Hash collision security issue

Objects/unicodeobject.c

 /*
 
 Unicode implementation based on original code by Fredrik Lundh,
 modified by Marc-Andre Lemburg <mal@lemburg.com>.
 
 Major speed upgrades to the method implementations at the Reykjavik
 NeedForSpeed sprint, by Fredrik Lundh and Andrew Dalke.
 
 Copyright (c) Corporation for National Research Initiatives.
 
@@ skipping 11223 matching lines @@
     }
     }
     x ^= (Py_uhash_t)PyUnicode_GET_LENGTH(self);
 
     if (x == -1)
         x = -2;
     _PyUnicode_HASH(self) = x;
     return x;
 }
 #undef HASH
+
+Py_hash_t
+_PyUnicode_RandomizedHash(PyObject *self)
+{
+    Py_ssize_t len;
+    Py_uhash_t x;
+
+    if (PyUnicode_READY(self) == -1)
+        return -1;
+    len = PyUnicode_GET_LENGTH(self);
+    if (len == 0) {
+        _PyUnicode_HASH(self) = 0;
+        return 0;
+    }
+
+    /* Alternate definition of the hash function as a macro to above */
+#define HASH(P) \
+    x = _Py_HashSecret.prefix ^ (Py_uhash_t)*P << 7; \
+    while (--len >= 0) \
+        x = (_PyHASH_MULTIPLIER*x) ^ (Py_uhash_t)*P++;
+
+    switch (PyUnicode_KIND(self)) {
+    case PyUnicode_1BYTE_KIND: {
+        const unsigned char *c = PyUnicode_1BYTE_DATA(self);
+        HASH(c);
+        break;
+    }
+    case PyUnicode_2BYTE_KIND: {
+        const Py_UCS2 *s = PyUnicode_2BYTE_DATA(self);
+        HASH(s);
+        break;
+    }
+    default: {
+        Py_UCS4 *l;
+        assert(PyUnicode_KIND(self) == PyUnicode_4BYTE_KIND &&
+               "Impossible switch case in unicode_hash");
+        l = PyUnicode_4BYTE_DATA(self);
+        HASH(l);
+        break;
+    }
+    }
+    x ^= (Py_uhash_t)PyUnicode_GET_LENGTH(self);
+    x ^= _Py_HashSecret.suffix;
+
+    if (x == -1)
+        x = -2;
+    /* we do *not* update _PyUnicode_HASH(self) here */
+    return x;
+}
+#undef HASH
+
 
 PyDoc_STRVAR(index__doc__,
              "S.index(sub[, start[, end]]) -> int\n\
 \n\
 Like S.find() but raise ValueError when the substring is not found.");
 
 static PyObject *
 unicode_index(PyObject *self, PyObject *args)
 {
     Py_ssize_t result;
@@ skipping 3202 matching lines @@
 PyMODINIT_FUNC
 PyInit__string(void)
 {
     return PyModule_Create(&_string_module);
 }
 
 
 #ifdef __cplusplus
 }
 #endif