on money correct This observation should tell you that's it actually quite viable to be off as long as the errors are small enough.

Yeah even in university in my intro-level accounting classes they said in the real world nobody cares about discrepancies less than a dollar (and that amount scales with the size of the business). I don't know if that's actually true and I wasn't an accounting major so I don't know what they said in the more advanced classes.

But if I imagine myself as a business owner I would be annoyed with my accounting firm if they spent billable hours chasing down a discrepancy of a few pennies.

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

#129

Post by GoToRO »

Vvector wrote: post #101
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…

Sounds like the start of a movie script

Office Space

https://youtu.be/yZjCQ3T5yXo?si=xGGrxafG2zzA0IIR

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

#130

Post by devmor »

im3w1l wrote: post #113
onetimeuse92304 wrote: post #24

Specialising in financial software, over the past 2 decades I have been fighting over this with countless people, teams and companies. For accounting you should only ever use arbitrary precision math library with ability to specify rounding rules. If your programming environment/language does not have one, it is unsuitable to be used for accounting, billing, invoicing, payments, etc. Having the underlying library is,…

> I have never in my life joined a software project for any organisation that was able to do basic arithmetic on money correct This observation should tell you that's it actually quite viable to be off as long as the errors are small enough.

As someone who works in fintech, my observation is not that the caveat is "as long as the errors are small enough" but rather "as long as whoever governs the business logic is aware of the impact".

The size of the errors almost always is a large factor in their decision, but ultimately the software we write exists to serve the needs of the business, and if the business decides that larger errors are okay for some reason, then so be it.

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