From d50fca63d26e92b39213b0bd3791dba5c03b951b Mon Sep 17 00:00:00 2001
From: Tony Arcieri <bascule@gmail.com>
Date: Sat, 25 Feb 2023 16:36:54 -0700
Subject: [PATCH] ascon: eliminate `util` module (#38)

Factors the `u8` <-> `u64` conversions to be inline
---
 ascon/src/lib.rs  | 14 +++++++++-----
 ascon/src/util.rs | 16 ----------------
 2 files changed, 9 insertions(+), 21 deletions(-)
 delete mode 100644 ascon/src/util.rs

diff --git a/ascon/src/lib.rs b/ascon/src/lib.rs
index 3d59bec..4833db7 100644
--- a/ascon/src/lib.rs
+++ b/ascon/src/lib.rs
@@ -41,9 +41,7 @@ extern crate alloc;
 #[cfg(feature = "alloc")]
 pub mod aead;
 
-mod util;
-
-use crate::util::{u64_to_u8, u8_to_u64};
+use core::convert::TryInto;
 
 /// Key length.
 const KEY_LEN: usize = 16;
@@ -64,7 +62,11 @@ const B: usize = 8;
 pub fn permutation(s: &mut [u8], start: usize, rounds: usize) {
     let mut x = [0; 5];
     let mut t = [0; 5];
-    u8_to_u64(s, &mut x);
+
+    #[allow(clippy::unwrap_used)]
+    for (i, b) in x.iter_mut().enumerate() {
+        *b = u64::from_be_bytes(s[(i * 8)..((i + 1) * 8)].try_into().unwrap());
+    }
 
     for i in start as u64..(start + rounds) as u64 {
         x[2] ^= ((0xfu64 - i) << 4) | i;
@@ -104,7 +106,9 @@ pub fn permutation(s: &mut [u8], start: usize, rounds: usize) {
         x[4] ^= x[4].rotate_right(7) ^ x[4].rotate_right(41);
     }
 
-    u64_to_u8(&x, s);
+    for (i, &b) in x.iter().enumerate() {
+        s[(i * 8)..((i + 1) * 8)].copy_from_slice(&b.to_be_bytes())
+    }
 }
 
 /// Initialize Ascon permutation.
diff --git a/ascon/src/util.rs b/ascon/src/util.rs
deleted file mode 100644
index d400a61..0000000
--- a/ascon/src/util.rs
+++ /dev/null
@@ -1,16 +0,0 @@
-use core::convert::TryInto;
-
-#[inline]
-#[allow(clippy::unwrap_used)]
-pub fn u8_to_u64(input: &[u8], output: &mut [u64]) {
-    for (i, b) in output.iter_mut().enumerate() {
-        *b = u64::from_be_bytes(input[(i * 8)..((i + 1) * 8)].try_into().unwrap());
-    }
-}
-
-#[inline]
-pub fn u64_to_u8(input: &[u64], output: &mut [u8]) {
-    for (i, &b) in input.iter().enumerate() {
-        output[(i * 8)..((i + 1) * 8)].copy_from_slice(&b.to_be_bytes())
-    }
-}