1 from test.test_support import TestFailed

     2 

     3 # A test for SF bug 422177:  manifest float constants varied way too much in

     4 # precision depending on whether Python was loading a module for the first

     5 # time, or reloading it from a precompiled .pyc.  The "expected" failure

     6 # mode is that when test_import imports this after all .pyc files have been

     7 # erased, it passes, but when test_import imports this from

     8 # double_const.pyc, it fails.  This indicates a woeful loss of precision in

     9 # the marshal format for doubles.  It's also possible that repr() doesn't

    10 # produce enough digits to get reasonable precision for this box.

    11 

    12 PI    = 3.14159265358979324

    13 TWOPI = 6.28318530717958648

    14 

    15 PI_str    = "3.14159265358979324"

    16 TWOPI_str = "6.28318530717958648"

    17 

    18 # Verify that the double x is within a few bits of eval(x_str).

    19 def check_ok(x, x_str):

    20     assert x > 0.0

    21     x2 = eval(x_str)

    22     assert x2 > 0.0

    23     diff = abs(x - x2)

    24     # If diff is no larger than 3 ULP (wrt x2), then diff/8 is no larger

    25     # than 0.375 ULP, so adding diff/8 to x2 should have no effect.

    26     if x2 + (diff / 8.) != x2:

    27         raise TestFailed("Manifest const %s lost too much precision " % x_str)

    28 

    29 check_ok(PI, PI_str)

    30 check_ok(TWOPI, TWOPI_str)