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IBM 7090 - Page 86

IBM 7090
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During
I
time
of
the
next
instruction,
the
AC
fraction
is
checked
for
zero
by
adding
one
to
the
l'
s
complement
of
the
fraction.
If
the
fraction
is
zero,
the
addition
will
cause
a
column
9
carry.
For
a
zero
AC
fraction,
the
whole
AC
is
set
to
zero
and
the
characteristic
of
the
MQ
is
left
at
zero.
If
the
AC
fraction
is
not
zero,
there
is
no
column
9
carry
and
the
MQ
characteristic
is
set
2710
less
than
the
AC
characteristic.
During
I
time
of
the
next
instruction,
the
AC
and
MQ
signs
are
set
to
the
algebraic
sign
of
the
pr
oduct.
Unnormalized
Floating
Multiply
UFM
-0260
(Min
I,
E)
(Max
I,
E,
11L)
This
instruction
multiplies
the
floating-point
number
stored
at
the
location
indicated
by
the
address
by
the
floating-point
number
in
the
MQ.
This
instruction
operates
the
same
as
FMP
except
that
the
result
is
not
normalized
or
tested.
The
minus
PR
(S)
pre-
vents
FP
normalizing
gate
(Systems
2.
10.24.
1).
The
PR
(S)
not
being
plus
prevents
the
reset
of
the
AC
during
the
following
I
cycle
(Systems
2.
10.25.1).
The
minus
PR
(S)
prevents
turning
on
the
FP
trigger
if
MQ =
0,
Systems
02.12.07.
O.
Floating
Round
FRN
+0760
...
0011(1, L)
Figure
5.3-25
This
instruction
examines
the
contents
of
MQ(9)
and
if
MQ(9)
contains
a
bit,
a
one
is
added
to
the
contents
of
the
AC. A
carry
out
of AC(9)
increases
the
characteristic
by
one,
causes
the
fraction
to
be
shifted
right,
and
a one
to
be
placed
in
AC(9).
Floating
Divide
or
Halt
FDH
+0240
(Min
I,
E,
L)
Figure
5.3
-26
(Max
I,
E,
12L)
This
instruction
divides
the
floating-point
number
placed
in
the
AC
by
the
floating-
point
number
stored
at
location
X.
The
result
is
a
floating-point
quotient
in
the
MQ
and
the
floating-point
remainder
of
the
dividend
in
the
AC.
The
sign
of
the
MQ
is
the
algebraic
sign
of
the
quotient.
The
sign
of
the
AC
is
the
sign
of
the
dividend.
The
characteristic
of
the
MQ
is
equal
to
the
characteristic
of
the
ACC
minus
the
character-
istic
of
the
SR,
increased
by
2008.
The
characteristic
of
the
remainder
is
2710
less
than
the
original
dividend
characteristic.
If
two
normalized
numbers
are
used
as
divisor
and
dividend
fractions,
the
dividend
fraction
cannot
be
twice
as
large
as
the
divisor
fraction.
Therefore,
the
7090
is
designated
to
halt
only
when
the
dividend
fraction
is
at
least
twice
as
large
as
the
divisor
fraction.
The
divide
check
indicator
is
turned
on
to
cause
the
halt.
The
contents
of
the
MQ
will
be
normal
zero
and
the
contents
of
the
ACC
will
remain
tulchanged.
A
zero
dividend
fraction
causes
the
division
to
be
skipped,
but
does
not
halt
the
computer.
A
normal
zero
quotient,
plus
remainder,
results.
If
the
initial
factors
are
normal
floating
point
numbers,
the
quotient
is
also
normal.
As
in
any
division
using
exponents,
the
fractions
are
divided
and
the
exponent
of
the
divisor
is
subtracted
from
the
exponent
of
the
dividend.
The
result
is
the
correct
quo-
tient
factor
and
exponent.
Division
of
the
fractions
is
done
in
the
same
manner
as
DVH,
by
shifting
left
and
attempting
reduction.
When
reduction
is
successful,
a
bit
is
put
into
MQ(35).
Only
2710
reductions
are
attempted
in
FDH
because
the
fraction
is
con-
tained
in
27
10
positions.
FDH
uses
an
E
cycle
and
several
L
cycles.
The
L
cycles
are
divided
into
three
types
(first,
second,
and
third
step)
through
use
of
the
tally
counter.
85

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