reproducible, & possibly configurable rounding

[Bradley M. Kuhn]

Josh Berkus wrote at 19:51 (EDT) on Wednesday:
> ???
> Ledger is written in Python

I respond with ??? in response, since Ledger-CLI is written in C++. :)

> Imagine that a particular kind of revenue gets automatically split
> evenly between 4 earmarks.  Then you receive $14.21 in that account.
> How do you split it so that you don't lose a penny?

This is an interesting case that I wasn't even worried about yet, but
it's important to eventually deal with that.

I am not sure if we'd use Ledger-CLI itself to compute this or not.
Maybe we should?

(Ledger-CLI does have features to automatically split transactions.  I
haven't been using them for earmarks and 10% back to the fiscal sponsor
in part because I'd historically avoided Ledger-CLI's automatic
transaction features for reasons that may now be moot).

> - split amount naively, rounding to two decimals (for USD)
> - compare that against the original amount
> - figure out the number of "lost" pennies
> - reassign those pennies to the splits, based on random selection with
> the probability of each penny being assigned to a split as the % of that
> split, with no duplicates.

This algorithm seems right.  We could also keep track of who got the
pennies last time to avoid the randomness.  Although perhaps that's
overkill.

A first step might to be investigate how Ledger-CLI's automated splits
handle this.
-- 
Bradley M. Kuhn, President, Software Freedom Conservancy