3 ms·

> You have to do many, many additions and multiplications before you get a result which has accumulated so much error that it is now closer to the wrong penny

> You have to do many, many additions and multiplications before you get a result which has accumulated so much error that it is now closer to the wrong penny > You can counteract this problem by correcting intermediate results to that floating-point value which is closest to exact penny result The argument seems to be "floats are okay, as long as you're careful", but forgetting to round the number in between a large number of operations is a probable mistake. Using decimals would make such a mistake impossible.

kazinator 4y ago
Even with a decimal representation, there are situations where you have to remember to round to a cent. Decimals are software libs; what could go wrong? More people use the floating-point instructions of a popular CPU than any given decimal library. If you're starting from scratch, it's probably a lot less work to write (test and debug) a Money class based on floating-point, whose overloaded math operations do the required rounding (so that code using the class cannot forget) than to make a Money class based on decimal arithmetic. (The last time I wrote an accounting system, I made a Money class based on integers. It could be retargeted to other representations easily. I could make the change and compare the ledger totals and other reports to see if there is a difference.)
- bheadmaster 4y ago
  > Decimals are software libs; what could go wrong? Bugs in libraries do exist, but it's much easier to fix a bug in one place, than to track down every single line where floating point operations could misbehave.
- lmm 4y ago
  > More people use the floating-point instructions of a popular CPU than any given decimal library. Perhaps, but how many of the former are in a position to notice accuracy issues? I have more faith in a reputable decimal library than your average FPU, frankly.

kazinator 4y ago

Even with a decimal representation, there are situations where you have to remember to round to a cent. Decimals are software libs; what could go wrong? More people use the floating-point instructions of a popular CPU than any given decimal library. If you're starting from scratch, it's probably a lot less work to write (test and debug) a Money class based on floating-point, whose overloaded math operations do the required rounding (so that code using the class cannot forget) than to make a Money class based on decimal arithmetic. (The last time I wrote an accounting system, I made a Money class based on integers. It could be retargeted to other representations easily. I could make the change and compare the ledger totals and other reports to see if there is a difference.)

bheadmaster 4y ago
> Decimals are software libs; what could go wrong? Bugs in libraries do exist, but it's much easier to fix a bug in one place, than to track down every single line where floating point operations could misbehave.
lmm 4y ago
> More people use the floating-point instructions of a popular CPU than any given decimal library. Perhaps, but how many of the former are in a position to notice accuracy issues? I have more faith in a reputable decimal library than your average FPU, frankly.