fermat-core

128-bit fixed-point decimal arithmetic for Solana's sBPF runtime.

Design Goals

• no_std: Works on Solana sBPF without any OS dependencies.
• Zero external dependencies: Only proptest appears as a dev-dependency.
• Panic-free: Every fallible operation returns Result<_, ArithmeticError>.
• #![forbid(unsafe_code)]: No unsafe blocks anywhere in the crate.
• Overflow-safe mul_div: Uses a 256-bit intermediate (U256) to prevent the class of bugs where (a × b) / c silently wraps when a × b overflows i128.

Core Type

Decimal { mantissa: i128, scale: u8 }
value = mantissa × 10^(-scale)

The scale is bounded to [0, 28] (MAX_SCALE). On-chain Borsh encoding is exactly 17 bytes (16 bytes mantissa LE + 1 byte scale).

Quick Start

use fermat_core::{Decimal, RoundingMode};

let price  = Decimal::new(150_000_000, 6).unwrap(); // 150.000000
let amount = Decimal::new(2_500_000,   6).unwrap(); //   2.500000
let total  = price.checked_mul(amount).unwrap();    // 375.000000...
let result = total.round(6, RoundingMode::HalfEven).unwrap();