FA-61908 / Currency rounding and FX conversion / Member archive

Customer-facing FX amounts use nearest rounding instead of house-favourable rounding · case 03

Receivable amounts are rounded up to the nearest cent, paying customers fractions the dealer does not hold.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

solve(side, amount, ccy, pair, bid, ask): pair is six letters BASEQUOTE; side is the customer's action on the base currency ('buy' or 'sell'). The dealer sells base at ask and buys at bid. If amount is in base, the counter amount in quote is amount*rate; if in quote, the counter amount in base is amount/rate. Amounts the customer pays are rounded up (ceiling) and amounts the customer receives are rounded down (floor) at the counter currency exponent (JPY 0, KWD 3, else 2). Return [counter_amount, counter_ccy]; errors: 'ERR:side', 'ERR:crossed-quote' when bid > ask (bid == ask is valid), 'ERR:currency-not-in-pair'.

Why this case matters

Currency amounts must be rounded at the right stage and in the right unit, or ledgers, quotes and settlements drift by minor units.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression house-rounding-direction 1	`["1658.31", "EUR"]`	`["1658.32", "EUR"]`	Failed

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