Author: rgrjr
Date: Sat Jan 5 19:32:44 2008
New Revision: 24577
Modified:
trunk/docs/pdds/pdd03_calling_conventions.pod
Log:
+ Expand description of current overflow/underflow behavior, explain
how to control this via C<errorson>. Documentation deficit pointed
out by bgeron.
Modified: trunk/docs/pdds/pdd03_calling_conventions.pod
==============================================================================
--- trunk/docs/pdds/pdd03_calling_conventions.pod (original)
+++ trunk/docs/pdds/pdd03_calling_conventions.pod Sat Jan 5 19:32:44 2008
@@ -218,20 +218,27 @@
=back
-=head3 Overflow
+=head3 Overflow and underflow
-If too many values are provided to fit into the given target registers, Parrot
-will throw an exception. Note that if the final target is a P register with
-FLAT set, then this exception can never occur.
+If too many or too few values are provided for the given target registers,
+Parrot by default will throw an exception for C<get_params>, but not for
+C<get_results>. This error behavior can be controlled via the C<errorson> and
+C<errorsoff> opcodes using C<PARROT_ERRORS_PARAM_COUNT_FLAG> for C<get_params>
+and C<PARROT_ERRORS_RESULT_COUNT_FLAG> for C<get_results>. (It is not
+possible to control underflow behavior separately from overflow.)
+
+Note that if the final target is a P register with FLAT set, then overflow can
+never occur. Similarly, if all target registers are marked B<OPTIONAL>, then
+underflow is impossible.
+
+Note also that when these errors are off, any excess destination registers in
+the case of underflow are left untouched, rather than being reset to zero or
+null. Excess registers explicitly marked B<OPTIONAL> are always reset,
+regardless of the error flag settings.
RT#45357 - which exception? We really could use an exception subsystem.
Oh, wait, that's my job. Never mind. --Chip
-=head3 Underflow
-
-If too few values are provided so that some target registers are left unset,
-this too results in an exception.
-
=head3 Ordering of named values (outgoing)
Named values (arguments, or values to return) must be listed textually after
