--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -11,6 +11,76 @@ from i18n import gettext as _
 demandload(globals(), 'mdiff util')
 demandload(globals(), 'os sys')
 
+revrangesep = ':'
+
+def revfix(repo, val, defval):
+    '''turn user-level id of changeset into rev number.
+    user-level id can be tag, changeset, rev number, or negative rev
+    number relative to number of revs (-1 is tip, etc).'''
+    if not val:
+        return defval
+    try:
+        num = int(val)
+        if str(num) != val:
+            raise ValueError
+        if num < 0:
+            num += repo.changelog.count()
+        if num < 0:
+            num = 0
+        elif num >= repo.changelog.count():
+            raise ValueError
+    except ValueError:
+        try:
+            num = repo.changelog.rev(repo.lookup(val))
+        except KeyError:
+            raise util.Abort(_('invalid revision identifier %s') % val)
+    return num
+
+def revpair(ui, repo, revs):
+    '''return pair of nodes, given list of revisions. second item can
+    be None, meaning use working dir.'''
+    if not revs:
+        return repo.dirstate.parents()[0], None
+    end = None
+    if len(revs) == 1:
+        start = revs[0]
+        if revrangesep in start:
+            start, end = start.split(revrangesep, 1)
+            start = revfix(repo, start, 0)
+            end = revfix(repo, end, repo.changelog.count() - 1)
+        else:
+            start = revfix(repo, start, None)
+    elif len(revs) == 2:
+        if revrangesep in revs[0] or revrangesep in revs[1]:
+            raise util.Abort(_('too many revisions specified'))
+        start = revfix(repo, revs[0], None)
+        end = revfix(repo, revs[1], None)
+    else:
+        raise util.Abort(_('too many revisions specified'))
+    if end is not None: end = repo.lookup(str(end))
+    return repo.lookup(str(start)), end
+
+def revrange(ui, repo, revs):
+    """Yield revision as strings from a list of revision specifications."""
+    seen = {}
+    for spec in revs:
+        if revrangesep in spec:
+            start, end = spec.split(revrangesep, 1)
+            start = revfix(repo, start, 0)
+            end = revfix(repo, end, repo.changelog.count() - 1)
+            step = start > end and -1 or 1
+            for rev in xrange(start, end+step, step):
+                if rev in seen:
+                    continue
+                seen[rev] = 1
+                yield str(rev)
+        else:
+            rev = revfix(repo, spec, None)
+            if rev in seen:
+                continue
+            seen[rev] = 1
+            yield str(rev)
+
 def make_filename(repo, pat, node,
                   total=None, seqno=None, revwidth=None, pathname=None):
     node_expander = {