Test against a reference IEEE754 decimal implementation

[anzdaddy]

I created https://github.com/anz-bank/decimal-reference. You can invoke it from the command line (supports cmdline args and stdin input modes) driving arbitrary operations using an RPN notation. The major caveat is that I based it on libdfp, which only wants to compile on Linux, so you need docker to run it.

It still needs to be hooked in for testing purposes, and if we can replace libdfp with a macOS-friendly library to avoid the Docker dependency, that would be awesome (though then we'd have to ensure some kind of build environment, probably Xcode, which has its own challenges).

Either way, we should stick to the cmdline/stdin approach to keep the moving parts fully decoupled.

[anzdaddy]

The other repo is very small. I'm happy to have the content folded into this repo if that's easier.

[juliaogris]

Docker is fine, @joshcarp is on a linux laptop anyway...

[anzdaddy]

Docker is fine, @joshcarp is on a linux laptop anyway...

Cool!

[anzdaddy]

One final thought before I get back to my day job: one option to consider is restricting reference-implementation testing to Linux builds, under the assumption that Go semantics won't change across platforms. Not as complete, but might be good enough if Docker is too hard to integrate into CI on every platform.