Comments on: Once and for all: Do not use double for money http://codemonkeyism.com/once-and-for-all-do-not-use-double-for-money/ Wed, 09 May 2012 22:39:34 +0000 hourly 1 http://wordpress.org/?v=3.3.2 By: andrew http://codemonkeyism.com/once-and-for-all-do-not-use-double-for-money/comment-page-1/#comment-341153 andrew Mon, 11 Oct 2010 17:43:12 +0000 http://stephan.reposita.org/archives/2008/01/11/once-and-for-all-do-not-use-double-for-money/#comment-341153 Hi Stephan, This is a good point which I try to adhere to in my applications, but I am curious how you deal with performance issues associated with large sets of data. BigDecimal does not perform well when you have 1+ million calculations to do consistently (like multiple times for every execution of the application). This is a real life scenario I am describing. Have you found anything that utilizes banker's rounding but still comes close to the performance of operating on primitive doubles? Hi Stephan,
This is a good point which I try to adhere to in my applications, but I am curious how you deal with performance issues associated with large sets of data. BigDecimal does not perform well when you have 1+ million calculations to do consistently (like multiple times for every execution of the application). This is a real life scenario I am describing. Have you found anything that utilizes banker’s rounding but still comes close to the performance of operating on primitive doubles?

]]> By: Ger http://codemonkeyism.com/once-and-for-all-do-not-use-double-for-money/comment-page-1/#comment-285539 Ger Wed, 21 Apr 2010 20:56:26 +0000 http://stephan.reposita.org/archives/2008/01/11/once-and-for-all-do-not-use-double-for-money/#comment-285539 Today I came back to this posting. I'm maintaining an app made by other people no longer in the company, and there is an issue with money rounding - they used Double. I'm so pissed off I have to deal with this!!! So yeah folks, I guess this posting is great advice. Today I came back to this posting. I’m maintaining an app made by other people no longer in the company, and there is an issue with money rounding – they used Double. I’m so pissed off I have to deal with this!!!
So yeah folks, I guess this posting is great advice.

]]> By: stephan http://codemonkeyism.com/once-and-for-all-do-not-use-double-for-money/comment-page-1/#comment-226234 stephan Fri, 27 Feb 2009 14:16:07 +0000 http://stephan.reposita.org/archives/2008/01/11/once-and-for-all-do-not-use-double-for-money/#comment-226234 Alex: Sure? Looking at page 491 of Patterns of Enterprise Application Architecture he explicitly discourages the use of floats and suggests using long (See google book search). Alex: Sure?

Looking at page 491 of Patterns of Enterprise Application Architecture he explicitly discourages the use of floats and suggests using long (See google book search).

]]> By: Alex http://codemonkeyism.com/once-and-for-all-do-not-use-double-for-money/comment-page-1/#comment-226231 Alex Fri, 27 Feb 2009 13:46:58 +0000 http://stephan.reposita.org/archives/2008/01/11/once-and-for-all-do-not-use-double-for-money/#comment-226231 funny enough, but Fowler did use double for money amount in his examples :-) funny enough, but Fowler did use double for money amount in his examples :-)

]]> By: FEZ http://codemonkeyism.com/once-and-for-all-do-not-use-double-for-money/comment-page-1/#comment-48945 FEZ Mon, 14 Jan 2008 16:18:34 +0000 http://stephan.reposita.org/archives/2008/01/11/once-and-for-all-do-not-use-double-for-money/#comment-48945 http://en.wikipedia.org/wiki/Rounding#Round-to-even_method: "The origin of the term bankers' rounding is more obscure. If this rounding method was ever a standard in banking, the evidence has proved extremely difficult to find. To the contrary, section 2 of the European Commission report The Introduction of the Euro and the Rounding of Currency Amounts [2] suggests that there had previously been no standard approach to rounding in banking." http://en.wikipedia.org/wiki/Rounding#Round-to-even_method:

“The origin of the term bankers’ rounding is more obscure. If this rounding method was ever a standard in banking, the evidence has proved extremely difficult to find. To the contrary, section 2 of the European Commission report The Introduction of the Euro and the Rounding of Currency Amounts [2] suggests that there had previously been no standard approach to rounding in banking.”

]]> By: BigDecimal money cookbook at Stephans Blog http://codemonkeyism.com/once-and-for-all-do-not-use-double-for-money/comment-page-1/#comment-48919 BigDecimal money cookbook at Stephans Blog Mon, 14 Jan 2008 12:55:59 +0000 http://stephan.reposita.org/archives/2008/01/11/once-and-for-all-do-not-use-double-for-money/#comment-48919 [...] No signal, no noise. « Once and for all: Do not use double for money [...] [...] No signal, no noise. « Once and for all: Do not use double for money [...]

]]> By: stephan http://codemonkeyism.com/once-and-for-all-do-not-use-double-for-money/comment-page-1/#comment-48897 stephan Mon, 14 Jan 2008 10:00:53 +0000 http://stephan.reposita.org/archives/2008/01/11/once-and-for-all-do-not-use-double-for-money/#comment-48897 ROUND_HALF_EVEN is called fair rounding because it distributes the error. It's also called bankers rounding. http://en.wikipedia.org/wiki/Rounding#Round-to-even_method "Rounding mode to round towards the "nearest neighbor" unless both neighbors are equidistant, in which case, round towards the even neighbor. Behaves as for ROUND_HALF_UP if the digit to the left of the discarded fraction is odd; behaves as for ROUND_HALF_DOWN if it's even. Note that this is the rounding mode that minimizes cumulative error when applied repeatedly over a sequence of calculations." http://java.sun.com/j2se/1.5.0/docs/api/java/math/BigDecimal.html#ROUND_HALF_EVEN ROUND_HALF_EVEN is called fair rounding because it distributes the error. It’s also called bankers rounding.

http://en.wikipedia.org/wiki/Rounding#Round-to-even_method

“Rounding mode to round towards the “nearest neighbor” unless both neighbors are equidistant, in which case, round towards the even neighbor. Behaves as for ROUND_HALF_UP if the digit to the left of the discarded fraction is odd; behaves as for ROUND_HALF_DOWN if it’s even. Note that this is the rounding mode that minimizes cumulative error when applied repeatedly over a sequence of calculations.”

http://java.sun.com/j2se/1.5.0/docs/api/java/math/BigDecimal.html#ROUND_HALF_EVEN

]]> By: FEZ http://codemonkeyism.com/once-and-for-all-do-not-use-double-for-money/comment-page-1/#comment-48885 FEZ Mon, 14 Jan 2008 09:10:10 +0000 http://stephan.reposita.org/archives/2008/01/11/once-and-for-all-do-not-use-double-for-money/#comment-48885 I don't know about USA, but in Europe you would use ROUND_HALF_UP for money rounding!? I don’t know about USA, but in Europe you would use ROUND_HALF_UP for money rounding!?

]]> By: stephan http://codemonkeyism.com/once-and-for-all-do-not-use-double-for-money/comment-page-1/#comment-48880 stephan Mon, 14 Jan 2008 08:11:39 +0000 http://stephan.reposita.org/archives/2008/01/11/once-and-for-all-do-not-use-double-for-money/#comment-48880 @Greg: I have the same feeling. Developers using double or float do use the wrong type in most cases except for 3D graphics or statistics. @Greg: I have the same feeling. Developers using double or float do use the wrong type in most cases except for 3D graphics or statistics.

]]> By: Finds of the Week - December 13, 2008 » Chinh Do http://codemonkeyism.com/once-and-for-all-do-not-use-double-for-money/comment-page-1/#comment-48868 Finds of the Week - December 13, 2008 » Chinh Do Mon, 14 Jan 2008 06:36:25 +0000 http://stephan.reposita.org/archives/2008/01/11/once-and-for-all-do-not-use-double-for-money/#comment-48868 [...] Stephan advised to use the "money" data type to store currency amounts instead of doubles. For good reasons. [...] [...] Stephan advised to use the "money" data type to store currency amounts instead of doubles. For good reasons. [...]

]]> By: Greg Miller http://codemonkeyism.com/once-and-for-all-do-not-use-double-for-money/comment-page-1/#comment-48821 Greg Miller Mon, 14 Jan 2008 00:19:44 +0000 http://stephan.reposita.org/archives/2008/01/11/once-and-for-all-do-not-use-double-for-money/#comment-48821 Quote: -------------------------- I always distribute as [3.33, 3.33, 3.33] and then deposit 0.01 into my own secret account. -------------------------- Just make sure you don't mess up on some mundane detail like putting a decimal point in the wrong place. But seriously, it's been my opinion for a while that using float or double should cause a compiler warning optionally suppressed by a compiler flag. I believe the only place a typical programmer would run into floats being used correctly would be 3D graphics programming. Quote:
————————–
I always distribute as [3.33, 3.33, 3.33] and then deposit 0.01 into my own secret account.
————————–

Just make sure you don’t mess up on some mundane detail like putting a decimal point in the wrong place.

But seriously, it’s been my opinion for a while that using float or double should cause a compiler warning optionally suppressed by a compiler flag. I believe the only place a typical programmer would run into floats being used correctly would be 3D graphics programming.

]]> By: stephan http://codemonkeyism.com/once-and-for-all-do-not-use-double-for-money/comment-page-1/#comment-48673 stephan Sat, 12 Jan 2008 14:33:05 +0000 http://stephan.reposita.org/archives/2008/01/11/once-and-for-all-do-not-use-double-for-money/#comment-48673 The comic hero, I´m really honoured. A lot of people tried this, most of them got caught when getting greedy :-) The comic hero, I´m really honoured.

A lot of people tried this, most of them got caught when getting greedy :-)

]]> By: Eric Burke http://codemonkeyism.com/once-and-for-all-do-not-use-double-for-money/comment-page-1/#comment-48653 Eric Burke Sat, 12 Jan 2008 12:43:46 +0000 http://stephan.reposita.org/archives/2008/01/11/once-and-for-all-do-not-use-double-for-money/#comment-48653 I always distribute as [3.33, 3.33, 3.33] and then deposit 0.01 into my own secret account. I always distribute as [3.33, 3.33, 3.33] and then deposit 0.01 into my own secret account.

]]> By: stephan http://codemonkeyism.com/once-and-for-all-do-not-use-double-for-money/comment-page-1/#comment-48510 stephan Fri, 11 Jan 2008 15:06:18 +0000 http://stephan.reposita.org/archives/2008/01/11/once-and-for-all-do-not-use-double-for-money/#comment-48510 @digital.alterego: Fowler calls it allocate I guess. You have 3 people and need to distribute (allocate) 10 EUR to them. 10/3 = 3.33 in cents, which means 1 cent is lost. Distributing 10 EUR correctly will result in 3 buckets [3.33, 3.33, 3.34]. @digital.alterego: Fowler calls it allocate I guess. You have 3 people and need to distribute (allocate) 10 EUR to them. 10/3 = 3.33 in cents, which means 1 cent is lost. Distributing 10 EUR correctly will result in 3 buckets [3.33, 3.33, 3.34].

]]> By: digital.alterego http://codemonkeyism.com/once-and-for-all-do-not-use-double-for-money/comment-page-1/#comment-48504 digital.alterego Fri, 11 Jan 2008 14:12:01 +0000 http://stephan.reposita.org/archives/2008/01/11/once-and-for-all-do-not-use-double-for-money/#comment-48504 What do you mean with "Use a distribute algorithm to distribute money to severel slots without loosing cents."? Could you please explain this further? Anyway thanks for the links, good discussions there. What do you mean with “Use a distribute algorithm to distribute money to severel slots without loosing cents.”? Could you please explain this further? Anyway thanks for the links, good discussions there.

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