nautilus_model/defi/data/

swap_trade_info.rs

// -------------------------------------------------------------------------------------------------
//  Copyright (C) 2015-2026 Nautech Systems Pty Ltd. All rights reserved.
//  https://nautechsystems.io
//
//  Licensed under the GNU Lesser General Public License Version 3.0 (the "License");
//  You may not use this file except in compliance with the License.
//  You may obtain a copy of the License at https://www.gnu.org/licenses/lgpl-3.0.en.html
//
//  Unless required by applicable law or agreed to in writing, software
//  distributed under the License is distributed on an "AS IS" BASIS,
//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//  See the License for the specific language governing permissions and
//  limitations under the License.
// -------------------------------------------------------------------------------------------------

use alloy_primitives::{U160, U256};
use rust_decimal::prelude::ToPrimitive;
use rust_decimal_macros::dec;

use crate::{
    defi::{
        Token,
        data::swap::RawSwapData,
        tick_map::{
            full_math::{DECIMAL_EXPONENT_MAX, FullMath},
            sqrt_price_math::{decode_sqrt_price_x96_to_price_tokens_adjusted, price_from_u256},
        },
    },
    enums::OrderSide,
    types::{Price, Quantity, fixed::FIXED_PRECISION},
};

/// Trade information derived from raw swap data, normalized to market conventions.
///
/// This structure represents a Uniswap V3 swap translated into standard trading terminology
/// (base/quote, buy/sell) for consistency with traditional financial data systems.
///
/// # Base/Quote Token Convention
///
/// Tokens are assigned base/quote roles based on their priority:
/// - Higher priority token → base (asset being traded)
/// - Lower priority token → quote (pricing currency)
///
/// This may differ from the pool's token0/token1 ordering. When token priority differs
/// from pool ordering, we say the market is "inverted":
/// - NOT inverted: token0=base, token1=quote
/// - Inverted: token0=quote, token1=base
///
/// # Prices
///
/// - `spot_price`: Instantaneous pool price after the swap (from `sqrt_price_x96`)
/// - `execution_price`: Average realized price for this swap (from amount ratio)
///
/// Both prices are in quote/base direction (e.g., USDC per WETH) and adjusted for token decimals.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct SwapTradeInfo {
    /// The direction of the trade from the base token perspective.
    pub order_side: OrderSide,
    /// The absolute quantity of the base token involved in the swap.
    pub quantity_base: Quantity,
    /// The absolute quantity of the quote token involved in the swap.
    pub quantity_quote: Quantity,
    /// The instantaneous pool price after the swap (quote per base).
    pub spot_price: Price,
    /// The average realized execution price for this swap (quote per base).
    pub execution_price: Price,
    /// Whether the base/quote assignment differs from token0/token1 ordering.
    pub is_inverted: bool,
    /// The pool price before that swap executed(optional).
    pub spot_price_before: Option<Price>,
}

impl SwapTradeInfo {
    /// Sets the spot price before the swap for price impact and slippage calculations.
    pub fn set_spot_price_before(&mut self, price: Price) {
        self.spot_price_before = Some(price);
    }

    /// Calculates price impact in basis points (requires token references for decimal adjustment).
    ///
    /// Price impact measures the market movement caused by the swap size,
    /// excluding fees. This is the percentage change in spot price from
    /// before to after the swap.
    ///
    /// # Returns
    /// Price impact in basis points (10000 = 100%), saturating at `u32::MAX`
    ///
    /// # Errors
    ///
    /// Returns an error if the spot price before the swap is not set or is zero.
    pub fn get_price_impact_bps(&self) -> anyhow::Result<u32> {
        if let Some(spot_price_before) = self.spot_price_before {
            Self::check_spot_price_before(spot_price_before, PriceMetric::Impact)?;
            let price_change = self.spot_price - spot_price_before;
            let price_impact =
                (price_change.as_decimal() / spot_price_before.as_decimal()).abs() * dec!(10_000);

            Ok(price_impact.round().to_u32().unwrap_or(u32::MAX))
        } else {
            anyhow::bail!("Cannot calculate price impact, the spot price before is not set");
        }
    }

    /// Calculates slippage in basis points (requires token references for decimal adjustment).
    ///
    /// Slippage includes both price impact and fees, representing the total
    /// deviation from the spot price before the swap. This measures the total
    /// cost to the trader.
    ///
    /// # Returns
    /// Total slippage in basis points (10000 = 100%), saturating at `u32::MAX`
    ///
    /// # Errors
    ///
    /// Returns an error if the spot price before the swap is not set or is zero.
    pub fn get_slippage_bps(&self) -> anyhow::Result<u32> {
        if let Some(spot_price_before) = self.spot_price_before {
            Self::check_spot_price_before(spot_price_before, PriceMetric::Slippage)?;
            let price_change = self.execution_price - spot_price_before;
            let slippage =
                (price_change.as_decimal() / spot_price_before.as_decimal()).abs() * dec!(10_000);

            Ok(slippage.round().to_u32().unwrap_or(u32::MAX))
        } else {
            anyhow::bail!("Cannot calculate slippage, the spot price before is not set")
        }
    }

    fn check_spot_price_before(
        spot_price_before: Price,
        metric: PriceMetric,
    ) -> anyhow::Result<()> {
        let metric = metric.name();
        anyhow::ensure!(
            !spot_price_before.is_zero(),
            "Cannot calculate {metric}, the spot price before is zero"
        );
        Ok(())
    }
}

enum PriceMetric {
    Impact,
    Slippage,
}

impl PriceMetric {
    const fn name(self) -> &'static str {
        match self {
            Self::Impact => "price impact",
            Self::Slippage => "slippage",
        }
    }
}

/// Computation engine for deriving market-oriented trade info from raw swap data.
///
/// This calculator translates DEX's token0/token1 representation into standard
/// trading terminology (base/quote, buy/sell) based on token priority.
///
/// # Token Priority and Inversion
///
/// The calculator determines which token is base vs quote by comparing token priorities.
/// When the higher-priority token is token1 (not token0), the market is "inverted":
///
/// # Precision Handling
///
/// Quantities keep each token's decimals and return an error when those exceed the
/// supported quantity precision. Prices always use `FIXED_PRECISION`.
#[derive(Debug)]
pub struct SwapTradeInfoCalculator<'a> {
    /// Reference to token0 from the pool.
    token0: &'a Token,
    /// Reference to token1 from the pool.
    token1: &'a Token,
    /// Whether the base/quote assignment differs from token0/token1 ordering.
    ///
    /// - `true`: token0=quote, token1=base (inverted)
    /// - `false`: token0=base, token1=quote (normal)
    pub is_inverted: bool,
    /// Raw swap amounts and resulting sqrt price from the blockchain event.
    raw_swap_data: RawSwapData,
}

impl<'a> SwapTradeInfoCalculator<'a> {
    #[must_use]
    pub fn new(token0: &'a Token, token1: &'a Token, raw_swap_data: RawSwapData) -> Self {
        let is_inverted = token0.get_token_priority() < token1.get_token_priority();
        Self {
            token0,
            token1,
            is_inverted,
            raw_swap_data,
        }
    }

    /// Determines swap direction from amount signs.
    ///
    /// Returns `true` if swapping token0 for token1 (`zero_for_one`).
    #[must_use]
    pub fn zero_for_one(&self) -> bool {
        self.raw_swap_data.amount0.is_positive()
    }

    /// Computes all trade information fields and returns a complete [`SwapTradeInfo`].
    ///
    /// Calculates order side, quantities, and prices from the raw swap data,
    /// applying token priority rules and decimal adjustments. If the price before
    /// the swap is provided, also computes price impact and slippage metrics.
    ///
    /// # Arguments
    ///
    /// * `sqrt_price_x96_before` - Optional square root price before the swap (Q96 format).
    ///   When provided, enables calculation of `spot_price_before`, price impact, and slippage.
    ///
    /// # Errors
    ///
    /// Returns an error if:
    /// - A token decimal count exceeds `DECIMAL_EXPONENT_MAX` (77).
    /// - A quantity or price calculation fails.
    pub fn compute(&self, sqrt_price_x96_before: Option<U160>) -> anyhow::Result<SwapTradeInfo> {
        let spot_price_before = if let Some(sqrt_price_x96_before) = sqrt_price_x96_before {
            Some(decode_sqrt_price_x96_to_price_tokens_adjusted(
                sqrt_price_x96_before,
                self.token0.decimals,
                self.token1.decimals,
                self.is_inverted,
            )?)
        } else {
            None
        };

        Ok(SwapTradeInfo {
            order_side: self.order_side(),
            quantity_base: self.quantity_base()?,
            quantity_quote: self.quantity_quote()?,
            spot_price: self.spot_price()?,
            execution_price: self.execution_price()?,
            is_inverted: self.is_inverted,
            spot_price_before,
        })
    }

    /// Determines the order side from the perspective of the determined base/quote tokens.
    ///
    /// Uses market convention where base is the asset being traded and quote is the pricing currency.
    ///
    /// # Returns
    /// - `OrderSide::Buy` when buying base token (selling quote for base)
    /// - `OrderSide::Sell` when selling base token (buying quote with base)
    ///
    /// # Logic
    ///
    /// The order side depends on:
    /// 1. Which token is being bought/sold (from amount signs)
    /// 2. Which token is base vs quote (from priority determination)
    #[must_use]
    pub fn order_side(&self) -> OrderSide {
        let zero_for_one = self.zero_for_one();

        if self.is_inverted {
            // When inverted: token0=quote, token1=base
            // - zero_for_one (sell token0/quote, buy token1/base) -> BUY base
            // - one_for_zero (sell token1/base, buy token0/quote -> SELL base
            if zero_for_one {
                OrderSide::Buy
            } else {
                OrderSide::Sell
            }
        } else {
            // When NOT inverted: token0=base, token1=quote
            // - zero_for_one (sell token0/base, buy token1/quote) → SELL base
            // - one_for_zero (sell token1/quote, buy token0/base) → BUY base
            if zero_for_one {
                OrderSide::Sell
            } else {
                OrderSide::Buy
            }
        }
    }

    /// Returns the quantity of the base token involved in the swap.
    ///
    /// This is always the amount of the base asset being traded,
    /// regardless of whether it's token0 or token1 in the pool.
    ///
    /// # Returns
    /// Absolute value of base token amount with proper decimals
    ///
    /// # Errors
    ///
    /// Returns an error if the amount cannot be converted to a valid `Quantity`.
    pub fn quantity_base(&self) -> anyhow::Result<Quantity> {
        let (amount, precision) = if self.is_inverted {
            (
                self.raw_swap_data.amount1.unsigned_abs(),
                self.token1.decimals,
            )
        } else {
            (
                self.raw_swap_data.amount0.unsigned_abs(),
                self.token0.decimals,
            )
        };

        Quantity::from_u256(amount, precision).map_err(Into::into)
    }

    /// Returns the quantity of the quote token involved in the swap.
    ///
    /// This is always the amount of the quote (pricing) currency,
    /// regardless of whether it's token0 or token1 in the pool.
    ///
    /// # Returns
    /// Absolute value of quote token amount with proper decimals
    ///
    /// # Errors
    ///
    /// Returns an error if the amount cannot be converted to a valid `Quantity`.
    pub fn quantity_quote(&self) -> anyhow::Result<Quantity> {
        let (amount, precision) = if self.is_inverted {
            (
                self.raw_swap_data.amount0.unsigned_abs(),
                self.token0.decimals,
            )
        } else {
            (
                self.raw_swap_data.amount1.unsigned_abs(),
                self.token1.decimals,
            )
        };

        Quantity::from_u256(amount, precision).map_err(Into::into)
    }

    /// Returns the human-readable spot price in base/quote (market) convention.
    ///
    /// This is the instantaneous market price after the swap, adjusted for token decimals
    /// to provide a human-readable value. This price does NOT include fees or slippage.
    ///
    /// # Returns
    /// Price adjusted for token decimals in quote/base direction (market convention).
    ///
    /// # Base/Quote Logic
    /// - When `is_inverted=false`: token0=base, token1=quote → returns token1/token0 (quote/base)
    /// - When `is_inverted=true`: token0=quote, token1=base → returns token0/token1 (quote/base)
    ///
    /// # Use Cases
    /// - Displaying current market price to users
    /// - Calculating price impact: `(spot_after - spot_before) / spot_before`
    /// - Comparing market rate vs execution rate
    /// - Real-time price feeds
    fn spot_price(&self) -> anyhow::Result<Price> {
        // Pool always stores token1/token0
        // When is_inverted=false: token0=base, token1=quote → want token1/token0 (quote/base) → don't invert
        // When is_inverted=true: token0=quote, token1=base → want token0/token1 (quote/base) → invert
        decode_sqrt_price_x96_to_price_tokens_adjusted(
            self.raw_swap_data.sqrt_price_x96,
            self.token0.decimals,
            self.token1.decimals,
            self.is_inverted, // invert when base/quote differs from token0/token1
        )
    }

    /// Calculates the average execution price for this swap (includes fees and slippage).
    ///
    /// This is the actual realized price paid/received in the swap, calculated from
    /// the input and output amounts. This represents the true cost of the trade.
    ///
    /// # Returns
    /// Price in quote/base direction (market convention), adjusted for token decimals.
    ///
    /// # Formula
    /// ```text
    /// price = (quote_amount / 10^quote_decimals) / (base_amount / 10^base_decimals)
    ///       = (quote_amount * 10^base_decimals) / (base_amount * 10^quote_decimals)
    /// ```
    ///
    /// To preserve precision in U256 arithmetic, we scale by `10^FIXED_PRECISION`:
    /// ```text
    /// price_raw = (quote_amount * 10^base_decimals * 10^FIXED_PRECISION) / (base_amount * 10^quote_decimals)
    /// ```
    ///
    /// # Base/Quote Logic
    /// - When `is_inverted=false`: quote=token1, base=token0 → price = amount1/amount0
    /// - When `is_inverted=true`: quote=token0, base=token1 → price = amount0/amount1
    ///
    /// # Use Cases
    /// - Trade accounting and P&L calculation
    /// - Comparing quoted vs executed prices
    /// - Cost analysis (includes all fees and price impact)
    /// - Performance reporting
    fn execution_price(&self) -> anyhow::Result<Price> {
        let amount0 = self.raw_swap_data.amount0.unsigned_abs();
        let amount1 = self.raw_swap_data.amount1.unsigned_abs();

        if amount0.is_zero() || amount1.is_zero() {
            anyhow::bail!("Cannot calculate execution price with zero amounts");
        }

        // Determine base and quote amounts/decimals based on inversion
        let (quote_amount, base_amount, quote_decimals, base_decimals) = if self.is_inverted {
            // inverted: token0=quote, token1=base
            (amount0, amount1, self.token0.decimals, self.token1.decimals)
        } else {
            // not inverted: token0=base, token1=quote
            (amount1, amount0, self.token1.decimals, self.token0.decimals)
        };

        FullMath::check_decimal_exponent(base_decimals)?;
        FullMath::check_decimal_exponent(quote_decimals)?;

        let exponent =
            i16::from(base_decimals) + i16::from(FIXED_PRECISION) - i16::from(quote_decimals);
        let price_raw_u256 = if exponent >= 0 {
            let exponent = u8::try_from(exponent)
                .map_err(|_| anyhow::anyhow!("Decimal exponent {exponent} exceeds u8 range"))?;
            let primary_exponent = exponent.min(DECIMAL_EXPONENT_MAX);
            let secondary_exponent = exponent - primary_exponent;
            let primary_scalar = FullMath::pow10(primary_exponent)?;
            let secondary_scalar = FullMath::pow10(secondary_exponent)?;
            FullMath::mul_div_scaled(
                quote_amount,
                U256::from(1),
                base_amount,
                &[primary_scalar, secondary_scalar],
            )?
        } else {
            let divisor_exponent = u8::try_from(exponent.unsigned_abs())
                .map_err(|_| anyhow::anyhow!("Decimal exponent {exponent} exceeds u8 range"))?;
            let divisor = FullMath::pow10(divisor_exponent)?;
            (quote_amount / base_amount) / divisor
        };

        price_from_u256(price_raw_u256)
    }
}

#[cfg(test)]
mod tests {
    use std::str::FromStr;

    use alloy_primitives::{I256, U160};
    use rstest::{fixture, rstest};
    use rust_decimal_macros::dec;

    use super::*;
    use crate::defi::{
        stubs::{usdc, weth},
        tick_map::{full_math::Q96_U160, tick_math::MAX_SQRT_RATIO},
    };

    #[fixture]
    fn swap_trade_info() -> SwapTradeInfo {
        SwapTradeInfo {
            order_side: OrderSide::Buy,
            quantity_base: Quantity::from("1"),
            quantity_quote: Quantity::from("2"),
            spot_price: Price::from_raw(2, FIXED_PRECISION),
            execution_price: Price::from_raw(3, FIXED_PRECISION),
            is_inverted: true,
            spot_price_before: Some(Price::from_raw(1, FIXED_PRECISION)),
        }
    }

    #[rstest]
    fn test_get_price_impact_bps_rejects_zero_spot_price_before(
        mut swap_trade_info: SwapTradeInfo,
    ) {
        swap_trade_info.spot_price_before = Some(Price::zero(FIXED_PRECISION));

        let error = swap_trade_info.get_price_impact_bps().unwrap_err();

        assert_eq!(
            error.to_string(),
            "Cannot calculate price impact, the spot price before is zero"
        );
    }

    #[rstest]
    fn test_get_slippage_bps_rejects_zero_spot_price_before(mut swap_trade_info: SwapTradeInfo) {
        swap_trade_info.spot_price_before = Some(Price::zero(FIXED_PRECISION));

        let error = swap_trade_info.get_slippage_bps().unwrap_err();

        assert_eq!(
            error.to_string(),
            "Cannot calculate slippage, the spot price before is zero"
        );
    }

    #[rstest]
    fn test_get_price_impact_bps_accepts_smallest_positive_spot_price_before(
        swap_trade_info: SwapTradeInfo,
    ) {
        assert_eq!(swap_trade_info.get_price_impact_bps().unwrap(), 10_000);
    }

    #[rstest]
    fn test_get_slippage_bps_accepts_smallest_positive_spot_price_before(
        swap_trade_info: SwapTradeInfo,
    ) {
        assert_eq!(swap_trade_info.get_slippage_bps().unwrap(), 20_000);
    }

    #[rstest]
    fn test_get_price_impact_and_slippage_bps_saturate_beyond_u32(
        mut swap_trade_info: SwapTradeInfo,
    ) {
        let one = Price::from_raw(10_i128.pow(u32::from(FIXED_PRECISION)), FIXED_PRECISION);
        swap_trade_info.spot_price = one;
        swap_trade_info.execution_price = one;

        assert_eq!(swap_trade_info.get_price_impact_bps().unwrap(), u32::MAX);
        assert_eq!(swap_trade_info.get_slippage_bps().unwrap(), u32::MAX);
    }

    #[rstest]
    fn test_swap_trade_info_calculator_calculations_buy(weth: Token, usdc: Token) {
        // Real Arbitrum transaction: https://arbiscan.io/tx/0xb9af1fd5eefe82650a5e0f8ff10b3a5e1c7f05f44f255e1335360df97bd1645a
        let raw_data = RawSwapData::new(
            I256::from_str("-466341596920355889").unwrap(),
            I256::from_str("1656236893").unwrap(),
            U160::from_str("4720799958938693700000000").unwrap(),
        );

        let calculator = SwapTradeInfoCalculator::new(&weth, &usdc, raw_data);
        let result = calculator.compute(None).unwrap();
        // Its not inverted first is WETH(base) and second USDC(quote) as stablecoin
        assert!(!calculator.is_inverted);
        // Its buy, as amount0(WETH) < 0 (we received WETH, pool outflow) and amount1 > 0 (USDC sent, pool inflow)
        assert_eq!(result.order_side, OrderSide::Buy);
        assert_eq!(
            result.quantity_base.as_decimal(),
            dec!(0.466341596920355889)
        );
        assert_eq!(result.quantity_quote.as_decimal(), dec!(1656.236893));
        assert_eq!(result.spot_price.as_decimal(), dec!(3550.3570265047994091));
        assert_eq!(
            result.execution_price.as_decimal(),
            dec!(3551.5529902061477063)
        );
    }

    #[rstest]
    fn test_swap_trade_info_calculator_calculations_sell(weth: Token, usdc: Token) {
        //Real Arbitrum transaction: https://arbiscan.io/tx/0x1fbedacf4a1cc7f76174d905c93d2f56d42335cadb4a782e2d74e3019107286b
        let raw_data = RawSwapData::new(
            I256::from_str("193450074461093702").unwrap(),
            I256::from_str("-691892530").unwrap(),
            U160::from_str("4739235524363817533004858").unwrap(),
        );

        let calculator = SwapTradeInfoCalculator::new(&weth, &usdc, raw_data);
        let result = calculator.compute(None).unwrap();
        // Its sell as amount0(WETH) > 0 (we send WETH, pool inflow) and amount1 <0 (USDC received, pool outflow)
        assert_eq!(result.order_side, OrderSide::Sell);
        assert_eq!(
            result.quantity_base.as_decimal(),
            dec!(0.193450074461093702)
        );
        assert_eq!(result.quantity_quote.as_decimal(), dec!(691.89253));
        assert_eq!(result.spot_price.as_decimal(), dec!(3578.1407251651610105));
        assert_eq!(
            result.execution_price.as_decimal(),
            dec!(3576.5947980503469024)
        );
    }

    #[rstest]
    fn test_swap_trade_info_calculator_spot_price_overflow_is_recoverable(
        weth: Token,
        usdc: Token,
    ) {
        // A near-MAX_SQRT_RATIO swap overflows spot-price decoding, so compute must return a
        // recoverable error rather than panic, letting the sync keep the swap with empty metadata.
        let raw_data = RawSwapData::new(
            I256::from_str("1").unwrap(),
            I256::from_str("-1").unwrap(),
            MAX_SQRT_RATIO - U160::from(1),
        );

        let calculator = SwapTradeInfoCalculator::new(&weth, &usdc, raw_data);

        assert!(calculator.compute(None).is_err());
    }

    #[rstest]
    fn test_execution_price_scales_distinct_decimals_in_both_directions(weth: Token, usdc: Token) {
        let normal_data = RawSwapData::new(
            I256::from_str("-2000000000000000000").unwrap(),
            I256::from_str("5000000").unwrap(),
            Q96_U160,
        );
        let inverted_data = RawSwapData::new(
            I256::from_str("5000000").unwrap(),
            I256::from_str("-2000000000000000000").unwrap(),
            Q96_U160,
        );

        let normal = SwapTradeInfoCalculator::new(&weth, &usdc, normal_data)
            .execution_price()
            .unwrap();
        let inverted = SwapTradeInfoCalculator::new(&usdc, &weth, inverted_data)
            .execution_price()
            .unwrap();
        let expected = Price::from_raw(25_000_000_000_000_000, FIXED_PRECISION);

        assert_eq!(normal, expected);
        assert_eq!(inverted, expected);
    }

    #[rstest]
    fn test_execution_price_scales_negative_net_exponent(mut weth: Token, mut usdc: Token) {
        weth.decimals = 0;
        usdc.decimals = 18;
        let raw_data = RawSwapData::new(
            I256::from_str("4").unwrap(),
            I256::from_str("-400").unwrap(),
            Q96_U160,
        );

        let result = SwapTradeInfoCalculator::new(&weth, &usdc, raw_data)
            .execution_price()
            .unwrap();

        assert_eq!(result, Price::from_raw(1, FIXED_PRECISION));
    }

    #[rstest]
    fn test_execution_price_accepts_largest_decimal_exponent(mut weth: Token, mut usdc: Token) {
        weth.decimals = DECIMAL_EXPONENT_MAX;
        usdc.decimals = 0;
        let raw_data = RawSwapData::new(
            I256::from_raw(FullMath::pow10(76).unwrap()),
            I256::from_str("-1").unwrap(),
            Q96_U160,
        );

        let result = SwapTradeInfoCalculator::new(&weth, &usdc, raw_data)
            .execution_price()
            .unwrap();

        assert_eq!(
            result,
            Price::from_raw(100_000_000_000_000_000, FIXED_PRECISION)
        );
    }

    #[rstest]
    fn test_execution_price_rejects_first_unsupported_decimal_exponent(
        mut weth: Token,
        mut usdc: Token,
    ) {
        weth.decimals = DECIMAL_EXPONENT_MAX + 1;
        usdc.decimals = 0;
        let raw_data = RawSwapData::new(
            I256::from_str("1").unwrap(),
            I256::from_str("-1").unwrap(),
            Q96_U160,
        );

        let error = SwapTradeInfoCalculator::new(&weth, &usdc, raw_data)
            .execution_price()
            .unwrap_err();

        assert_eq!(
            error.to_string(),
            "Decimal exponent 78 exceeds supported maximum 77"
        );
    }
}