chacha20: minor improvements

- lint `cfg`s
- add assertions
- avoid needless conversions

Author: dhardy

chacha20/Cargo.toml

@@ -47,3 +47,14 @@ xchacha = ["cipher"]
 [package.metadata.docs.rs]
 all-features = true
 rustdoc-args = ["--cfg", "docsrs"]
+
+[lints.rust.unexpected_cfgs]
+level = "warn"
+check-cfg = [
+  'cfg(chacha20_force_soft)',
+  'cfg(chacha20_force_sse2)',
+  'cfg(chacha20_force_avx2)',
+]
+
+[lints.clippy]
+needless_range_loop = "allow"

chacha20/src/backends/sse2.rs

@@ -116,7 +116,8 @@ where
 #[cfg(feature = "rng")]
 impl<R: Rounds> Backend<R> {
     #[inline(always)]
-    fn gen_ks_blocks(&mut self, block: &mut [u32]) {
+    fn gen_ks_blocks(&mut self, block: &mut [u32; 64]) {
+        const _: () = assert!(4 * PAR_BLOCKS * size_of::<__m128i>() == size_of::<[u32; 64]>());
         unsafe {
             let res = rounds::<R>(&self.v);
             self.v[3] = _mm_add_epi32(self.v[3], _mm_set_epi32(0, 0, 0, PAR_BLOCKS as i32));

chacha20/src/lib.rs

@@ -105,8 +105,6 @@
     html_logo_url = "https://raw.githubusercontent.com/RustCrypto/media/8f1a9894/logo.svg",
     html_favicon_url = "https://raw.githubusercontent.com/RustCrypto/media/8f1a9894/logo.svg"
 )]
-#![allow(clippy::needless_range_loop)]
-#![allow(unexpected_cfgs)]
 #![warn(missing_docs, rust_2018_idioms, trivial_casts, unused_qualifications)]
 
 #[cfg(feature = "cipher")]
@@ -228,10 +226,13 @@ impl<R: Rounds, V: Variant> ChaChaCore<R, V> {
     fn new(key: &[u8; 32], iv: &[u8]) -> Self {
         let mut state = [0u32; STATE_WORDS];
         state[0..4].copy_from_slice(&CONSTANTS);
+
         let key_chunks = key.chunks_exact(4);
         for (val, chunk) in state[4..12].iter_mut().zip(key_chunks) {
             *val = u32::from_le_bytes(chunk.try_into().unwrap());
         }
+
+        assert_eq!(iv.len(), 4 * (16 - V::NONCE_INDEX));
         let iv_chunks = iv.as_ref().chunks_exact(4);
         for (val, chunk) in state[V::NONCE_INDEX..16].iter_mut().zip(iv_chunks) {
             *val = u32::from_le_bytes(chunk.try_into().unwrap());

chacha20/src/rng.rs

@@ -214,7 +214,6 @@ const BUF_BLOCKS: u8 = BUFFER_SIZE as u8 >> 4;
 impl<R: Rounds, V: Variant> ChaChaCore<R, V> {
     /// Generates 4 blocks in parallel with avx2 & neon, but merely fills
     /// 4 blocks with sse2 & soft
-    #[cfg(feature = "rand_core")]
     fn generate(&mut self, buffer: &mut [u32; 64]) {
         cfg_if! {
             if #[cfg(chacha20_force_soft)] {
@@ -363,10 +362,6 @@ macro_rules! impl_chacha_rng {
             #[inline]
             fn generate(&mut self, r: &mut Self::Results) {
                 self.0.generate(&mut r.0);
-                #[cfg(target_endian = "big")]
-                for word in r.0.iter_mut() {
-                    *word = word.to_le();
-                }
             }
         }
 
@@ -744,6 +739,8 @@ pub(crate) mod tests {
         let mut rng1 = ChaChaRng::from_seed(seed);
         assert_eq!(rng1.next_u32(), 137206642);
 
+        assert_eq!(rng1.get_seed(), seed);
+
         let mut rng2 = ChaChaRng::from_rng(&mut rng1);
         assert_eq!(rng2.next_u32(), 1325750369);
     }