Reformat and add a comment

support/compute-powers.py

@@ -39,7 +39,7 @@ for i, exp in enumerate(range(min_exponent, max_exponent + 1, step)):
 
 print('Significands:', end='')
 for i, fp in enumerate(powers):
-    if i % 4 == 0:
+    if i % 3 == 0:
         print(end='\n ')
     print(' {:0<#16x}'.format(fp.f, ), end=',')