IBM 1620 1 Manual page 25

Incorrect D;v;sor Pos;t;on;ng
The following error conditions are caused by an in-
correct P address in the Divide instruction:
Overflow. As illustrated in Figure 17, an incorrectly
positioned divisor can cause more than nine success-
ful subtractions and an incorrect quotient. The divide
operation is terminated, the Arithmetic Check indi-
cator and light are turned on, but processing does
not stop unless the Overflow Check switch is set to
STOP.
Note the absence of a field-length flag in posi-
tion 00095 when division is terminated. The flag is
not placed automatically because the first quotient
digit, which normally causes the flag bit to be gener-
ated and stored, is not achieved.
If, after a division overflow, the field remaining in
the product area is to be used for further operations,
I nstruct ion
Description
D 29 00097.00650
Successful subtraction No.1
" " No.2
" " No. 3
" " No.4
" " No.5·
" "
No.6
" "
No.7
"
"
No.8
'.
" "
No.9
11
" No. 10
Figure 17. Divide Overflow
the program must provide for a flag to be set in the
desired position.
Loss of One or More High-Order Digits of the
Dividend. The high-order digit of the dividend is
assumed by the 1620 to be one position to the left
of the high-order digit of the divisor. Figure 18 shows
how the high-order digits of the dividend are lost
if the di"isor is positioned too far to the right. Proc-
essing continues with no indication of an incorrect
quotient.
I ncorrect Termination. If the P address is less than
10000, i.e., between 00100 and 09999, the divide op-
eration will terminate when a subtraction occurs at
OXX99. This, in effect, restricts the size of the divi-
dend to 10,020 digits, if only 20,000 positions of
core storage are installed.
0 -
"1M
~I.t')
-or-....
coO-
00650
0-0- 0-0- 0-0- 0-0- 0- 0-
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
2 1 0 0 0 0 0 2 1 2 0 0
-
2
1
1 9 1
-
2 1
1 7 0
-
2 1
1 4 9
-
2 1
1 2 8
-
2
1
1 0 7
-
2 1
0 8 6
-
2 1
0 6 5
-
2 1
0 4 4
-
2 1
0 2
3
-
2 1
0 0 0 0 0 0 0
2
0
0
21