Calculations are often written in C++, the rounding of which must be controlled. The method _controlfp is usually used for this (https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/control87-controlfp-control87-2?view=msvc-170).
However, due to cross-platform, such a solution in C# is not available. You can work around this limitation by doing a calculation that, according to the IEEE-754 standard, will round to the nearest neighbor, and then manually rounding the result up or down as needed.
In C++ there is a group of methods called std::nextafter and std::nexttoward (https://en.cppreference.com/w/cpp/numeric/math/nextafter).
There is no such thing in .Net Framework. So I decided to write a utility that will allow you to do this. I use this utility in my scientific work because I study interval analysis and I need to use outward rounding in calculations.
The utility guarantees the following behavior:
| Source value | Previous | Next |
|---|---|---|
NaN |
NaN |
NaN |
+Inf |
+Inf |
+Inf |
-Inf |
-Inf |
-Inf |
double.MaxValue |
<prev_number> |
+Inf |
float.MaxValue |
<prev_number> |
+Inf |
double.MinValue |
-Inf |
<next_number> |
float.MinValue |
-Inf |
<next_number> |
0f |
-float.Epsilon |
float.Epsilon |
0d |
-double.Epsilon |
double.Epsilon |
<number> |
<prev_number> |
<next_number> |
It is also guaranteed that between the original number and the result of the utility's calculations there are no other numbers representable in floating point arithmetic. The behavior described above is guaranteed as described in the utility tests.