[Taler] Possible rounding bug in wallet?

[Florian Jung]

Hi,

I have an exchange configured with zero fees:

       for i in `seq 2022 2100`; do
               taler-exchange-offline wire-fee $i iban MANA:0 MANA:0 | taler-exchange-offline upload
               taler-exchange-offline global-fee $i MANA:0 MANA:0 MANA:0 365d 365d 100 | taler-exchange-offline upl
oad
       done

my coins exist in denominations of 100, 10, 1, 0.1, 0.01, and have zero fees configured.

When I use the Android app to withdraw an amount of 13.37 MANA, it shows me the following screen:

Withdraw: 13.36 MANA

Selected amount: 13.36999999 MANA

Fees: -0.00999999 MANA

To me, this smells badly like a floating-point rounding issue. I might have provoked this with my rather wide-spaced coin denominations, but still, this shouldn't happen. (floating point numbers shouldn't be used for monetary amounts in general)

Can you confirm this as a bug, or is there something weird in my setup?

Cheers,

Florian

PS: you can try my deployment using `podman-compose` (like docker, but without docker). It's available online at https://github.com/Windfisch/taler-podman; the commit i tested this issue with is a55f34fdc4d0ca91bd9f8524aeafe3989255278c