changeset 1172:38e4007378df

Added signed and unsigned methods to field elements.
author Janus Dam Nielsen <janus.nielsen@alexandra.dk>
date Wed, 29 Apr 2009 09:39:21 +0200
parents 0e3d8a3d3b15
children e86a007bddbd
files viff/field.py viff/test/test_signed_field.py
diffstat 2 files changed, 106 insertions(+), 1 deletions(-) [+]
line wrap: on
line diff
--- a/viff/field.py	Thu Apr 23 11:21:37 2009 +0200
+++ b/viff/field.py	Wed Apr 29 09:39:21 2009 +0200
@@ -505,6 +505,20 @@
             """Extract a bit (index is counted from zero)."""
             return (self.value >> index) & 1
 
+        def signed(self):
+            """Return a signed integer representation of the value.
+
+            If x > floor(p/2) then subtract p to obtain negative integer.
+            """
+            if self.value > ((self.modulus-1)/2):
+                return self.value - self.modulus
+            else:
+                return self.value
+
+        def unsigned(self):
+            """Return a unsigned representation of the value"""
+            return self.value
+
         def __repr__(self):
             return "{%d}" % self.value
             #return "GFElement(%d)" % self.value
@@ -514,7 +528,7 @@
 
             This is simply the value enclosed in curly braces.
             """
-            return "{%d}" % self.value
+            return "{%d}" % self.unsigned()
 
         def __eq__(self, other):
             """Equality test."""
@@ -626,3 +640,4 @@
 if __name__ == "__main__":
     import doctest    #pragma NO COVER
     doctest.testmod() #pragma NO COVER
+
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/viff/test/test_signed_field.py	Wed Apr 29 09:39:21 2009 +0200
@@ -0,0 +1,90 @@
+# Copyright 2009 VIFF Development Team.
+#
+# This file is part of VIFF, the Virtual Ideal Functionality Framework.
+#
+# VIFF is free software: you can redistribute it and/or modify it
+# under the terms of the GNU Lesser General Public License (LGPL) as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# VIFF is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+# or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General
+# Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with VIFF. If not, see <http://www.gnu.org/licenses/>.
+
+# Import system packages.
+import sys
+
+from twisted.trial.unittest import TestCase
+
+# Import VIFF packages.
+from viff.field import GF
+
+p = 30916444023318367583
+Zp = GF(p)
+
+class SignedVsUnsignedTest(TestCase):
+
+    def test_zero_minus_one_signed(self):
+        x = Zp(0)
+        y = Zp(1)
+        z = x - y
+        self.assertEquals(z.signed(), -1)       
+
+    def test_zero_minus_one_unsigned(self):
+        x = Zp(0)
+        y = Zp(1)
+        z = x - y
+        self.assertEquals(z.unsigned(), p-1)       
+
+    def test_maxint_plus_42_signed(self):
+        x = Zp(p)
+        y = Zp(42)
+        z = x + y
+        self.assertEquals(z.signed(), 42)
+
+    def test_little_subtracted_big_signed(self):
+        x = Zp(14)
+        y = Zp(42)
+        z = x - y
+        self.assertEquals(z.signed(), -28)       
+
+    def test_little_subtracted_big_unsigned(self):
+        x = Zp(14)
+        y = Zp(42)
+        z = x - y
+        self.assertEquals(z.unsigned(), p-28)       
+
+    def test_big_subtracted_little_signed(self):
+        x = Zp(42)
+        y = Zp(14)
+        z = x - y
+        self.assertEquals(z.signed(), 28)       
+
+    def test_big_subtracted_little_unsigned(self):
+        x = Zp(42)
+        y = Zp(14)
+        z = x - y
+        self.assertEquals(z.unsigned(), 28)       
+
+    def test_little_add_big_signed(self):
+        x = Zp(1)
+        y = Zp(p)
+        z = x + y
+        self.assertEquals(z.signed(), 1)
+
+    def test_little_add_big_unsigned(self):
+        x = Zp(1)
+        y = Zp(p)
+        z = x + y
+        self.assertEquals(z.unsigned(), 1)
+
+    def test_maxint_signed(self):
+        phalf = (p-1)/2
+        x = Zp(phalf)
+        y = Zp(1)
+        z = x + y 
+        self.assertEquals(z.signed(), -phalf)