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| -rw-r--r-- | Lib/test/double_const.py | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/Lib/test/double_const.py b/Lib/test/double_const.py new file mode 100644 index 0000000..5ea6de0 --- /dev/null +++ b/Lib/test/double_const.py @@ -0,0 +1,30 @@ +from test_support import TestFailed + +# A test for SF bug 422177: manifest float constants varied way too much in +# precision depending on whether Python was loading a module for the first +# time, or reloading it from a precompiled .pyc. The "expected" failure +# mode is that when test_import imports this after all .pyc files have been +# erased, it passes, but when test_import imports this from +# double_const.pyc, it fails. This indicates a woeful loss of precision in +# the marshal format for doubles. It's also possible that repr() doesn't +# produce enough digits to get reasonable precision for this box. + +PI = 3.14159265358979324 +TWOPI = 6.28318530717958648 + +PI_str = "3.14159265358979324" +TWOPI_str = "6.28318530717958648" + +# Verify that the double x is within a few bits of eval(x_str). +def check_ok(x, x_str): + assert x > 0.0 + x2 = eval(x_str) + assert x2 > 0.0 + diff = abs(x - x2) + # If diff is no larger than 3 ULP (wrt x2), then diff/8 is no larger + # than 0.375 ULP, so adding diff/8 to x2 should have no effect. + if x2 + (diff / 8.) != x2: + raise TestFailed("Manifest const %s lost too much precision " % x_str) + +check_ok(PI, PI_str) +check_ok(TWOPI, TWOPI_str) |