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0 pointsSonOfLilit9mo ago0 comments

You can make money modeling buy/sell decisions in floats and then having the bank execute them, but if the bank models your account as a float and loses a cent here and there, it will be sued into bankruptcy.

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jcranmer9mo ago

A double-precision float has ~16 decimal digits of precision. Which means as long as your bank account is less than a quadrillion dollars, it can accurately store the balance to the nearest cent.

kccqzy9mo ago

You will not lose a cent here and there just by using float64, for the range of values that banks deal with. For added assurance, just round to the nearest cent after each operation.

kbolino9mo ago

You can round to the nearest .0078125 (1/128) but not to the nearest .01 (1/100) because that number cannot be represented in float64.

To round to the nearest cent, you would need to make cents your units (i.e. the quantity "1 dollar" would be represented as 100 instead of 1.0).

nurettin9mo ago

Within the general context of this discussion, "cannot be represented" is a red herring.

You don't need to have a representation of the exact number 0.1 if you can tolerate errors after the 7th decimal (and it turns out you can). And 0.1+0.1+0.1 does not have to be comparable with 0.3 using operator==. You have an is_close function for that. And accumulation is not an issue because you have rounding and fma for that.

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