Question: A simple way to round decimal?

[asv]

Thanks for the library!
Can you please tell me how to round decimal from 4 to 2 decimal places?

For example 1234.4567 -> 1234.46.

[nikolaydubina]

Is this over the wire? If you have JSON number (string) {"stock": 1234.4567}, then this lib with fp3 will discard 7 and keep 1234.456. Similar happens with direct use of ParseFixedPointDecimal. The current implementation of parser disregards all digits after specified number (for fp3 it is 3). If you need more, then need to define new type fp4 or if it is dynamic can reference to https://github.com/nikolaydubina/fpmoney.

If it is already parsed number output of ParseFixedPointDecimal, then you can round with any policy, but have to do yourself, it is not implemented here.

If it is fp3.Decimal and we want to reduce to 2 decimals, there is no function to export internal value yet. But feel free to add! There is reversed function tho FromIntScaled.

Also, if it is (a fp3.Decimal) Round(n int) fp3.Decimal also nice to have!

[asv]

I thought that decimal rounding is a complex computer science problem and should be solved by professionals... ;) But if you tell me which direction to dig, I can try to write a patch.

[nikolaydubina]

haha. yeah let's improve rounding for this pkg! Can be in separate PRs:

1. func (v fp3.Decimal) IntUnscaled() int64 - returns internal raw value without scaling.
2. (a fp3.Decimal) Round(n int) fp3.Decimal - round half up number of decimal points (e.g. 0.5 Round(1) -> 1.0; 0.001 Round(3) -> 0.001)
3. global pkg level var for policy of fp3 pkg parsing + new func ParseFixedPointDecimalWithRounding that uses it. be default original behavior = "discard digits without rounding". This is a bit more complex.

For all of these need fuzz test (with couple unit tests or scenarios).

Thanks for interest! 💪🏻