Add remaining exact SI constants #336
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chiphogg
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release notes: 📏 lib (new units/constants)
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CMake tests are failing; not sure why yet. |
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Turns out, using `IToA` for magnitudes was a little bit sloppy. Magnitude values are always unsigned, which means there are meaningful values that won't fit inside of an `int64_t`. Fortunately, adding all those constants (#336) was a great stress test to expose this. I think the most natural fix would be to add a `UIToA`, which can't handle signed values, but which _can_ handle the "upper half" of `uint64_t` values. This way, we can have `IToA` delegate to `UIToA` for the "integer magnitude" parts of the logic. Why not just get rid of `IToA` altogether? Well, we do need it for printing exponents, which can be negative. Helps #90: this gets the test to pass on #336.
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chiphogg
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Turns out, using `IToA` for magnitudes was a little bit sloppy. Magnitude values are always unsigned, which means there are meaningful values that won't fit inside of an `int64_t`. Fortunately, adding all those constants (#336) was a great stress test to expose this. I think the most natural fix would be to add a `UIToA`, which can't handle signed values, but which _can_ handle the "upper half" of `uint64_t` values. This way, we can have `IToA` delegate to `UIToA` for the "integer magnitude" parts of the logic. Why not just get rid of `IToA` altogether? Well, we do need it for printing exponents, which can be negative. Helps #90: this gets the test to pass on #336.
Answer: we needed #337. All good now. |
All values were taken from [this section] of the wikipedia page on the 2019 revision of the SI. Admittedly, two of them --- `Delta_nu_Cs` and `K_cd` have horribly awkward names. The best I could do for the constant names was `CESIUM_HYPERFINE_TRANSITION_FREQUENCY` and `LUMINOUS_EFFICACY_540_TERAHERTZ`, respectively. That's fine; we expect most users to do something like this in their programs: ```cpp constexpr auto K_cd = au::LUMINOUS_EFFICACY_540_TERAHERTZ; ``` [this section]: https://en.wikipedia.org/wiki/2019_revision_of_the_SI#Defining_constants
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geoffviola
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All values were taken from this section of the wikipedia page on the
2019 revision of the SI.
Admittedly, two of them ---
Delta_nu_CsandK_cd--- have horriblyawkward names. The best I could do for the constant names was
CESIUM_HYPERFINE_TRANSITION_FREQUENCYandLUMINOUS_EFFICACY_540_TERAHERTZ, respectively. That's fine; we expectmost users to do something like this in their programs:
Helps #90.