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# I need to manage more than 15 digits of precision in my Visual C++ program and libraries

Posted on 2011-02-28
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Hi,

I have a program and libraries written in Visual C++ 2005 where i use variables of type double. So far i have been working with this data type with the maximum 15 digits of precision but now i have a request from my customer for supporting 16, 17 and more digits of precision. I don't know how to do this or even if that is possible.

What can i do?
Should i use the boost libraries?
Write my own type and change the data types all over the code (thousands of lines involved) ?

Thanks and regards,

Johann
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Question by:JohannRamon

LVL 86

Accepted Solution

jkr earned 500 total points
ID: 35002856
It's definitely possible - check out e.g.

NTL (http://www.shoup.net/ntl/): arbitrary length integers, vectors/matrices/polynomials over integers and over finite fields.
Apfloat (http://www.apfloat.org/apfloat/): a C++ High Performance Arbitrary Precision Arithmetic Package
MUNTL (http://sourceforge.net/projects/muntl/): Multiprecision unsigned number template library
LiDIA (http://www.cdc.informatik.tu-darmstadt.de/TI/LiDIA/): A library for computational number theory. Provides a collection of highly optimized implementations of various multiprecision data types and time-intensive algorithms.
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LVL 32

Expert Comment

ID: 35005249
it would be not so difficult to use own type highdouble instead of double in your code. you can do such a substitution in very short time with case sensitive and full-word replacement. then make a central typedef double highdouble; and your programs should build. you then can decide how to implement highdouble, either made by your own for example based on 64-bit integer or using an appropriate type of a foreign library as base.

Sara
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Author Comment

ID: 35017500
Hi,

jkr: I have checked the libraries and so far NTL types (xdouble or RR) look like my best solution. It looks like the library i already have "boost" doesn't have an appropriate data type.

Sara: It looks like the best path for this large amount of code is the search-replace of the data type. If i include the foreign library it would still be necessary to make the "typedef double highdouble"?

Thanks again and regards,

Johann
0

LVL 32

Expert Comment

ID: 35019713
you probably then would replace the typedef by

typedef  long_double_from_library highdouble;

or in case the new (class) type would not provide an interface so that it could substitute a double, you would implement the type highdouble yourself taking the type from the library as a base.

Sara
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LVL 2

Author Comment

ID: 35060797
Hi,

Funny as it sounds, my management wants a "commercial" solution because they feel it is necessary to have a "provider" which can give us support and warranties backed up with a contract (the perceived risk of precision errors is too high for us to assume it alone).

I´m sorry for this added condition. Any suggested option?

Thanks again and regards,

Johann
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LVL 53

Expert Comment

ID: 35321646
This question has been classified as abandoned and is being closed as part of the Cleanup Program. See my comment at the end of the question for more details.
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