Re: [Chicken-hackers] [PATCH] Fix for #989 and hopefully #877 too

[Peter Bex]

On Wed, Nov 06, 2013 at 06:00:34PM +0100, "Jörg F. Wittenberger" wrote:
> Now I cam confused.
> 
> True, there are 256 possible signal handlers in ##sys#signal-vector
> How could those be addressed/used at all?

The timer interrupt signal has value 255.  I'm sure there must be UNIXen
out there which use nonstandard signals of higher numbers than 32.
For example, the Linux signal(7) manual on the box which serves
call-cc.org mentions that there are real-time signals which are numbered
33 through 64.

> >   The manpage for
> >signal(7) on my NetBSD box shows 32 signals.  That means the pending 
> >signals
> >won't ever fit in a fixnum on a 32-bit machine.
> 
> You're right: somehow it seems to have escaped me that attaching the 
> type tag on the way from C to Scheme would reduce the number of bits 
> avail.  (Otherwise I've been working from my "sure knowledge" that there 
> are only 32 signals, which in turn would fit into a single word.)

It could be worse, you could be losing one more bit, depending on what
happens to the sign bit when you're shifting unsigned signal numbers
into a signed signal bitmask (how this stuff is defined in the C spec
confuses me no end).

Cheers,
Peter
-- 
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