price-handling
Load when comparing, rounding, formatting, or parsing prices, or designing price types.
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Price Handling Patterns
The price type is f64
IEEE 754 double precision. No fixed-point, no decimal types.
Use i64 fixed-point only for a matching engine (bit-exact required), a regulatory audit trail mandating reproducibility, or a settlement system with legal precision requirements. Hybrid: i64 on the execution hot path, f64 for display and analytics.
Never == on prices
use float_cmp::{approx_eq, F64Margin};
pub const PRICE_EPSILON: f64 = 1e-10; // sub-pipette tolerance
pub fn prices_equal(a: f64, b: f64) -> bool {
approx_eq!(f64, a, b, epsilon = PRICE_EPSILON, ulps = 4)
}
pub fn price_gte(a: f64, b: f64) -> bool { a > b || prices_equal(a, b) }
pub fn price_lte(a: f64, b: f64) -> bool { a < b || prices_equal(a, b) }Round only at the boundaries
| Boundary | Rounding |
|---|---|
| Order submission (OrderRequest → broker API) | Round to tick, then validate alignment |
| Display formatting | Round to the symbol's display_decimals |
| Market data ingestion (ticks, bars, quotes) | Never. Preserve full feed precision |
| P&L calculation | Never. Use raw values |
pub fn round_to_tick(price: f64, tick_size: f64) -> f64 {
(price / tick_size).round() * tick_size
}
pub fn validate_tick_alignment(price: f64, tick_size: f64) -> bool {
prices_equal(price, round_to_tick(price, tick_size))
}Order submission order: round to tick, validate alignment (on failure return an error, never re-round), then format for the broker API if it takes a string.
Format with the symbol's precision, never hardcoded decimals (EURUSD 5, AAPL 2, BTC 8):
format!("{:.1$}", price, symbol.display_decimals as usize)Symbol metadata owns precision
Tick size and display precision belong to the symbol, not to the price value. A Price { value, decimals } struct is the wrong shape.
#[derive(Clone, Copy)]
pub struct SymbolSpec {
pub symbol_id: u32,
pub tick_size: f64, // minimum price increment
pub display_decimals: u8, // decimal places for UI
pub lot_size: f64, // minimum quantity
}
impl SymbolSpec {
pub fn round_price(&self, price: f64) -> f64 {
round_to_tick(price, self.tick_size)
}
pub fn format_price(&self, price: f64) -> String {
format!("{:.1$}", price, self.display_decimals as usize)
}
}The symbol table loads at subscription setup (cold path), is keyed by symbol ID, and re-syncs on reconnect or symbol list change.
Price newtype
Optional: wrap f64 in a #[repr(transparent)] newtype with PartialOrd but no PartialEq; equality goes through prices_equal. Constructor debug_assert!s is_finite(). Use for order types; skip on the market-data hot path.
Normalize feeds to f64 at ingest
Convert at the entry boundary; downstream code sees plain f64 regardless of feed source.
// doubles (IB, dxFeed, Rithmic): pass through
fn ingest_double(value: f64) -> f64 { value }
// strings (Binance, Coinbase): parse
fn ingest_string(s: &str) -> Result<f64, ParseFloatError> { s.parse() }
// scaled integers (CME MDP): unscale
fn ingest_scaled(mantissa: i64, exponent: i8) -> f64 {
mantissa as f64 * 10f64.powi(exponent as i32)
}- Repository
vanillagreencom/kendex
- Revision
32d7bc7
- Last updated
- First committed
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