"Robert A Duff" <bobduff@world.std.com> wrote in message
news:wccvgm6bk7b.fsf@world.std.com...
> John English <je@brighton.ac.uk> writes:
>
> > Hmm, the "obvious" way to handle exceptions involves one extra word
> > in the stack frame (a pointer to the start of the exception handling
> > code) which costs (typically) 4 bytes per handled block and 1 extra
> > word to pop on exit, which may or may not cost nothing, but is certainly
> > pretty cheap.
>
> But the more desirable implementation is to save the small cost of
> setting that pointer, and spend perhaps 10,000 instructions searching a
> table of code addresses when an exception is raised.  If exceptions
> being raised are rare, but blocks protected by exception handlers are
> more common, that's a win.
>
> > Does anyone have any references to alternative ways of implementing
> > exception handling?
>
> One variant of the code-table technique was decribed in the Ada 83
> rationale.  The implementation you described above is essentially
> equivalent to the VAX/VMS standard method.  I don't have other
> references at hand, but surely a lot of this stuff is common lore, and
> documented somewhere.

T. P. Baker and G. A. Riccardi, �Implementing Ada Exceptions,� IEEE
Software, vol. 3, no. 5, pp. 42-51, 1986.