Merge pull request #6 from project-rig/fix-probability-scaling

Fix probability scaling
SpiNNakerManchester · Jun 21, 2016 · e8d964d · e8d964d
2 parents 11930e1 + 987afb0
commit e8d964d
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Showing 2 changed files with 8 additions and 6 deletions.
diff --git a/network_tester/commands.py b/network_tester/commands.py
@@ -316,10 +316,10 @@ def probability(self, source_num, probability):
         if self._probability[source_num] != probability:
             self._probability[source_num] = probability
             # Convert to value between 0 and 0xFFFFFFFF
-            if probability == 1.0:
+            if probability >= 1.0:
                 probability = 0xFFFFFFFF
             else:
-                probability = int(round(probability * (1 << 32)))
+                probability = int(round(probability * ((1 << 32) - 1)))
             self._commands.extend([NT_CMD.PROBABILITY | (source_num << 8),
                                    probability])
 

diff --git a/tests/test_commands.py b/tests/test_commands.py
@@ -252,18 +252,20 @@ def test_probability():
     a.probability(1, 0.0)
     assert len(a._commands) == 2
 
-    # If should produce command on change
-    a.probability(0, 0.5)
+    # If changed should produce command on change. Note that in this test we
+    # check that very-nearly-one values get rounded up to one. Previously an
+    # off-by-one bug rounded up *past* one.
+    a.probability(0, 0.9999999999999999)
     assert len(a._commands) == 4
     assert a._commands[-2:] == [NT_CMD.PROBABILITY | (0 << 8),
-                                1 << 31]
+                                (1 << 32) - 1]
     a.probability(1, 0.25)
     assert len(a._commands) == 6
     assert a._commands[-2:] == [NT_CMD.PROBABILITY | (1 << 8),
                                 1 << 30]
 
     # No command should be produced on non-change again
-    a.probability(0, 0.5)
+    a.probability(0, 0.9999999999999999)
     a.probability(1, 0.25)
     assert len(a._commands) == 6