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jamesleighe

Floating Point Constants

12 posts in this topic

(in c++)

In my code I have a special type that allows me to switch between 'float' and 'double' for at least some portions of the code.

The problem is constants like '0.015' are default double, and generate tonnes of warnings when I switch to 'float' mode. Because of expressions like 'floatn = 1.5'. However, if I append an 'f' to the end of every constant then I could be removing some of the accuracy benefits of doubles in double mode.

What should I do to get rid of these warnings and still allow me to have the benefit of doubles when I compile it with 'floatn' typedef'd to 'float'?

Thank!
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Definitely, however that would create thousands of ugly ifdefs in my application so a more elegant solution is called for.
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You could do something like this:
[code]#define USE_FLOAT

#ifdef USE_FLOAT
typedef float Real;
#define CREAL(x) x ## f
#else
typedef double Real;
#define CREAL(x) x
#endif

const Real PI = CREAL(3.14);[/code]
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Then refactor your code so that it's not full of magic numbers?

Create a function that returns the proper data type, and use an ifdef to define it? Feed it a string, and it will return either a float or a double, depending on your definitions.

edit: Wow, ninja'd Edited by Daaark
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[quote name='Daaark' timestamp='1343887823' post='4965417']
Then refactor your code so that it's not full of magic numbers?
[/quote]

I try not to use magic numbers, the vast majority of the warnings come from initialization and simple arithmetic.


Thanks everyone I'll give your ideas a shot, but I'm still open to more suggestions!
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[source]
typedef float real; // or double

real x = real(23.0);
[/source]

I'm not sure why that didn't occur to me last night...

And yeah I'm being anal about precision even though its hardly an issue but it helps for arithmetic with pi or simply 1/3 like the above poster said. Edited by James Leighe
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Very true, I wouldn't recommend it for everyone.

It's more of an experiment but it's not much more trouble than not doing it (once the changes are made to existing code) so I guess it's a bit of future proofing.
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IMO you should be using templates if you need to write code that works with any type. This allows you to use multiple types and change them later without affecting existing code. Besides float and double, it's also possible that you may use one of the integer types, complex, a quaternion type, a vector or matrix type, etc. For example, if you have a generic vector type then you can use vec<unsigned char, 4> or vec_4<unsigned char> to store image data and manipulate it in a convenient manner (although you may also have to implement casts).
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