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Re: Float behaviour
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Re: Float behaviour


  • Subject: Re: Float behaviour
  • From: ObjM2 <email@hidden>
  • Date: Tue, 23 Aug 2005 02:59:37 +0900


On Aug 23, 2005, at 2:19 AM, Richard Gray wrote:

If I were to convert $1 at an exchange rate of 1.2, I'd expect to get
1.2 units of the new currency yes?  According to my currency converter
however, 1 x 1.2 = 1.200000047683716

Can someone explain this behaviour to me and how to avoid it?

You'll need a BCD library (BCD = binary coded decimals => no rounding errors)


http://en.wikipedia.org/wiki/Binary-coded_decimal

However, there is no support for BCDs amongst the generally available C libraries, so you'll have to roll your own or use a different language. COBOL uses BCDs by default. p1 Modula-2 for the Mac has built-in BCD support, but no Cocoa support and it's not free either.

ObjM2 when finished, will also have BCDs built-in, but that won't help you right now.

It shouldn't be all too difficult to write a Cocoa class for BCDs though.





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