...one of the most highly
regarded and expertly designed C++ library projects in the
world.

— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards

It may appear that floating-point numbers are displayed by the *Unit
Test Framework* with an excessive number of decimal digits. However
the number of digits shown is chosen to avoid apparently nonsensical displays
like ```
[1.00000
!= 1.00000]
```

when comparing exactly unity against a
value which is increased by just one least significant binary digit using
the default precision for float of just 6 decimal digits, given by `std::numeric_limits<float>::digits10`

. The function used for the number
of decimal digits displayed is that proposed for a future C++ Standard,
A
Proposal to add a max significant decimal digits value, to be called
`std::numeric_limits::max_digits10();`

.
For 32-bit floats, 9 decimal digits are needed to ensure a single bit change
produces a different decimal digit string.

So a much more helpful display using 9 decimal digits is thus: `[1.00000000 != 1.00000012]`

showing that the two values are in fact
different.

For **IEEE754** 32-bit float values - 9 decimal
digits are shown. For 64-bit **IEEE754** double
- 17 decimal digits. For **IEEE754** extended
long double using 80-bit - 21 decimal digits. For **IEEE754**
quadruple long double 128-bit, and SPARC extended long double 128-bit -
36 decimal digits. For floating-point types, a convenient formula to calculate
`max_digits10`

is: ```
2 + std::numeric_limits<FPT>::digits
* 3010/10000
```

;

Note | |
---|---|

Note that a user defined floating point type UDFPT must define |