polyval: rename backend module => field_element

It's now the home of the `FieldElement` struct, and the backends are
backends of our field element implementation.

Additionally renames the following submodules of `field_element`  named
after their CPU instructions to the CPUs those instructions are for:

- `clmul` => `x86`
- `pmull` => `armv8`

Author: tarcieri

polyval/src/backend.rs polyval/src/field_element.rspolyval/src/backend.rs renamed to polyval/src/field_element.rs

@@ -1,4 +1,4 @@
-//! POLYVAL backends
+//! POLYVAL field element implementation.
 
 mod soft;
 
@@ -14,19 +14,19 @@ use zeroize::Zeroize;
 cfg_if! {
     if #[cfg(all(target_arch = "aarch64", not(polyval_backend = "soft")))] {
         mod autodetect;
-        mod pmull;
+        mod armv8;
         mod common;
-        pub use crate::backend::autodetect::Polyval as PolyvalGeneric;
+        pub use autodetect::Polyval as PolyvalGeneric;
     } else if #[cfg(all(
         any(target_arch = "x86_64", target_arch = "x86"),
         not(polyval_backend = "soft")
     ))] {
         mod autodetect;
         mod clmul;
         mod common;
-        pub use crate::backend::autodetect::Polyval as PolyvalGeneric;
+        pub use autodetect::Polyval as PolyvalGeneric;
     } else {
-        pub use crate::backend::soft::Polyval as PolyvalGeneric;
+        pub use soft::Polyval as PolyvalGeneric;
     }
 }
 
@@ -37,7 +37,8 @@ cfg_if! {
 ///
 /// # Representation
 ///
-/// The element is represented as 16-bytes in little-endian order.
+/// The element is represented as 16-bytes in little-endian order, using a `repr(C)` ABI and
+/// 16-byte alignment enforced with `align(16)`.
 ///
 /// Arithmetic in POLYVAL's field has the following properties:
 /// - All arithmetic operations are performed modulo the polynomial above.

polyval/src/backend/pmull.rs polyval/src/field_element/armv8.rspolyval/src/backend/pmull.rs renamed to polyval/src/field_element/armv8.rs

@@ -16,7 +16,7 @@
 #![allow(unsafe_op_in_unsafe_fn)]
 
 use super::FieldElement;
-use crate::{Block, Key, Tag, backend::common};
+use crate::{Block, Key, Tag, field_element::common};
 use core::{arch::aarch64::*, mem, ops::Mul};
 use universal_hash::{
     KeyInit, ParBlocks, Reset, UhfBackend,

polyval/src/backend/autodetect.rs polyval/src/field_element/autodetect.rspolyval/src/backend/autodetect.rs renamed to polyval/src/field_element/autodetect.rs

@@ -1,7 +1,7 @@
 //! Autodetection for CPU intrinsics, with fallback to the "soft" backend when
 //! they are unavailable.
 
-use crate::{Key, Tag, backend::soft};
+use crate::{Key, Tag, field_element::soft};
 use core::mem::ManuallyDrop;
 use universal_hash::{
     KeyInit, Reset, UhfClosure, UniversalHash,
@@ -12,7 +12,7 @@ use universal_hash::{
 };
 
 #[cfg(target_arch = "aarch64")]
-use super::pmull as intrinsics;
+use super::armv8 as intrinsics;
 
 #[cfg(any(target_arch = "x86_64", target_arch = "x86"))]
 use super::clmul as intrinsics;

polyval/src/backend/common.rs polyval/src/field_element/common.rspolyval/src/backend/common.rs renamed to polyval/src/field_element/common.rs

@@ -10,7 +10,7 @@ use core::arch::x86::*;
 use core::arch::x86_64::*;
 
 use super::FieldElement;
-use crate::{Block, Key, Tag, backend::common};
+use crate::{Block, Key, Tag, field_element::common};
 use core::{ops::Mul, ptr};
 use universal_hash::{
     KeyInit, ParBlocks, Reset, UhfBackend,

polyval/src/backend/soft.rs polyval/src/field_element/soft.rspolyval/src/backend/soft.rs renamed to polyval/src/field_element/soft.rs

@@ -6,10 +6,10 @@
     html_favicon_url = "https://raw.githubusercontent.com/RustCrypto/media/8f1a9894/logo.svg"
 )]
 
-mod backend;
+mod field_element;
 mod mulx;
 
-pub use crate::{backend::PolyvalGeneric, mulx::mulx};
+pub use crate::{field_element::PolyvalGeneric, mulx::mulx};
 pub use universal_hash;
 
 impl<const N: usize> core::fmt::Debug for PolyvalGeneric<N> {