IBM 1620 1 Manual page 29

Core Storage Locations Core Storage Locotions
01590_01599
Instruction
01590---01599
Before After
~
I Ep I
I'v'q
I Eq
OP
I
P
I
Q
~ I Ep I
I'v'q
I Eq
1 2 310 217 8 91 0 1
o
110 1 5 9 410 1 5 9 9 2 0 110 217 8 910 1
Figure 20. Mq Shifted Right to Align Decimal Points
of d is less than L, M p is shifted
I
d
I
positions to
the right before Mq is added to Mp. The number of
low-order digits of Mp equal to
I
d
I
are truncated
as the shift is made. Eq replaces Ep (Figure 21).
If d is plus and equal to or larger than L, Mp is
above the range of Mq and no addition is performed
(Figure 22). If d is less than zero and
I
d
I
is equal
to or greater than L, Mq is above the range of Mp,
and no addition is performed. Mq replaces Mp,
and Eq replaces Ep (Figure 23).
Core Storage Locations Core Storage Locations
01590_01599
Instruct ion
01590---01599
Before After
~
I
Ep
I
I'v'q
I Eq
OP
I
P
I
Q
~
I Ep I
I'v'q
I Eq
1
2 310 117 8 910 2
o
110 1 5 9 410 1 5 9 9
"8
0 110 217 8 910 2
Figure 21. Mp Shifted Right to Align Decimal Points
Core Storage Locations Core Storage Locations
01590_01599
Instruction
01590--01599
Before After
~
I Ep I
I'v'q
I Eq
OP
I
P
I
Q
~
I Ep I
I'v'q
I Eq
1
2 310 517 8 91 Q 2
o
110 1 5 9 410 1 5 9 9 12
3ji.i
517 8 910 2
Figure 22. Mp Above Range of Mq
Core Storage Locations Core Storage Locations
01590_01599
Instruction
01590--01599
Before After
~
I
Ep
I
I'v'q
I
Eq
OP
I
P
I
Q
~
I Ep I
I'v'q
I Eq
1
2 3/,0 117 8 910 3
o
110 1 5 9 410 1 5 9 9 7 8 910 317 8 910 3
Figure 23. Mq Above Range of Mp
After addition has been completed, the number
of Mp digits is checked to determine if it exceeds L.
If so, this is an overflow condition; the low-order
digit of Mp is truncated, and the mantissa is shifted
one position to the right. A one is entered in the
high-order position of the mantissa, and a one is
added to Ep (Figure 24). When an overflow does
Core Storage Locations Core Storage Locations
0 1 5 9 0 - 01S99
Instruction
01590 _ _ _ 01599
Before After
~
IEpl1'v'q IEq
OP
I
P
I
Q
~ I Ep I
I'v'q
I Eq
9 8.710 414 5 610 4
o
110 1 5 9 410 1 5 9 9 1441051456104
Figure 24. Mantissa Overflow, Number Normalized
not exist, M p is scanned for zeros beginning with
the high-order position. High-order zeros are counted
(z), and Mp is shifted z positions to the left; va-
cated positions are set to zeros. Flag bits in Mp
are not altered or moved. Eq - z replaces Ep (Figure
25).
Core Storage Locations Core Storage Locations
01590_01599
Instruction
01590-_01599
Before After
~
I Ep I
I'v'q
I
Eq
OP
I
P
I
Q
~
I Ep I
I'v'q
I Eq
1 2 310 111 1 910 1
o
110 1 5 9 410 1 5 9 9 4 0 010
Iii
1 910 1
Figure 25. High-Order Zeros, Number Normalized
Execution Time. T (average)
==
400
+
l00L ILsec.
If the result is recomplemented, add 80L ILsec.
Floating Subtract (FSUB-021
Description. The floating subtract operation is the
same as the floating add operation except that sign
control procedures for Mq are reversed.
Execution Time. Same as Floating Add (F ADD-Ol ).
Floating Multiply (FMUL-031
Description. Mp is multiplied by Mq, and the
result replaces Mp. Ep is added to Eq, and the sum
replaces Ep. Mp and Ep are normalized, as required,
after multiplication. Mq and Eq are not altered in
core storage. The product is formed in the product
area, beginning at 00099 and extending through
lower-numbered core storage positionS to 00100
- 2L. The product area, 00080-00099, is cleared auto-
matically prior to multiplication. If L is greater than
10, the program must provide for clearing positions
00100 - 2L through 00079. After multiplication, the
digit at position--00l00 - 2L is tested for zero. If
the digit is other than a zero, the field at 00099 - L
replaces Mp (Figure 26). If the digit tested is a zero,
the field at 00100 - L replaces Mp and Ep
+
Eq
- 1 replaces Ep (Figure 27).
25