I used `int` before, because it was simple, and I thought _surely_ it
would be enough. I mean, who's going to make a unit whose magnitude has
a prime factor bigger than 32 bits?
This brings us to the "Dalton", a unit whose ratio-magnitude numerator
is 16605390666050. The prime factorization of 16605390666050 is
(2 * 5 * 5 * 53 * 6266185157), and this last number is bigger than 2^31
by a factor of 3 or so.
Fortunately, we should have done this from the beginning anyway, because
otherwise there would be numbers we could represent in `ratio` which we
couldn't represent in `Magnitude`, and this should never be the case.
```
test\unit_test\runtime\magnitude_test.cpp(143): error C2672:
'units::check_same_type_and_value': no matching overloaded function
found
```
Maybe it's confused by accessing the static member variable template
using dot-notation on an _instance_? If so, let's see how it likes the
member-function syntax.
For each Magnitude `m`, we now support:
- `is_rational(m)` tells whether it represents a rational number.
- `is_integral(m)` tells whether it represents an integer (and
`is_integral(m)` implies `is_rational(m)`).
- `m.value<T>` represents the value of `m` in the type `T`.
If `T` is integral, we only support `m.value<T>` when `is_integral(m)`.
We also perform all intermediate computations in the widest type of the
same category (floating point, signed, or unsigned). This means we can,
for example, give first-class support to embedded users who may have
hardware support only for `float`: we can ensure they get the most
accurate `float` value we can compute, without burdening them with a
dependency on `long double` in their runtime code.
We are not yet ready to replace `ratio` as the definition of unit
magnitudes, but we're a step closer. The next step will be to decompose
a Magnitude into numerator, denominator, and irrational parts, giving us
full bidirectional convertibility with existing `ratio` instances. Then
we can migrate over in a controlled fashion.
The motivation for the `mag` sub-namespace was to distinguish something
like `mag::product_t<...>` from `dim::product_t<...>`, based on the
idioms of Aurora Units. However, we have no need for a `product_t` type
trait, since we can just use `operator*()`, so we can eliminate this
sub-namespace.
The new test actually passed without modifying the code. However, that
might be implementation-dependent (presumably based on canonicalization
of the `ratio` template parameter), so I wanted a more obviously correct
implementation.
Chip Hogg
Mateusz Pusz
Markus Hofbauer