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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | 3x 125x 123x 123x 123x 123x 123x 123x 8x 115x 123x | /**
* Round `value` to `dp` decimal places using decimal half-even (round half to
* even / banker's rounding) so it mirrors the server's `Decimal(round(x, n))`.
*
* This intentionally matches Python's *decimal* half-even behaviour, NOT Python
* float `round()` (e.g. `roundHalfEven(2.675, 2) === 2.68`, whereas float
* `round(2.675, 2)` yields 2.67).
*
* Targeted at the money domain: small magnitudes and `dp <= 3`. The `EPS`
* half-detection tolerance is tuned for that domain and is not intended for
* arbitrary large magnitudes or high precision.
*/
export function roundHalfEven(value: number, dp: number): number {
if (!isFinite(value)) return value;
const factor = Math.pow(10, dp);
const scaled = value * factor;
const floor = Math.floor(scaled);
const diff = scaled - floor;
const EPS = 1e-9;
let rounded: number;
if (Math.abs(diff - 0.5) < EPS) {
rounded = floor % 2 === 0 ? floor : floor + 1;
} else {
rounded = Math.round(scaled);
}
return rounded / factor;
}
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