Num parser performance

[allykzam]

Saw "Optimized Numeric Type Handling" in the todo list in the readme, thought I'd poke around because it was Friday afternoon and I was bored. Adding this PR to give an overview of what I came up with; happy to put a proper PR together later if you want to use either of these implementations.

Minor points of note are marking isnumchar as inline, and replacing the isnegative function with a value; the current code appears to be running isnegative twice, even in an optimized release build.

Major differences in my code is the removal of the StringBuilder and calls to Double.TryParse and Int64.TryParse; I've replaced all that with tracking of the current value as a rational of p and q. After parsing, if no dot was found, p is returned as-is, if a dot was found, p and q are converted to double and divided appropriately. I'm sure there's probably some pros/cons to doing this for fractional values vs just using Double.TryParse.

Generated the timings provided on an i7 3770 in an iMac running Windows 7 inside parallels with 8 logical processors. Each timing was generated by resetting F# Interactive in VS to avoid GC from previous tests, then selecting and running lines 1-15 to get the parser pushed through the JIT, and then separately running the appropriate "speed test" code. YMMV 😬

[Rickasaurus]

Hi @amazingant , I'm sorry I totally missed this until now, thanks for putting some time in. I didn't realize anyone else was hacking on Barb.

By optimized numerics I meant the execution level as Barb only needs to be parsed once but is (at least as I use it) run many times (for each record). This is still interesting work though.

I'd like to see an optimization like this paired with FSCheck as it looks pretty complicated and I'd want to make sure no cases are left out.

I plan on putting much more effort into Barb over the coming months. Please let me know if you're still interested in hacking on it.

[allykzam]

I had a wee bit of fun playing with it; I was working with my own parser at the time based on FParsec, and I really liked the concept of using active patterns as part of the parser logic. :)

I've built up a nice backlog of projects to work on since I worked on this, so I don't know as I'll be able to hack at it much for now. I'll try to check in as I have time, and I'll be sure to let you know if I start poking at something.

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