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* libguile/numbers.c (scm_product): Handle exact 0 differently. A product containing an exact 0 now returns an exact 0 if and only if the other arguments are all exact. An inexact zero is returned if and only if the other arguments are all finite but not all exact. If an infinite or NaN value is present, a NaN value is returned. Previously, any product containing an exact 0 yielded an exact 0, regardless of the other arguments. A note on the rationale for (* 0 0.0) returning 0.0 and not exact 0: The exactness propagation rules allow us to return an exact result in the presence of inexact arguments only if the values of the inexact arguments do not affect the result. In this case, the value of the inexact argument _does_ affect the result, because an infinite or NaN value causes the result to be a NaN. A note on the rationale for (* 0 +inf.0) being a NaN and not exact 0: The R6RS requires that (/ 0 0.0) return a NaN value, and that (/ 0.0) return +inf.0. We would like (/ x y) to be the same as (* x (/ y)), and in particular, for (/ 0 0.0) to be the same as (* 0 (/ 0.0)), which reduces to (* 0 +inf.0). Therefore (* 0 +inf.0) should return a NaN. * test-suite/tests/numbers.test: Add many multiplication tests. * NEWS: Add NEWS entry. |
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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.