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If
the
application
program
is
able
to
release
any
memory
from
its
AMI
file,
it
should
do
so.
The
space
freed
will
always be taken
from the
end
of
the
file,
so
that
any
internal
data
structures
necessary should be
moved down
to
place the
free
memory
at
the
end
of
the
file.
The
application
program
should then
return
to
the
O/S
by doing an
IRET
instruction
and
return
in
AX
the
number
of
paragraphs
of
memory
actually
made
available
to
the
O/S
to
recover from
the
end
of
the
AMI
file.
If
no
memory was made
available,
AX
must
contain
0.
Any
changes
to
DS,
ES, SS,
or
SP
within
this
hook
routine
will
be
remembered
by
the
O/S
and
those
changed
registers
will
be
restored before returning
to
the application
when
the
O/S
function
call
completes.
If,
for
example,
the
application
program's
stack
were
at
the
end
of
the
AMI,
the
hook
routine
could
copy
the data
on
the stack
down
by
the
requested amount,
adjust
SP
to point
to
the
new
stack
location,
and
then perform
the
IRET.
HH
O/S
would
then
remember
the
new
location
of
the
application
program's
stack,
and
that
stack
would be
in
effect
when
the
interrupted function
call
completes.
HH
O/S
will
have pushed
some
critical
information
onto
the application
program's stack before
performing the
INT
44h
instruction.
For
this
reason, the
hook
routine
must
preserve the
contents
of
the stack,
although
it
is
allowed
to
move
its
location.
HH
O/S
is
not
reentrant.
For
this
reason, the
INT
44h hook
routine
may
not
make
any
HH
O/S
function
calls.
The
INT 44h hook
routine
is
allowed
to
perform
any
of
the
HH
O/S
interrupts
that
are
explicitly listed
as being
reentrant.
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