5 ms·

Using floats to represent currency is a big no-no. Floats have limited precision, and some numbers aren't representable by floats. Go try adding 0.1 to itself o

Using floats to represent currency is a big no-no. Floats have limited precision, and some numbers aren't representable by floats. Go try adding 0.1 to itself over and over again in your favorite implementation. It is better to represent as integers or fixed-precision numbers. That way, you are dealing with exact quantities.

negamax 13y ago
To me it seems like floats are being converted to int and then code is working with it. I don't think this will create an issue unless the int is overflowing. Any failing testcase?
SixSigma 13y ago
> some numbers aren't representable by floats an infinite number of them in fact
- deleted 13y ago
  [deleted]
- SixSigma 13y ago
  Turing proved there's an uncountable set of numbers that cannot even be computed let alone represented
skj 13y ago
Could make all the same arguments against integers: - Limited precision, - Some numbers aren't representable, - Go try adding 1 to itself over and over again. That said, yes, floats are a bad idea for financial arithmetic.
- thaumasiotes 13y ago
  You can make the same arguments against integers, but you'd need to be willfully blind to the context of the discussion. There are no monetary quantities that can't be represented as integers. Using a scheme that can't represent 1/3 to record numbers for which 1/3 is an illegal value doesn't present any practical or theoretical problems.
  - skj 13y ago
    My point was that the arguments presented were not the reasons that using floats to handle finance was a bad idea. Since, as I showed, they also applied to integers.
    - ufo 13y ago
      Sheesh, stop being so pedantic. Unlike computers, humans can infer extra meaning from the context around a sentence.
andruby 13y ago
As an example in Ruby (2.1.1): x = 0.1 #=> 0.1 10.times { x+=0.1 } #=> 10 x #=> 1.0999999999999999
klibertp 13y ago
Works in Racket (and should in other Schemes): -> (for/sum ([_ (in-range 10)]) (/ 1 10)) 1 Yeah, I know, I'm cheating - `(/ 1 10)` returns a rational? which is not flonum?. Using `0.1` makes it inexact like it should be: -> (for/sum ([_ (in-range 10)]) 0.1) 0.9999999999999999
rodgerd 13y ago
It's even better to represent as binary coded decimal, Ulrich Drepper's opinions notwithstanding.
orthecreedence 13y ago
That's why I like lisp: (/ 10 17) => 10/17 (+ (/ 10 17) (/ 4 9)) => 158/153 =]

negamax 13y ago

To me it seems like floats are being converted to int and then code is working with it. I don't think this will create an issue unless the int is overflowing. Any failing testcase?

SixSigma 13y ago

> some numbers aren't representable by floats an infinite number of them in fact

deleted 13y ago
[deleted]
SixSigma 13y ago
Turing proved there's an uncountable set of numbers that cannot even be computed let alone represented

skj 13y ago

Could make all the same arguments against integers: - Limited precision, - Some numbers aren't representable, - Go try adding 1 to itself over and over again. That said, yes, floats are a bad idea for financial arithmetic.

thaumasiotes 13y ago
You can make the same arguments against integers, but you'd need to be willfully blind to the context of the discussion. There are no monetary quantities that can't be represented as integers. Using a scheme that can't represent 1/3 to record numbers for which 1/3 is an illegal value doesn't present any practical or theoretical problems.
- skj 13y ago
  My point was that the arguments presented were not the reasons that using floats to handle finance was a bad idea. Since, as I showed, they also applied to integers.
  - ufo 13y ago
    Sheesh, stop being so pedantic. Unlike computers, humans can infer extra meaning from the context around a sentence.

andruby 13y ago

As an example in Ruby (2.1.1): x = 0.1 #=> 0.1 10.times { x+=0.1 } #=> 10 x #=> 1.0999999999999999

klibertp 13y ago

Works in Racket (and should in other Schemes): -> (for/sum ([_ (in-range 10)]) (/ 1 10)) 1 Yeah, I know, I'm cheating - `(/ 1 10)` returns a rational? which is not flonum?. Using `0.1` makes it inexact like it should be: -> (for/sum ([_ (in-range 10)]) 0.1) 0.9999999999999999

rodgerd 13y ago

It's even better to represent as binary coded decimal, Ulrich Drepper's opinions notwithstanding.

orthecreedence 13y ago

That's why I like lisp: (/ 10 17) => 10/17 (+ (/ 10 17) (/ 4 9)) => 158/153 =]