clippy suggestion, loop iter enumerate

src/des.rs

@@ -132,12 +132,11 @@ fn key_schedule(key: u64) -> [u64; 16] {
 fn f(r: u32, subkey: u64) -> u32 {
     let expanded = permute(r as u64, &E, 32) ^ subkey;
     let mut s_out = 0u32;
-    // S-boxes
-    for i in 0..8 {
+    for (i, sbox) in SBOX.iter().enumerate() {
         let block = ((expanded >> (42 - 6 * i)) & 0x3F) as u8;
         let row = ((block & 0x20) >> 4) | (block & 1);
         let col = (block & 0x1E) >> 1;
-        let val = SBOX[i][row as usize][col as usize] as u32;
+        let val = sbox[row as usize][col as usize] as u32;
         s_out |= val << (28 - 4 * i);
     }
     permute(s_out as u64, &P, 32) as u32