diff --git a/mercurial/pure/bdiff.py b/mercurial/pure/bdiff.py
--- a/mercurial/pure/bdiff.py
+++ b/mercurial/pure/bdiff.py
@@ -12,6 +12,10 @@ import difflib
 import re
 import struct
 
+from . import policy
+policynocffi = policy.policynocffi
+modulepolicy = policy.policy
+
 def splitnewlines(text):
     '''like str.splitlines, but only split on newlines.'''
     lines = [l + '\n' for l in text.split('\n')]
@@ -96,3 +100,37 @@ def fixws(text, allws):
         text = re.sub('[ \t\r]+', ' ', text)
         text = text.replace(' \n', '\n')
     return text
+
+if modulepolicy not in policynocffi:
+    try:
+        from _bdiff_cffi import ffi, lib
+    except ImportError:
+        if modulepolicy == 'cffi': # strict cffi import
+            raise
+    else:
+        def blocks(sa, sb):
+            a = ffi.new("struct bdiff_line**")
+            b = ffi.new("struct bdiff_line**")
+            ac = ffi.new("char[]", sa)
+            bc = ffi.new("char[]", sb)
+            try:
+                an = lib.bdiff_splitlines(ac, len(sa), a)
+                bn = lib.bdiff_splitlines(bc, len(sb), b)
+                if not a[0] or not b[0]:
+                    raise MemoryError
+                l = ffi.new("struct bdiff_hunk*")
+                count = lib.bdiff_diff(a[0], an, b[0], bn, l)
+                if count < 0:
+                    raise MemoryError
+                rl = [None] * count
+                h = l.next
+                i = 0
+                while h:
+                    rl[i] = (h.a1, h.a2, h.b1, h.b2)
+                    h = h.next
+                    i += 1
+            finally:
+                lib.free(a[0])
+                lib.free(b[0])
+                lib.bdiff_freehunks(l.next)
+            return rl
diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -319,7 +319,9 @@ class hgbuildpy(build_py):
             self.distribution.ext_modules = []
         elif self.distribution.cffi:
             import setup_mpatch_cffi
-            exts = [setup_mpatch_cffi.ffi.distutils_extension()]
+            import setup_bdiff_cffi
+            exts = [setup_mpatch_cffi.ffi.distutils_extension(),
+                    setup_bdiff_cffi.ffi.distutils_extension()]
             # cffi modules go here
             if sys.platform == 'darwin':
                 import setup_osutil_cffi
diff --git a/setup_bdiff_cffi.py b/setup_bdiff_cffi.py
new file mode 100644
--- /dev/null
+++ b/setup_bdiff_cffi.py
@@ -0,0 +1,31 @@
+from __future__ import absolute_import
+
+import cffi
+import os
+
+ffi = cffi.FFI()
+ffi.set_source("_bdiff_cffi",
+    open(os.path.join(os.path.join(os.path.dirname(__file__), 'mercurial'),
+        'bdiff.c')).read(), include_dirs=['mercurial'])
+ffi.cdef("""
+struct bdiff_line {
+    int hash, n, e;
+    ssize_t len;
+    const char *l;
+};
+
+struct bdiff_hunk;
+struct bdiff_hunk {
+    int a1, a2, b1, b2;
+    struct bdiff_hunk *next;
+};
+
+int bdiff_splitlines(const char *a, ssize_t len, struct bdiff_line **lr);
+int bdiff_diff(struct bdiff_line *a, int an, struct bdiff_line *b, int bn,
+    struct bdiff_hunk *base);
+void bdiff_freehunks(struct bdiff_hunk *l);
+void free(void*);
+""")
+
+if __name__ == '__main__':
+    ffi.compile()