[Python-checkins] CVS: python/dist/src/Lib/test test_math.py,1.5,1.6

[Tim Peters]

Update of /cvsroot/python/python/dist/src/Lib/test
In directory slayer.i.sourceforge.net:/tmp/cvs-serv13972/python/dist/src/Lib/test

Modified Files:
	test_math.py 
Log Message:
Stop raising OverflowError on underflows reported by libm (errno==ERANGE and
libm result is 0).  Cautiously add a few libm exception test cases:
1. That exp(-huge) returns 0 without exception.
2. That exp(+huge) triggers OverflowError.
3. That sqrt(-1) raises ValueError specifically (apparently under glibc linked
   with -lieee, it was raising OverflowError due to an accident of the way
   mathmodule.c's CHECK() macro happened to deal with Infs and NaNs under gcc).


Index: test_math.py
===================================================================
RCS file: /cvsroot/python/python/dist/src/Lib/test/test_math.py,v
retrieving revision 1.5
retrieving revision 1.6
diff -C2 -r1.5 -r1.6
*** test_math.py	2000/08/10 04:23:30	1.5
--- test_math.py	2000/10/12 06:10:24	1.6
***************
*** 153,154 ****
--- 153,183 ----
  testit('tanh(0)', math.tanh(0), 0)
  testit('tanh(1)+tanh(-1)', math.tanh(1)+math.tanh(-1), 0)
+ 
+ print 'exceptions'  # oooooh, *this* is a x-platform gamble!  good luck
+ 
+ try:
+     x = math.exp(-1000000000)
+ except:
+     # mathmodule.c is failing to weed out underflows from libm, or
+     # we've got an fp format with huge dynamic range
+     raise TestFailed("underflowing exp() should not have rasied an exception")
+ if x != 0:
+     raise TestFailed("underflowing exp() should have returned 0")
+ 
+ # If this fails, probably using a strict IEEE-754 conforming libm, and x
+ # is +Inf afterwards.  But Python wants overflows detected by default.
+ try:
+     x = math.exp(1000000000)
+ except OverflowError:
+     pass
+ else:
+     raise TestFailed("overflowing exp() didn't trigger OverflowError")
+ 
+ # If this fails, it could be a puzzle.  One odd possibility is that
+ # mathmodule.c's CHECK() macro is getting confused while comparing
+ # Inf (HUGE_VAL) to a NaN, and artificially setting errno to ERANGE
+ # as a result (and so raising OverflowError instead).
+ try:
+     x = math.sqrt(-1.0)
+ except ValueError:
+     pass