Comments on: Suspect Rounding In .Net http://www.gringod.com/2005/10/28/suspect-rounding-in-net/ Randomised nonsense. Fri, 04 Nov 2011 08:49:25 +0000 hourly 1 http://wordpress.org/?v=3.2.1 By: plafond http://www.gringod.com/2005/10/28/suspect-rounding-in-net/comment-page-1/#comment-12008 plafond Fri, 16 Jun 2006 15:58:51 +0000 http://www.gringod.com/2005/10/28/suspect-rounding-in-net/#comment-12008 The problem with the Double value is that it is a binary representation (0's and 1's). Binary representations cannot represent every possible decimal value. It's very important to understand that in the same way that you can't represent a third exactly in a (finite) decimal expansion, there are lots of numbers which look simple in decimal, but which have long or infinite expansions in a binary expansion. This means that (for instance) a binary floating point variable can't have the exact value of decimal 0.1. See "http://www.yoda.arachsys.com/csharp/floatingpoint.html" for more info If you need to guaranty precision use decimal. Microsoft documentation state "The Decimal value type is appropriate for financial calculations requiring large numbers of significant integral and fractional digits and no round-off errors." The problem with the Double value is that it is a binary representation (0′s and 1′s).

Binary representations cannot represent every possible decimal value.

It’s very important to understand that in the same way that you can’t represent a third exactly in a (finite) decimal expansion, there are lots of numbers which look simple in decimal, but which have long or infinite expansions in a binary expansion. This means that (for instance) a binary floating point variable can’t have the exact value of decimal 0.1.

See “http://www.yoda.arachsys.com/csharp/floatingpoint.html” for more info

If you need to guaranty precision use decimal. Microsoft documentation state “The Decimal value type is appropriate for financial calculations requiring large numbers of significant integral and fractional digits and no round-off errors.”

]]> By: GrinGod [dot] Com » Blog Archive » Double Imprecision In .Net http://www.gringod.com/2005/10/28/suspect-rounding-in-net/comment-page-1/#comment-10107 GrinGod [dot] Com » Blog Archive » Double Imprecision In .Net Wed, 01 Feb 2006 18:26:55 +0000 http://www.gringod.com/2005/10/28/suspect-rounding-in-net/#comment-10107 [...] 7:26 pm I’ve spouted on about this previously on my blog but I thought it was about time I posted some code that demonstrates some of the problems we’re up against. The problem seems to be that under certain circumstances the .Net Double data type loose its precision and gives you a number that you weren’t expecting. The chances are that the error will be out by 0.00000000000001, but that might be enough to cause an error. [...] [...] 7:26 pm I’ve spouted on about this previously on my blog but I thought it was about time I posted some code that demonstrates some of the problems we’re up against. The problem seems to be that under certain circumstances the .Net Double data type loose its precision and gives you a number that you weren’t expecting. The chances are that the error will be out by 0.00000000000001, but that might be enough to cause an error. [...]

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