From 2c3a67b693da506ca4b523743969ee6757e98b22 Mon Sep 17 00:00:00 2001
From: Matthew Honnibal <honnibal+gh@gmail.com>
Date: Sun, 23 Oct 2016 14:49:31 +0200
Subject: [PATCH] Fix calculation of vector norm, re Issue #522. Need to
 consolidate the calculations into a helper function.

---
 spacy/tokens/doc.pyx  | 9 +++++----
 spacy/tokens/span.pyx | 9 +++++----
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/spacy/tokens/doc.pyx b/spacy/tokens/doc.pyx
index 0fe5dc4ff..4e292d623 100644
--- a/spacy/tokens/doc.pyx
+++ b/spacy/tokens/doc.pyx
@@ -1,12 +1,12 @@
 cimport cython
 from libc.string cimport memcpy, memset
 from libc.stdint cimport uint32_t
+from libc.math cimport sqrt
 
 import numpy
 import numpy.linalg
 import struct
 cimport numpy as np
-import math
 import six
 import warnings
 
@@ -251,11 +251,12 @@ cdef class Doc:
             if 'vector_norm' in self.user_hooks:
                 return self.user_hooks['vector_norm'](self)
             cdef float value
+            cdef double norm = 0
             if self._vector_norm is None:
-                self._vector_norm = 1e-20
+                norm = 0.0
                 for value in self.vector:
-                    self._vector_norm += value * value
-                self._vector_norm = math.sqrt(self._vector_norm)
+                    norm += value * value
+                self._vector_norm = sqrt(norm) if norm != 0 else 0
             return self._vector_norm
         
         def __set__(self, value):
diff --git a/spacy/tokens/span.pyx b/spacy/tokens/span.pyx
index 2cac2d947..033c74c56 100644
--- a/spacy/tokens/span.pyx
+++ b/spacy/tokens/span.pyx
@@ -3,7 +3,7 @@ from collections import defaultdict
 import numpy
 import numpy.linalg
 cimport numpy as np
-import math
+from libc.math cimport sqrt
 import six
 
 from ..structs cimport TokenC, LexemeC
@@ -136,11 +136,12 @@ cdef class Span:
             if 'vector_norm' in self.doc.user_span_hooks:
                 return self.doc.user_span_hooks['vector'](self)
             cdef float value
+            cdef double norm = 0
             if self._vector_norm is None:
-                self._vector_norm = 1e-20
+                norm = 0
                 for value in self.vector:
-                    self._vector_norm += value * value
-                self._vector_norm = math.sqrt(self._vector_norm)
+                    norm += value * value
+                self._vector_norm = sqrt(norm) if norm != 0 else 0
             return self._vector_norm
 
     property text: