C++ User Literal for amrex::Real (_rt) #577
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This adds a user literal for `amrex::Real`. This is a C++11 feature and allows to type constants properly instead of relying on implicit conversation. A typical fallacy is the following user code: ```C++ auto const mypi = 3.14; Real const sphere_volume = 4/3 * mypi * pow(r,3); ``` The first term `4/3` makes the whole expression an `int` until the result is casted to `amrex::Real`. Urgh! We can do better, with `amrex::Real(4)/::amrex:Real(3)` but who wants to write such verbose code, right? So C++11 user literals to the rescue! ```C++ auto const mypi = 3.14_rt; // that's a real, too! Real const sphere_volume 4_rt / 3_rt * mypi * pow(r,3); ```
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ax3l
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Sep 26, 2019
| @@ -769,7 +769,7 @@ FABio_8bit::write (std::ostream& os, | |||
| { | |||
| BL_ASSERT(comp >= 0 && num_comp >= 1 && (comp+num_comp) <= f.nComp()); | |||
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| const Real eps = Real(1.0e-8); // FIXME - whats a better value? | |||
| const Real eps = 1.0e-8_rt; // FIXME - whats a better value? | |||
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Btw, a better value might be std::numeric_limits<Real>::epsilon, without checking what this function actually does.
atmyers
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Sep 26, 2019
This was referenced Sep 26, 2019
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This adds a user literal for
amrex::Real. This is a C++11 feature and allows to type constants properly instead of relying on implicit conversation.A typical fallacy is the following user code:
The first term
4/3makes the whole expression anintuntil the result is casted toamrex::Real. Urgh,4/3 == 1!We can do better, with
amrex::Real(4) / amrex::Real(3)but who wants to write such verbose code, right? Or4./3.which is always adoubleoperation? No. So C++11 user literals to the rescue!Note: the naming
rtis borrowed from the Fortran equivalent usage in AMReX.