* Fix short string optimization in strings.pyx. StringStore tests now all pass.

spacy/strings.pyx

@@ -18,45 +18,46 @@ cpdef hash_t hash_string(unicode string) except 0:
 
 
 cdef unicode _decode(const Utf8Str* string):
+    cdef int i, length
     if string.s[0] < sizeof(string.s) and string.s[0] != 0:
         return string.s[1:string.s[0]+1].decode('utf8')
-    elif string.p[0] < 256:
+    elif string.p[0] < 255:
         return string.p[1:string.p[0]+1].decode('utf8')
     else:
-        raise Exception(string.p[0])
-    cdef int i = 0
-    cdef int length = 0
+        i = 0
+        length = 0
         while string.p[i] == 255:
             i += 1
             length += 255
         length += string.p[i]
         i += 1
-    return string.p[i:length - i].decode('utf8')
+        return string.p[i:length + i].decode('utf8')
 
 
 cdef Utf8Str _allocate(Pool mem, const unsigned char* chars, int length) except *:
+    cdef int n_length_bytes
+    cdef int i
     cdef Utf8Str string
     assert length != 0
     if length < sizeof(string.s):
         string.s[0] = <unsigned char>length
         memcpy(&string.s[1], chars, length)
         return string
-    elif length < 256:
+    elif length < 255:
         string.p = <unsigned char*>mem.alloc(length + 1, sizeof(unsigned char))
         string.p[0] = length
         memcpy(&string.p[1], chars, length)
         assert string.s[0] >= sizeof(string.s) or string.s[0] == 0, string.s[0]
         return string
     else:
-        raise Exception(length)
-    cdef int n_length_bytes = (length // 256) + ((length % 256) != 0)
-    cdef int i = 0
-    while length >= 256:
+        i = 0
+        n_length_bytes = (length // 255) + 1
+        string.p = <unsigned char*>mem.alloc(length + n_length_bytes, sizeof(unsigned char))
+        for i in range(n_length_bytes-1):
             string.p[i] = 255
-        length -= 255
-        i += 1
-    string.p[i] = length
-    memcpy(&string.p[i+1], chars, length)
+        string.p[n_length_bytes-1] = length % 255
+        memcpy(&string.p[n_length_bytes], chars, length)
+        assert string.s[0] >= sizeof(string.s) or string.s[0] == 0, string.s[0]
         return string
 
 
@@ -87,9 +88,13 @@ cdef class StringStore:
             utf8str = &self.c[<int>string_or_id]
             return _decode(utf8str)
         elif isinstance(string_or_id, bytes):
+            if len(string_or_id) == 0:
+                return 0
             utf8str = self.intern(<unsigned char*>string_or_id, len(string_or_id))
             return utf8str - self.c
         elif isinstance(string_or_id, unicode):
+            if len(string_or_id) == 0:
+                return 0
             byte_string = string_or_id.encode('utf8')
             utf8str = self.intern(<unsigned char*>byte_string, len(byte_string))
             return utf8str - self.c