From: Paul A Bristow (pbristow_at_[hidden])
Date: 2006-02-09 17:19:47
Some of you have noted (with displeasure) the ugly display of floating point
values from
BOOST_CHECK_CLOSE
for example
difference between +1e-6{9.9999999999999995e-007} and
1e-5{1.0000000000000001e-005} exceeds 2.22045e-018%
The number of decimal digits used is enough to show all that can be
significant.
For 64-bit doubles it is 17 decimal digits, (for 32-bit float 9) and for
long double, quad_float even more.
This is undoubtedly ugly, but has the virtue that it avoids apparently
nonsensical displays like
1.000000 != 1.000000
when comparing 1.f, with the next after, one least significant bit above
1.00000012f,
which is what you get if the standard 6 decimal digits for float is used.
It has another great virtue - it highlights the limitations of storing
decimal representations in binary.
There are smarter algorithms for display (which Gennadiy is considering),
but IMO this is the C++ standard way of doing these things and I suggest
that this is the Right Thing To Do in this case.
Are there any dissenting views?
Paul
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