safety considerations

src/main.rs

@@ -204,7 +204,7 @@ impl SField {
 
     #[inline(always)]
     fn print(&self) {
-        for i in 0..self.size * self.size {
+        for i in 0..self.num_fields {
             if i != 0 && i % self.size == 0 {
                 println!();
             }
@@ -273,10 +273,12 @@ impl SField {
     fn put_valid_nr(&mut self) -> bool {
         let current_nr = self.get_field_at_pos(self.pos);
 
+        // safety:
+        //     self.possible_vals is initialized with self.size * self.size
+        //     so self.pos can safely be used to index here
         let possible_vals = unsafe { self.possible_values.get_unchecked(self.pos) };
 
-        for idx in 0..possible_vals.len() {
-            let nr = unsafe { possible_vals.get_unchecked(idx) };
+        for nr in possible_vals.iter() {
             if *nr <= current_nr {
                 continue;
             }
@@ -308,11 +310,18 @@ impl SField {
 
     #[inline(always)]
     fn is_fixed(&self) -> bool {
+        // safety: self.pos can be used to index the field unchecked
+        //         since the only methods modifying self.pos are
+        //         `next()` and `prev()` and they do bounds checking
         unsafe { *self.fixed.get_unchecked(self.pos) == 1 }
     }
 
     #[inline(always)]
     fn get_field_at_pos(&self, pos: usize) -> usize {
+        // safety:
+        //     TODO
+        //     would need to mathematically explain that the calculations in
+        //     get_row(), get_col() and get_block() can never exceed 0..self.num_fields
         unsafe { *self.field.get_unchecked(pos) }
     }