add a comment explaining that hash_slice input data size must be a multiple of 8. Thanks @sanjay-sol for reporting this undocumented behaviour.

Author: TomWambsgans

crates/backend/symetric/src/sponge.rs

@@ -3,13 +3,15 @@
 use crate::Compression;
 
 // IV should have been added to data when necessary (typically: when the length of the data beeing hashed is not constant). Maybe we should re-add IV all the time for simplicity?
+// assumes data length is a multiple of RATE (= 8 in practice).
 pub fn hash_slice<T, Comp, const WIDTH: usize, const RATE: usize, const OUT: usize>(comp: &Comp, data: &[T]) -> [T; OUT]
 where
     T: Default + Copy,
     Comp: Compression<[T; WIDTH]>,
 {
     debug_assert!(RATE == OUT);
     debug_assert!(WIDTH == OUT + RATE);
+    debug_assert!(data.len().is_multiple_of(RATE));
     let n_chunks = data.len() / RATE;
     debug_assert!(n_chunks >= 2);
     let mut state: [T; WIDTH] = data[data.len() - WIDTH..].try_into().unwrap();