The parameter value
is
passed to the USR subroutine
in
system loca-
tions
that
function
as
a floating point accumulator (FAC) for ail functions. The
FAC resides
in
six bytes from memory locations
94
to
99
(5E
16-6316).
The
FAC has the following format:
O=positive
-1
=negative
(FAC
ating
nt)
99
9897
96
95
Fraction
Flo
1
1
Poi
11
Sign
!
Exponent
f
Memory location.
94
Like floating variables. the exponent
is
stored
in
excess
128
format
and
the
fraction
is
normalized
with
the
high-order bit
of
byte
95
(the high-order byte
of
the fraction) set to
1.
The difference between this
format
and the variable
format
is
that
the
high-order 1 bit
is
present
in
byte
95
of
the
FAC.
An extra byte (99)
is
used
to
hold the sign
of
the fraciton. (This
is
do
ne
for
ease
of
manipulation by
the
functions
that
use the
FAC.)
The USR subroutine must fetch the value passed to
it
from the FAC
locations.
It
must deposit the value being returned into the FAC before ter-
minating.
If
the USR subroutine does not alter the FAC, then the same value
is
returned to the program
as
was
passed from it.
333
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