Re: Crazy floats
Re: Crazy floats
- Subject: Re: Crazy floats
- From: Ricky Sharp <email@hidden>
- Date: Fri, 23 Jul 2004 08:39:49 -0500
On Friday, July 23, 2004, at 08:32AM, Lorenzo <email@hidden> wrote:
>
I have a floats with 3 values but if I add many times the value 0.2 to one
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item, it gets some decimal value more. Instead of -0.693000, I get
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-0.693001. Why do I get the 1 at the end?
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float positions[3];
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>
positions[0] = -0.693000; // currentPoint
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positions[1] = positions[0] + 2; // endPoint
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positions[2] = increment = 0.2; // increment
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>
so I try to add the increment to the "currentPoint" value until it is equal
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to the "end" value.
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while(positions[0] != positions[1]){
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positions[0] += positions[2];
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NSLog(@"currentPoint %f, end %f, increm %f",
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positions[0], positions[1], positions[2]);
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}
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>
And since they are never equal, this produces an "infinite loop" (I am not
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speaking about the Apple address).
This is why a course in "numerical analysis" is very important :) Not all real-world values can be represented by floating point values.
This is not unique to Cocoa, or specifically to the float type, but to any floating point value. You should _never_ perform exact comparissons. Instead, use either an integral loop variant (e.g int, long), or use >, >=, <, or <= comparissons.
Rick Sharp
Instant Interactive(tm)
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