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IBM 7090 - Page 64

IBM 7090
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Note
that
three
additions
can
be
done
during
each
cycle
of
MPY.
The
maximum
num-
ber
of
shifts
during
an
L
cycle
can
be
12,
depending
on
positions
(34)
and
(35)
of
the
MQ.
Maximum
number
of
machine
cycles
required
for
MPY
is
14;
minimum
is
two.
Multiply
and
Round
MPR
-0200
(Min
I,
E)
Figure
5.3-18
(Max
I,
E,
12L)
This
instruction
executes
a
multiplication
followed
by
rounding
the
AC
contents.
The
multiplication
is
identical
to
MPY~
the
rounding
is
accomplished
by
adding
one
to
AC
(35)
if
MQ(l)
contains
a
one.
Variable-Length
Multiply
VLM
+0204
(Min
I,
E)
Figure
5.3-19
(Max
I,
E,
12L)
This
instruction
operates
much
the
same
as
MPY,
except
that
the
number
of
multi-
plier
positions
to
be
tested
is
specified
by
a
number
in
the
decrement
portion
of
the
instruc-
tion.
The
difference
between
MPY
and
VLM
occurs
in
the
E
cycle.
A
count
from
the
decrement
portion
of
the
instruction
is
put
into
the
SC
rather
than
438.
Usually
this
count
will
be
less
than
438.
A
count
of
608
or
greater
will
cause
an
I/A
cycle,
and
the
count
field
(12-17)
will
OR
with
12-17
of
the
IA
word.
Divide
or
Halt
DVH
+
0220
(Min
I,
E,
L)
(Max
I,
E,
12L)
Figure
5.3-20
This
instruction
divides
the
contents
of
the
AC
and
MQ,
taken
together
as
the
dividend,
by
the
word
stored
at
the
location
specified
by
the
address.
A
35-position
quotient
is
developed
in
the
MQ,
and
the
remainder
of
the
dividend
is
left
in
the
AC.
The
sign
of
the
MQ
is
set
to
the
algebraic
sign
of
the
quotient,
as
determined
by
the
SR
and
AC
signs.
The
sign
of
the
remainder
remains
the
same
as
the
sign
of
the
dividend.
The
size
of
the
registers
restricts
the
size
of
the
factors
to
be
divided.
If
the
AC
portion
of
the
dividend
were
greater
than
or
equal
to
the
divisor,
the
quotient
would
be
too
large
for
the
MQ.
In
this
case,
division
cannot
take
place,
and
the
computer
is
stopped
with
the
divide
check
indicator
on.
The
following
demonstrates
binary
division:
0110
Quotient
(MQ)
1011
J
1000010
Dividend
(AC
and
MQ)
1011
01011
1011
00000
0000
0000
Remainder
(AC)
Note
that
the
divisor
will
go
once
or
not
at
all
into
the
high
order
positions
of
the
dividend.
Therefore,
it
is
only
necessary
to
determine
if
the
divisor
is
equal
to
or
smaller
than
these
positions
of
the
dividend.
If
the
divisor
is
equal
to
or
smaller
than
the
selected
positions
of
the
dividend,
a
one
is
put
in
the
quotient
and
the
divisor
is
subtracted
from
that
portion
of
the
dividend.
If
the
divisor
is
larger
than
the
selected
portion
of
the
dividend,
a
zero
remains
in
the
quotient.
Another
position
of
the
dividend
is
now
taken
into
account,
and
the
procedure
starts
again.
This
continues
until
all
posi-
tions
in
the
dividend
have
been
used.
In
the
7090,
the
SR
and
AC
are
complement
added
to
determine
if
a
reduction
of
the
high
order
positions
of
the
dividend
is
possible.
If
the
reduction
is
possible,
these
63

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