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Mark H Weaver 9448a078b5 Fix 'round-ash' of negative integers by huge right shift counts. 
This is a followup to commit 011aec7e24.

When rounding, right shifting a negative integer by a huge shift count
results in 0, not -1.

* libguile/numbers.c: Add top-level 'verify' to ensure that the
assumptions in 'scm_ash' and 'scm_round_ash' are valid.
(scm_round_ash): In the case that handles huge right shifts, require
that the shift count _exceeds_ the integer length, and return 0 instead
of -1.
* test-suite/tests/numbers.test: Adjust tests accordingly.
2018-10-14 05:35:50 -04:00
..
lalr remove duplicate when/unless definitions 2012-01-20 21:16:50 +01:00
standalone On Hurd, skip tests that require working setrlimits for memory 2017-05-16 21:44:04 +02:00
test-suite iprin1 uses scm_c_put_string 2016-05-30 15:07:23 +02:00
tests Fix 'round-ash' of negative integers by huge right shift counts. 2018-10-14 05:35:50 -04:00
vm Rename "RTL" to "bytecode" 2013-12-02 21:31:47 +01:00
ChangeLog-2008 Rename ChangeLog' files to ChangeLog-2008'. 2008-09-12 21:49:58 +02:00
guile-test Minor expansion of guile-test comments 2017-03-01 10:40:52 +01:00
Makefile.am tests: Add SRFI-71 test. 2018-06-18 14:14:47 +02:00
README Revert "Note need for subscription to bug-guile@gnu.org." 2008-12-10 19:07:14 +00:00

README 

This directory contains some tests for Guile, and some generic test
support code.

To run these tests, you will need a version of Guile more recent than
15 Feb 1999 --- the tests use the (ice-9 and-let*) and (ice-9
getopt-long) modules, which were added to Guile around then.

For information about how to run the test suite, read the usage
instructions in the comments at the top of the guile-test script.

You can reference the file `lib.scm' from your own code as the module
(test-suite lib); it also has comments at the top and before each
function explaining what's going on.

Please write more Guile tests, and send them to bug-guile@gnu.org.
We'll merge them into the distribution.  All test suites must be
licensed for our use under the GPL, but I don't think I'm going to
collect assignment papers for them.



Some test suite philosophy:

GDB has an extensive test suite --- around 6300 tests.  Every time the
test suite catches a bug, it's great.

GDB is so complicated that folks are often unable to get a solid
understanding of the code before making a change --- we just don't
have time.  You'll see people say things like, "Here's a fix for X; it
doesn't cause any regressions."  The subtext is, I made a change that
looks reasonable, and the test suite didn't complain, so it must be
okay.

I think this is terrible, because it suggests that the writer is using
the test suite as a substitute for having a rock-solid explanation of
why their changes are correct.  The problem is that any test suite is
woefully incomplete.  Diligent reasoning about code can catch corner
conditions or limitations that no test suite will ever find.



Jim's rule for test suites:

Every test suite failure should be a complete, mysterious surprise,
never a possibility you were prepared for.  Any other attitude
indicates that you're using the test suite as a crutch, which you need
only because your understanding is weak.