diff --git a/src/libregex/re.rs b/src/libregex/re.rs
index 6569f047abae..b40968283bd5 100644
--- a/src/libregex/re.rs
+++ b/src/libregex/re.rs
@@ -477,14 +477,13 @@ impl Regex {
                    (&self, text: &str, limit: uint, mut rep: R) -> StrBuf {
         let mut new = StrBuf::with_capacity(text.len());
         let mut last_match = 0u;
-        let mut i = 0;
-        for cap in self.captures_iter(text) {
+
+        for (i, cap) in self.captures_iter(text).enumerate() {
             // It'd be nicer to use the 'take' iterator instead, but it seemed
             // awkward given that '0' => no limit.
             if limit > 0 && i >= limit {
                 break
             }
-            i += 1;
 
             let (s, e) = cap.pos(0).unwrap(); // captures only reports matches
             new.push_str(text.slice(last_match, s));
@@ -800,7 +799,7 @@ impl<'r, 't> Iterator<Captures<'t>> for FindCaptures<'r, 't> {
 
         // Don't accept empty matches immediately following a match.
         // i.e., no infinite loops please.
-        if e - s == 0 && Some(self.last_end) == self.last_match {
+        if e == s && Some(self.last_end) == self.last_match {
             self.last_end += 1;
             return self.next()
         }
@@ -842,7 +841,7 @@ impl<'r, 't> Iterator<(uint, uint)> for FindMatches<'r, 't> {
 
         // Don't accept empty matches immediately following a match.
         // i.e., no infinite loops please.
-        if e - s == 0 && Some(self.last_end) == self.last_match {
+        if e == s && Some(self.last_end) == self.last_match {
             self.last_end += 1;
             return self.next()
         }
diff --git a/src/libregex/vm.rs b/src/libregex/vm.rs
index 6058ba6bf921..ea89c8986930 100644
--- a/src/libregex/vm.rs
+++ b/src/libregex/vm.rs
@@ -169,17 +169,15 @@ impl<'r, 't> Nfa<'r, 't> {
             self.ic = next_ic;
             next_ic = self.chars.advance();
 
-            let mut i = 0;
-            while i < clist.size {
+            for i in range(0, clist.size) {
                 let pc = clist.pc(i);
                 let step_state = self.step(groups.as_mut_slice(), nlist,
                                            clist.groups(i), pc);
                 match step_state {
                     StepMatchEarlyReturn => return vec![Some(0), Some(0)],
-                    StepMatch => { matched = true; clist.empty() },
+                    StepMatch => { matched = true; break },
                     StepContinue => {},
                 }
-                i += 1;
             }
             mem::swap(&mut clist, &mut nlist);
             nlist.empty();
@@ -226,7 +224,7 @@ impl<'r, 't> Nfa<'r, 't> {
                     let found = ranges.as_slice();
                     let found = found.bsearch(|&rc| class_cmp(casei, c, rc));
                     let found = found.is_some();
-                    if (found && !negate) || (!found && negate) {
+                    if found ^ negate {
                         self.add(nlist, pc+1, caps);
                     }
                 }
@@ -568,20 +566,10 @@ pub fn find_prefix(needle: &[u8], haystack: &[u8]) -> Option<uint> {
     if nlen > hlen || nlen == 0 {
         return None
     }
-    let mut hayi = 0u;
-    'HAYSTACK: loop {
-        if hayi > hlen - nlen {
-            break
+    for (offset, window) in haystack.windows(nlen).enumerate() {
+        if window == needle {
+            return Some(offset)
         }
-        let mut nedi = 0;
-        while nedi < nlen {
-            if haystack[hayi+nedi] != needle[nedi] {
-                hayi += 1;
-                continue 'HAYSTACK
-            }
-            nedi += 1;
-        }
-        return Some(hayi)
     }
     None
 }
diff --git a/src/libregex_macros/lib.rs b/src/libregex_macros/lib.rs
index 5445c5f67617..8b134d5af8bb 100644
--- a/src/libregex_macros/lib.rs
+++ b/src/libregex_macros/lib.rs
@@ -187,18 +187,16 @@ fn exec<'t>(which: ::regex::native::MatchKind, input: &'t str,
                 self.ic = next_ic;
                 next_ic = self.chars.advance();
 
-                let mut i = 0;
-                while i < clist.size {
+                for i in range(0, clist.size) {
                     let pc = clist.pc(i);
                     let step_state = self.step(&mut groups, nlist,
                                                clist.groups(i), pc);
                     match step_state {
                         StepMatchEarlyReturn =>
                             return vec![Some(0u), Some(0u)],
-                        StepMatch => { matched = true; clist.empty() },
+                        StepMatch => { matched = true; break },
                         StepContinue => {},
                     }
-                    i += 1;
                 }
                 ::std::mem::swap(&mut clist, &mut nlist);
                 nlist.empty();