At 15:19 2006-02-09, Paul A Bristow wrote:
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.
I don't see where you're getting your # of digits my calculations show that it's around 14 for 64bit floating and around 7 for 32bit numeric_limits<>::digits10 shows 6 for float, 15 for double on vc8
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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