Address github comments

tools/profiling/microbenchmarks/bm_diff/bm_speedup.py

@@ -30,8 +30,7 @@
 from scipy import stats
 import math
 
-_THRESHOLD = 1e-10
-
+_DEFAULT_THRESHOLD = 1e-10
 
 def scale(a, mul):
   return [x * mul for x in a]
@@ -40,19 +39,18 @@ def scale(a, mul):
 def cmp(a, b):
   return stats.ttest_ind(a, b)
 
-
-def speedup(new, old):
+def speedup(new, old, threshold = _DEFAULT_THRESHOLD):
   if (len(set(new))) == 1 and new == old: return 0
   s0, p0 = cmp(new, old)
   if math.isnan(p0): return 0
   if s0 == 0: return 0
-  if p0 > _THRESHOLD: return 0
+  if p0 > _DEFAULT_THRESHOLD: return 0
   if s0 < 0:
     pct = 1
     while pct < 100:
       sp, pp = cmp(new, scale(old, 1 - pct / 100.0))
       if sp > 0: break
-      if pp > _THRESHOLD: break
+      if pp > _DEFAULT_THRESHOLD: break
       pct += 1
     return -(pct - 1)
   else:
@@ -60,13 +58,13 @@ def speedup(new, old):
     while pct < 10000:
       sp, pp = cmp(new, scale(old, 1 + pct / 100.0))
       if sp < 0: break
-      if pp > _THRESHOLD: break
+      if pp > _DEFAULT_THRESHOLD: break
       pct += 1
     return pct - 1
 
 
 if __name__ == "__main__":
   new = [0.0, 0.0, 0.0, 0.0] 
-  old=[2.96608e-06, 3.35076e-06, 3.45384e-06, 3.34407e-06]
+  old = [2.96608e-06, 3.35076e-06, 3.45384e-06, 3.34407e-06]
   print speedup(new, old, 1e-5)
   print speedup(old, new, 1e-5)