Accounting has the concept of materiality. But you still want the figures to tally to the last cent.
One way to do this is to separate the computation/storage and presentation layer: use integers to store values as cents for computation/storage and only convert to dollars+cents on display. But then someone might suddenly demand three digits after the decimal point and you cannot go about changing every stored value just because the logic changed in one part of the application. So, using decimals is the safer choice.
I prefer integers for my plain text ledger software though because the format is in my control.
This gets tricky when it comes to dealing with currency conversion. On my most recent credit card bill, foreign currency transactions show an exchange rate with 10 digits of precision.
When implementing currency with integers, actually with fixed-point numbers, there is no difficulty in having an exchange rate with the same precision as the integer format, i.e. up to 18-19 digits for 64-bit integers.
You just have to implement the conversion function carefully, i.e. the exchange ratio would actually be represented not by a single number, but by a ratio of suitable integers, to ensure no loss of precision during the conversion done by exact multiplication with extended double-word result and then division.
sieve · · focus · HN ↗
One way to do this is to separate the computation/storage and presentation layer: use integers to store values as cents for computation/storage and only convert to dollars+cents on display. But then someone might suddenly demand three digits after the decimal point and you cannot go about changing every stored value just because the logic changed in one part of the application. So, using decimals is the safer choice.
I prefer integers for my plain text ledger software though because the format is in my control.
PaulDavisThe1st · · focus · HN ↗
adrian_b · · focus · HN ↗
You just have to implement the conversion function carefully, i.e. the exchange ratio would actually be represented not by a single number, but by a ratio of suitable integers, to ensure no loss of precision during the conversion done by exact multiplication with extended double-word result and then division.