| Benjamin Peterson | ee8712c | 2008-05-20 21:35:26 +0000 | [diff] [blame] | 1 | from test.support import TestFailed |
| Tim Peters | 7ae2229 | 2001-05-08 03:58:01 +0000 | [diff] [blame] | 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) |