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Add target u32/u64 backend override
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As suggested in 453 it is sometimes feasible to
select the backend bits via an override.

This change provides an override via `cfg(dalek_bits)`
to override the used serial or fiat target backend.
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pinkforest committed Dec 7, 2022
1 parent 29466f1 commit 2f0ce08
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Showing 7 changed files with 49 additions and 23 deletions.
5 changes: 4 additions & 1 deletion .github/workflows/rust.yml
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Expand Up @@ -115,4 +115,7 @@ jobs:
- uses: actions/checkout@v3
- uses: dtolnay/rust-toolchain@stable
# This filter selects no benchmarks, so we don't run any, only build them.
- run: cargo bench "nonexistentbenchmark"
- name: Build u32 bench
run: env RUSTFLAGS="--cfg dalek_bits=\"32\"" cargo bench "nonexistentbenchmark"
- name: Build u64 bench
run: env RUSTFLAGS="--cfg dalek_bits=\"64\"" cargo bench "nonexistentbenchmark"
1 change: 1 addition & 0 deletions CHANGELOG.md
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Expand Up @@ -5,6 +5,7 @@ major series.

## 4.x series

* Add target u32/u64 backend overrides
* Migrate documentation to docs.rs hosted
* Fix backend documentation generation
* Deprecate `EdwardsPoint::hash_from_bytes` and rename it `EdwardsPoint::nonspect_map_to_curve`
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13 changes: 9 additions & 4 deletions src/backend/serial/mod.rs
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Expand Up @@ -21,18 +21,23 @@
use cfg_if::cfg_if;

cfg_if! {

if #[cfg(feature = "fiat_backend")] {
#[cfg(not(target_pointer_width = "64"))]

#[cfg(dalek_bits = "32")]
pub mod fiat_u32;

#[cfg(target_pointer_width = "64")]
#[cfg(dalek_bits = "64")]
pub mod fiat_u64;

} else {
#[cfg(not(target_pointer_width = "64"))]

#[cfg(dalek_bits = "32")]
pub mod u32;

#[cfg(target_pointer_width = "64")]
#[cfg(dalek_bits = "64")]
pub mod u64;

}
}

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12 changes: 6 additions & 6 deletions src/constants.rs
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Expand Up @@ -38,14 +38,14 @@ use crate::scalar::Scalar;

cfg_if! {
if #[cfg(feature = "fiat_backend")] {
#[cfg(not(target_pointer_width = "64"))]
#[cfg(dalek_bits = "32")]
pub use crate::backend::serial::fiat_u32::constants::*;
#[cfg(target_pointer_width = "64")]
#[cfg(dalek_bits = "64")]
pub use crate::backend::serial::fiat_u64::constants::*;
} else {
#[cfg(not(target_pointer_width = "64"))]
#[cfg(dalek_bits = "32")]
pub use crate::backend::serial::u32::constants::*;
#[cfg(target_pointer_width = "64")]
#[cfg(dalek_bits = "64")]
pub use crate::backend::serial::u64::constants::*;
}
}
Expand Down Expand Up @@ -149,7 +149,7 @@ mod test {

/// Test that d = -121665/121666
#[test]
#[cfg(all(not(target_pointer_width = "64"), not(feature = "fiat_backend")))]
#[cfg(all(dalek_bits = "32", not(feature = "fiat_backend")))]
fn test_d_vs_ratio() {
use crate::backend::serial::u32::field::FieldElement2625;
let a = -&FieldElement2625([121665, 0, 0, 0, 0, 0, 0, 0, 0, 0]);
Expand All @@ -162,7 +162,7 @@ mod test {

/// Test that d = -121665/121666
#[test]
#[cfg(all(target_pointer_width = "64", not(feature = "fiat_backend")))]
#[cfg(all(dalek_bits = "64", not(feature = "fiat_backend")))]
fn test_d_vs_ratio() {
use crate::backend::serial::u64::field::FieldElement51;
let a = -&FieldElement51([121665, 0, 0, 0, 0]);
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10 changes: 5 additions & 5 deletions src/field.rs
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Expand Up @@ -37,9 +37,9 @@ use crate::constants;

cfg_if! {
if #[cfg(feature = "fiat_backend")] {
#[cfg(not(target_pointer_width = "64"))]
#[cfg(dalek_bits = "32")]
pub use backend::serial::fiat_u32::field::*;
#[cfg(target_pointer_width = "64")]
#[cfg(dalek_bits = "64")]
pub use backend::serial::fiat_u64::field::*;

/// A `FieldElement` represents an element of the field
Expand All @@ -49,7 +49,7 @@ cfg_if! {
/// implementations.
///
/// Using formally-verified field arithmetic from fiat-crypto.
#[cfg(not(target_pointer_width = "64"))]
#[cfg(dalek_bits = "32")]
pub type FieldElement = backend::serial::fiat_u32::field::FieldElement2625;

/// A `FieldElement` represents an element of the field
Expand All @@ -59,9 +59,9 @@ cfg_if! {
/// implementations.
///
/// Using formally-verified field arithmetic from fiat-crypto.
#[cfg(target_pointer_width = "64")]
#[cfg(dalek_bits = "64")]
pub type FieldElement = backend::serial::fiat_u64::field::FieldElement51;
} else if #[cfg(target_pointer_width = "64")] {
} else if #[cfg(dalek_bits = "64")] {
pub use crate::backend::serial::u64::field::*;

/// A `FieldElement` represents an element of the field
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17 changes: 17 additions & 0 deletions src/lib.rs
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Expand Up @@ -22,6 +22,23 @@
)]
#![doc(html_root_url = "https://docs.rs/curve25519-dalek/4.0.0-pre.2")]
#![doc = include_str!("../README.md")]
//------------------------------------------------------------------------
// curve25519-dalek arithmetric default and overrides
//------------------------------------------------------------------------
#![cfg_attr(
any(
all(not(target_pointer_width = "64"), not(dalek_bits = "64")),
dalek_bits = "32"
),
cfg(dalek_bits = "32")
)]
#![cfg_attr(
any(
all(target_pointer_width = "64", not(dalek_bits = "32")),
dalek_bits = "64"
),
cfg(dalek_bits = "64")
)]

//------------------------------------------------------------------------
// External dependencies:
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14 changes: 7 additions & 7 deletions src/scalar.rs
Original file line number Diff line number Diff line change
Expand Up @@ -172,36 +172,36 @@ cfg_if! {
///
/// This is a type alias for one of the scalar types in the `backend`
/// module.
#[cfg(not(target_pointer_width = "64"))]
#[cfg(dalek_bits = "32")]
#[cfg_attr(
docsrs,
doc(cfg(all(feature = "fiat_backend", not(target_pointer_width = "64"))))
doc(cfg(all(feature = "fiat_backend", dalek_bits = "32")))
)]
type UnpackedScalar = backend::serial::fiat_u32::scalar::Scalar29;

/// An `UnpackedScalar` represents an element of the field GF(l), optimized for speed.
///
/// This is a type alias for one of the scalar types in the `backend`
/// module.
#[cfg(target_pointer_width = "64")]
#[cfg(dalek_bits = "64")]
#[cfg_attr(
docsrs,
doc(cfg(all(feature = "fiat_backend", target_pointer_width = "64")))
doc(cfg(all(feature = "fiat_backend", dalek_bits = "64")))
)]
type UnpackedScalar = backend::serial::fiat_u64::scalar::Scalar52;
} else if #[cfg(target_pointer_width = "64")] {
} else if #[cfg(dalek_bits = "64")] {
/// An `UnpackedScalar` represents an element of the field GF(l), optimized for speed.
///
/// This is a type alias for one of the scalar types in the `backend`
/// module.
#[cfg_attr(docsrs, doc(cfg(target_pointer_width = "64")))]
#[cfg_attr(docsrs, doc(cfg(dalek_bits = "64")))]
type UnpackedScalar = backend::serial::u64::scalar::Scalar52;
} else {
/// An `UnpackedScalar` represents an element of the field GF(l), optimized for speed.
///
/// This is a type alias for one of the scalar types in the `backend`
/// module.
#[cfg_attr(docsrs, doc(cfg(not(target_pointer_width = "64"))))]
#[cfg_attr(docsrs, doc(cfg(dalek_bits = "64")))]
type UnpackedScalar = backend::serial::u32::scalar::Scalar29;
}
}
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