feat: simplify hash(&[u8])

src/hash/rescue/rpo/mod.rs

@@ -84,18 +84,11 @@ impl Hasher for Rpo256 {
         // into the state.
         //
         // every time the rate range is filled, a permutation is performed. if the final value of
-        // `i` is not zero, then the chunks count wasn't enough to fill the state range, and an
-        // additional permutation must be performed.
-        let mut current_element = 0_usize;
-        // handle the case of an empty `bytes`
-        let last_element = if num_field_elem == 0 {
-            current_element
-        } else {
-            num_field_elem - 1
-        };
-        let i = bytes.chunks(BINARY_CHUNK_SIZE).fold(0, |i, chunk| {
+        // `rate_pos` is not zero, then the chunks count wasn't enough to fill the state range,
+        // and an additional permutation must be performed.
+        let rate_pos = bytes.chunks(BINARY_CHUNK_SIZE).fold(0, |rate_pos, chunk| {
             // copy the chunk into the buffer
-            if current_element != last_element {
+            if chunk.len() == BINARY_CHUNK_SIZE {
                 buf[..BINARY_CHUNK_SIZE].copy_from_slice(chunk);
             } else {
                 // on the last iteration, we pad `buf` with a 1 followed by as many 0's as are
@@ -104,19 +97,18 @@ impl Hasher for Rpo256 {
                 buf[..chunk.len()].copy_from_slice(chunk);
                 buf[chunk.len()] = 1;
             }
-            current_element += 1;
 
             // set the current rate element to the input. since we take at most 7 bytes, we are
             // guaranteed that the inputs data will fit into a single field element.
-            state[RATE_RANGE.start + i] = Felt::new(u64::from_le_bytes(buf));
+            state[RATE_RANGE.start + rate_pos] = Felt::new(u64::from_le_bytes(buf));
 
             // proceed filling the range. if it's full, then we apply a permutation and reset the
             // counter to the beginning of the range.
-            if i == RATE_WIDTH - 1 {
+            if rate_pos == RATE_WIDTH - 1 {
                 Self::apply_permutation(&mut state);
                 0
             } else {
-                i + 1
+                rate_pos + 1
             }
         });
 
@@ -125,8 +117,8 @@ impl Hasher for Rpo256 {
         // don't need to apply any extra padding because the first capacity element contains a
         // flag indicating the number of field elements constituting the last block when the latter
         // is not divisible by `RATE_WIDTH`.
-        if i != 0 {
-            state[RATE_RANGE.start + i..RATE_RANGE.end].fill(ZERO);
+        if rate_pos != 0 {
+            state[RATE_RANGE.start + rate_pos..RATE_RANGE.end].fill(ZERO);
             Self::apply_permutation(&mut state);
         }
 

src/hash/rescue/rpx/mod.rs

@@ -89,18 +89,11 @@ impl Hasher for Rpx256 {
         // into the state.
         //
         // every time the rate range is filled, a permutation is performed. if the final value of
-        // `i` is not zero, then the chunks count wasn't enough to fill the state range, and an
-        // additional permutation must be performed.
-        let mut current_element = 0_usize;
-        // handle the case of an empty `bytes`
-        let last_element = if num_field_elem == 0 {
-            current_element
-        } else {
-            num_field_elem - 1
-        };
-        let i = bytes.chunks(BINARY_CHUNK_SIZE).fold(0, |i, chunk| {
+        // `rate_pos` is not zero, then the chunks count wasn't enough to fill the state range,
+        // and an additional permutation must be performed.
+        let rate_pos = bytes.chunks(BINARY_CHUNK_SIZE).fold(0, |rate_pos, chunk| {
             // copy the chunk into the buffer
-            if current_element != last_element {
+            if chunk.len() == BINARY_CHUNK_SIZE {
                 buf[..BINARY_CHUNK_SIZE].copy_from_slice(chunk);
             } else {
                 // on the last iteration, we pad `buf` with a 1 followed by as many 0's as are
@@ -109,19 +102,18 @@ impl Hasher for Rpx256 {
                 buf[..chunk.len()].copy_from_slice(chunk);
                 buf[chunk.len()] = 1;
             }
-            current_element += 1;
 
             // set the current rate element to the input. since we take at most 7 bytes, we are
             // guaranteed that the inputs data will fit into a single field element.
-            state[RATE_RANGE.start + i] = Felt::new(u64::from_le_bytes(buf));
+            state[RATE_RANGE.start + rate_pos] = Felt::new(u64::from_le_bytes(buf));
 
             // proceed filling the range. if it's full, then we apply a permutation and reset the
             // counter to the beginning of the range.
-            if i == RATE_WIDTH - 1 {
+            if rate_pos == RATE_WIDTH - 1 {
                 Self::apply_permutation(&mut state);
                 0
             } else {
-                i + 1
+                rate_pos + 1
             }
         });
 
@@ -130,8 +122,8 @@ impl Hasher for Rpx256 {
         // don't need to apply any extra padding because the first capacity element contains a
         // flag indicating the number of field elements constituting the last block when the latter
         // is not divisible by `RATE_WIDTH`.
-        if i != 0 {
-            state[RATE_RANGE.start + i..RATE_RANGE.end].fill(ZERO);
+        if rate_pos != 0 {
+            state[RATE_RANGE.start + rate_pos..RATE_RANGE.end].fill(ZERO);
             Self::apply_permutation(&mut state);
         }