[TUHS] undiagnosed pic error

Douglas McIlroy douglas.mcilroy at dartmouth.edu
Sun Jun 18 01:59:37 AEST 2023

Google claims I just sent another unintended reply, this time unfinished.


On Wed, Jun 14, 2023 at 6:42 AM Marc Donner <marc.donner at gmail.com> wrote:
> How sparse is the 35x35 matrix?  For comprehensibility would it be the best way to do it?
> On Tue, Jun 13, 2023 at 9:59 PM Douglas McIlroy <douglas.mcilroy at dartmouth.edu> wrote:
>> There may be a simple generic way to correct pic's habit of accepting
>> any set of object modifiers on any object, but obeying only a
>> compatible subset.
>> Pic already collects a bit vector of modifier types attached to the
>> current object. If that were extended with a few more bits that
>> designate the object types, the size, B, of the bit vector would be
>> about 35--an easy fit in one 64-bit word. Then a BxB bit matrix could
>> record both modifier/modifier incompatibilities and object/modifier
>> incompatibilities. The collected bit vector needs to be tested against
>> the matrix once per object definition.
>> It seems to be harder to catch duplication of modifiers, requiring
>> extra code at all points where bits are set. Nevertheless, this kind
>> of error also merits detection.
>> Some questions
>> Does anybody think the issue is not worth addressing?
>> Is there a better scheme than that suggested above?
>> Is the scheme adequate? It would not, for example, catch a three-way
>> incompatibility that does not entail any pairwise incompatibility,
>> should such an incompatibility exist.
>> Any other thoughts?
>> Doug
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