fermat-core

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

fermat-core is the core arithmetic crate of the fermat-math project. It provides a Decimal type backed by an i128 mantissa and u8 scale, with checked arithmetic, 7 IEEE 754-2008 rounding modes, and a 256-bit intermediate for overflow-safe mul_div.

Features

• #![no_std] — compiles to bare-metal sBPF
• #![forbid(unsafe_code)] — no unsafe blocks anywhere
• Zero external dependencies — minimal binary size
• Every operation returns Result — no panics, ever
• 7 IEEE 754-2008 rounding modes — explicit rounding direction
• checked_mul_div — 256-bit intermediate prevents (a*b)/c overflow
• 17 bytes on-chain — compact i128 + u8 Borsh encoding

Quick Start

use fermat_core::{Decimal, RoundingMode};

let price  = Decimal::new(150_000_000, 6)?;   // 150.000000
let amount = Decimal::new(2_500_000, 6)?;      //   2.500000

let total  = price.checked_mul(amount)?;
let result = total.round(6, RoundingMode::HalfEven)?;  // 375.000000

// Overflow-safe: (a * b) / c via U256 intermediate
let health = collateral.checked_mul_div(threshold, debt)?;

Installation

[dependencies]
fermat-core = "0.1"

Modules

See Also

• fermat-solana — Borsh + SPL token integration
• GitHub — full repository with benchmarks and lending example
• fermatmath.net — project website

License

Licensed under either MIT or Apache-2.0 at your option.

Copyright 2026 XXIX Labs