blob: 67852aaf982280e59bc82c27023d55ad9f912983 [file] [log] [blame]
Benjamin Petersonee8712c2008-05-20 21:35:26 +00001from test.support import TestFailed
Tim Peters7ae22292001-05-08 03:58:01 +00002
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
12PI = 3.14159265358979324
13TWOPI = 6.28318530717958648
14
15PI_str = "3.14159265358979324"
16TWOPI_str = "6.28318530717958648"
17
18# Verify that the double x is within a few bits of eval(x_str).
19def 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
29check_ok(PI, PI_str)
30check_ok(TWOPI, TWOPI_str)