Viewing file:  double_const.py (1.18 KB) -rw-r--r--
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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)
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