[boost] Boost Test Library: general floating point comparisons

From: Dave Steffen (dgsteffen_at_[hidden])
Date: 2007-02-13 16:36:21

Hi folks,

This is probably a question aimed at Gennadiy Rozental, but it may be
of interest to the community in general.

We've been using the boost test library for about a year and a half
now, and are happy customers.  I'm revamping our unit test framework
(e.g. revisiting the way we use boost test), and am specifically
looking at the floating point comparisons.

One thing that I'm changing / hacking is the use of percentages to
specify tolerance.  We usually want answers to agree to (say) 1 part
in 10^-12, and remembering to multiply or divide that by 100 is
annoying.  To this end, I'm defining our own set of comparison
functions and macros, still using the stuff in ttdetail (e.g. fpt_abs
and save_fpt_division).

Fine.  Now, we want to be able to compare more complicated
mathematical objects, such as vectors and matrices.

After some thought, we decided the responsibility for providing such
functions is the responsibility of the mathematical object, not the
unit test framework.  That is to say, a function "relative difference
between matrices" should be in Matrix.h, not some unit test thing.

Which leads to the idea of Matrix.h #including
"boost/test/floating_point_comparison.hpp", which strikes me as rather
odd.  My first impulse was to copy/pull the relevent code out of
floating_point_comparison.hpp and stick it in some more convenient
place, where mathematical objects could use those functions to
implement their own comparision functions.

Might this be a common idiom?  Might we consider factoring these
floating point comparison functions (not the BOOST_CHECK_CLOSE macro,
but the functions it uses) out into a separate library?  Any comments
on my approach?

Any and all thoughts, comments, or complaints welcome.  Thanks!

----------------------------------------------------------------------
Dave Steffen, Ph.D.                Disobey this command!
Software Engineer IV                 - Douglas Hofstadter
Numerica Corporation
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