nautechsystems/nautilus_trader · error

quantity for {currency} loses precision when decreasing raw

Error message

quantity for {currency} loses precision when decreasing raw scale

What it means

When the quantity's source precision is higher than the target precision, the raw value must be divided down by 10^(source-target). If the raw value is not exactly divisible, the conversion would lose precision, so ensure! raises this error rather than truncating silently — preserving exact discrete values.

Source

Thrown at crates/portfolio/src/manager.rs:1432

fn wallet_money_from_quantity(quantity: Quantity, currency: Currency) -> anyhow::Result<Money> {
    anyhow::ensure!(!quantity.is_undefined(), "quantity was undefined");
    Quantity::from_raw_checked(quantity.raw, quantity.precision)?;
    check_fixed_raw_u128(u128::from(quantity.raw), quantity.precision)?;

    let source_precision = quantity.precision.max(FIXED_PRECISION);
    let target_precision = currency.precision.max(FIXED_PRECISION);
    let raw = i128::try_from(u128::from(quantity.raw))
        .map_err(|_| anyhow::anyhow!("quantity for {currency} exceeds signed raw bounds"))?;
    let raw = match source_precision.cmp(&target_precision) {
        Ordering::Less => {
            let scale = 10_i128.pow(u32::from(target_precision - source_precision));
            raw.checked_mul(scale).ok_or_else(|| {
                anyhow::anyhow!("quantity for {currency} overflowed while increasing raw scale")
            })?
        }
        Ordering::Greater => {
            let scale = 10_i128.pow(u32::from(source_precision - target_precision));
            anyhow::ensure!(
                raw % scale == 0,
                "quantity for {currency} loses precision when decreasing raw scale"
            );
            raw / scale
        }
        Ordering::Equal => raw,
    };
    check_fixed_raw_i128(raw, currency.precision)?;
    let raw: MoneyRaw = raw
        .try_into()
        .map_err(|_| anyhow::anyhow!("quantity for {currency} exceeds Money raw bounds"))?;

    Money::from_raw_checked(raw, currency).map_err(Into::into)
}

fn reservation_precisions_match(
    account: &dyn Account,
    reservations: &AHashMap<Currency, Money>,

View on GitHub (pinned to 18893faf8b)

Solutions

1. Round/quantize the quantity to the currency precision before calling the wallet update
2. Align the currency's precision configuration with the instrument quote precision
3. Use the instrument's size/price precision when constructing Quantity values
4. If truncation is acceptable for your use case, explicitly round before the call instead of relying on the manager

Example fix

// before
let qty = Quantity::new(0.123456789, 9); // currency precision 2
manager.update_balance_locked_wallet(&instrument.id(), asset, qty)?;
// after
let qty = Quantity::new(qty.as_f64(), currency.precision.max(FIXED_PRECISION)); // pre-rounded
manager.update_balance_locked_wallet(&instrument.id(), asset, qty)?;

let target_p = currency.precision.max(FIXED_PRECISION);
if quantity.precision > target_p {
    let scale = 10_u64.pow((quantity.precision - target_p) as u32);
    anyhow::ensure!(quantity.raw % scale == 0, "quantity {} not representable at precision {target_p}", quantity);
}

manager.update_balance_locked_wallet(&id, currency, quantity)
    .unwrap_or_else(|e| { warn!("precision loss for {currency}: {e}; rounding quantity"); });

When it happens

Trigger: Converting a Quantity with more decimal places than the target currency's (or FIXED) precision, where the raw value has non-zero digits in the dropped positions — e.g. quantity precision 8 converted to currency precision 2 with raw not a multiple of 10^6.

Common situations: Trading instruments quoted with more precision than the settlement currency supports; misconfigured currency precision; adapters reporting fills with extra precision beyond the instrument's spec.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

• quantity for {currency} exceeds signed raw bounds
• quantity for {currency} overflowed while increasing raw scal
• Instrument not found in cache: {symbol}
• List of Positions is empty
• value rounded to zero for quantity

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/a3bc1a77d748c35e. Report an issue: GitHub.