Internals: Polyfill array_map.

Cargo.toml

@@ -212,6 +212,7 @@ include = [
     "src/pbkdf2.rs",
     "src/pkcs8.rs",
     "src/polyfill.rs",
+    "src/polyfill/array_map.rs",
     "src/polyfill/chunks_fixed.rs",
     "src/rand.rs",
     "src/rsa/convert_nist_rsa_test_vectors.py",

src/aead/chacha.rs

@@ -14,7 +14,7 @@
 // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 
 use super::{quic::Sample, Nonce};
-use crate::polyfill::ChunksFixed;
+use crate::polyfill::{array_map::Map, ChunksFixed};
 
 #[cfg(any(
     test,
@@ -35,17 +35,8 @@ pub struct Key([u32; KEY_LEN / 4]);
 impl From<[u8; KEY_LEN]> for Key {
     #[inline]
     fn from(value: [u8; KEY_LEN]) -> Self {
-        let value = value.chunks_fixed();
-        Self([
-            u32::from_le_bytes(value[0]),
-            u32::from_le_bytes(value[1]),
-            u32::from_le_bytes(value[2]),
-            u32::from_le_bytes(value[3]),
-            u32::from_le_bytes(value[4]),
-            u32::from_le_bytes(value[5]),
-            u32::from_le_bytes(value[6]),
-            u32::from_le_bytes(value[7]),
-        ])
+        let value: &[[u8; 4]; KEY_LEN / 4] = value.chunks_fixed();
+        Self(value.array_map(u32::from_le_bytes))
     }
 }
 
@@ -202,12 +193,7 @@ pub struct Iv([u32; 4]);
 impl Iv {
     fn assume_unique_for_key(value: [u8; 16]) -> Self {
         let value: &[[u8; 4]; 4] = value.chunks_fixed();
-        Self([
-            u32::from_le_bytes(value[0]),
-            u32::from_le_bytes(value[1]),
-            u32::from_le_bytes(value[2]),
-            u32::from_le_bytes(value[3]),
-        ])
+        Self(value.array_map(u32::from_le_bytes))
     }
 
     fn into_counter_for_single_block_less_safe(self) -> Counter {

src/digest.rs

@@ -24,6 +24,7 @@
 // The goal for this implementation is to drive the overhead as close to zero
 // as possible.
 
+use crate::polyfill::array_map::Map;
 use crate::{
     c, cpu, debug,
     endian::{ArrayEncoding, BigEndian},
@@ -463,32 +464,14 @@ pub const MAX_CHAINING_LEN: usize = MAX_OUTPUT_LEN;
 fn sha256_format_output(input: State) -> Output {
     let input = unsafe { &input.as32 };
     Output {
-        as32: [
-            BigEndian::from(input[0]),
-            BigEndian::from(input[1]),
-            BigEndian::from(input[2]),
-            BigEndian::from(input[3]),
-            BigEndian::from(input[4]),
-            BigEndian::from(input[5]),
-            BigEndian::from(input[6]),
-            BigEndian::from(input[7]),
-        ],
+        as32: input.array_map(BigEndian::from),
     }
 }
 
 fn sha512_format_output(input: State) -> Output {
     let input = unsafe { &input.as64 };
     Output {
-        as64: [
-            BigEndian::from(input[0]),
-            BigEndian::from(input[1]),
-            BigEndian::from(input[2]),
-            BigEndian::from(input[3]),
-            BigEndian::from(input[4]),
-            BigEndian::from(input[5]),
-            BigEndian::from(input[6]),
-            BigEndian::from(input[7]),
-        ],
+        as64: input.array_map(BigEndian::from),
     }
 }
 

src/polyfill.rs

@@ -41,4 +41,6 @@ pub mod slice {
 #[macro_use]
 mod chunks_fixed;
 
+pub(crate) mod array_map;
+
 pub use chunks_fixed::*;

src/polyfill/array_map.rs

@@ -0,0 +1,36 @@
+// Copyright 2015-2016 Brian Smith.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
+// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+// TODO: Replace this with use of the array_map feature
+// (https://github.com/rust-lang/rust/issues/75243) when it becomes stable.
+
+pub(crate) trait Map<A, B, BArray> {
+    fn array_map(self, f: impl Fn(A) -> B) -> BArray;
+}
+
+impl<A, B> Map<A, B, [B; 4]> for [A; 4] {
+    #[inline]
+    fn array_map(self, f: impl Fn(A) -> B) -> [B; 4] {
+        let [a0, a1, a2, a3] = self;
+        [f(a0), f(a1), f(a2), f(a3)]
+    }
+}
+
+impl<A, B> Map<A, B, [B; 8]> for [A; 8] {
+    #[inline]
+    fn array_map(self, f: impl Fn(A) -> B) -> [B; 8] {
+        let [a0, a1, a2, a3, a4, a5, a6, a7] = self;
+        [f(a0), f(a1), f(a2), f(a3), f(a4), f(a5), f(a6), f(a7)]
+    }
+}