Advanced Rust setup

This document provides basic instructions to configure the Rust toolchain and features for TFHE-rs.

TFHE-rs requires a nightly Rust toolchain to build the C API and utilize advanced SIMD instructions. However, for other uses, a stable toolchain (version 1.81 or later) is sufficient.

Follow the following instructions to install the necessary Rust toolchain:

# If you don't need the C API or the advanced still unstable SIMD instructions use this
rustup toolchain install stable
# Otherwise install a nightly toolchain
rustup toolchain install nightly

Setting the toolchain

You can set the toolchain using either of the following methods.

Manually specify the toolchain for each cargo command:

# By default the +stable should not be needed, but we add it here for completeness
cargo +stable build --release
cargo +stable test --release
# Or
cargo +nightly build --release
cargo +nightly test --release

Override the toolchain for the current project:

# This should not be necessary by default, but if you want to make sure your configuration is
# correct you can still set the overridden toolchain to stable
rustup override set stable
# cargo will use the `stable` toolchain.
cargo build --release
# Or
rustup override set nightly
# cargo will use the `nightly` toolchain.
cargo build --release

To verify the default toolchain used by Cargo, execute:

rustup show

Choosing your features

TFHE-rs provides various cargo features to customize the types and features used.

Homomorphic types

This crate provides 4 kinds of data types. Each kind is enabled by activating the corresponding feature in the TOML line and has multiple types:

Kind	Features	Type (s)
Booleans	boolean	Booleans
ShortInts	shortint	Short integers
Integers	integer	Arbitrary-sized integers
Integers+	extended-types	Non-standard sized integers
Strings	strings	ASCII strings

The Integers+ kind refers to types which have non-standard bit-width like FheUint24 for example. Having more granular types can allow to improve performance. The feature is not enabled by default to avoid very long compile times if users don't need the extended-types.

AVX-512

While the library generally selects automatically the best instruction sets available by the host, in the case of 'AVX-512', you have to choose it explicitly. This requires to use a nightly toolchain with the feature nightly-avx512.

cargo +nightly build --release --features=nightly-avx512