fix typos in backtrack.rs

Author: seeekr

src/backtrack.rs

@@ -13,7 +13,7 @@
 // regexes on small inputs because of its memory requirements.
 //
 // In particular, this is a *bounded* backtracking engine. It retains worst
-// case linear time by keeping track of the states that is has visited (using a
+// case linear time by keeping track of the states that it has visited (using a
 // bitmap). Namely, once a state is visited, it is never visited again. Since a
 // state is keyed by `(instruction index, input index)`, we have that its time
 // complexity is `O(mn)` (i.e., linear in the size of the search text).
@@ -36,7 +36,7 @@ type Bits = u32;
 const BIT_SIZE: usize = 32;
 const MAX_SIZE_BYTES: usize = 256 * (1 << 10); // 256 KB
 
-/// Returns true iff the given regex and input should be executed by this
+/// Returns true if the given regex and input should be executed by this
 /// engine with reasonable memory usage.
 pub fn should_exec(num_insts: usize, text_len: usize) -> bool {
     // Total memory usage in bytes is determined by: