IBM 1620 1 Manual page 22

2. The Load Dividend instruction,
28 00099 00650,
causes the low-order position of the dividend
to be placed at 00099. The sign (plus) is stored
at 00099.
3. The Load Dividend Immediate instruction,
18 00098 00650,
causes the low-order position of the dividend
(the Q part of the instruction) to be placed in
the field beginning at 00098. The sign (plus) is
stored at 00099.
Execution Time. T
==
400 +40Dn fLsec, where
Dn equals the number of digits in the dividend.
Load Dividend Immediate (LDM-l 8)
Description. The description for Load Dividend
applies except that the data in the Q part of the
instruction is transmitted to the P address.
Execution Time.
Same as a Load Dividend
(LD-28).
Divide (0-29)
Description. The divisor (Q address) is successive-
ly subtracted from the dividend. The P address of the
Divide instruction positions the divisor for the first
subtraction from the high-order positions of the divi-
dend, as in manual division. The P address is deter-
mined by subtracting the number of digits in the
quotient from 100.
Examples: Problem 1: 4906
+-
23
==
0213 and a
remainder of 07. Figure 15 shows the manner in which
the 1620 solves this problem.
Problem 2: -212 (212)
+-
24
==
-8.83 (00883) and
a remainder of
08.
Figure 16 shows how the 1620
solves this problem.
As illustrated in these examples, each subtraction
without overdraw causes the quotient digit to be
increased by 1. Quotient digits are developed in the
units position of the Multiplier/Quotient register. An
overdraw initiates a correction cycle (the divisor is
added once), and the next subtraction occurs one
place to the right.
The first (high-order) quotient digit is stored at
the address equal to the P address of the Divide in-
struction minus the length of the divisor. A Hag bit
is generated and stored with the first quotient digit.
Subsequent quotient digits are stored to the right of
the last-stored quotient digit. Division is terminated
18
after the last quotient digit is developed by sub-
tractions with the units position of the divisor at
00099.
The quotient and remainder replace the dividend
in the product area. The address of the quotient is
00099 minus the length of the divisor. The algebraic
sign of the quotient (determined by the sign of the
dividend and divisor) is automatically placed in the
low-order position of the quotient. The address of the
remainder is 00099. A Hag bit is automatically placed
in the high-order position. The remainder has the sign
of the dividend and the same number of digits as the
divisor.
The
H/P
indicator is on if the quotient is positive
and not zero; the
E/Z
is on if the quotient is zero.
N either indicator is on if the quotient is negative.
The quotient must be at least two digits in length;
one position is required for the sign and one for the
field mark (Hag bit).
Execution Time. T
==
160
+
520DvQt
+
740 Qt
fLsec. Dv and Qt equal the number of digits in the
divisor and quotient, respectively. The formula as-
sumes an average quotient digit of 4.5. If a Load
Dividend or Load Dividend Immediate instruction
is used, the divide operation execution time may be
considered as the total time for both the Load Divi-
dend and Divide instructions.
T
==
560
+
40Dn
+
520DvQt
+
740Qt
fLsec
Divide Immediate CDM-19J
Description. The description of Divide (D-29) ap-
plies except that the data in the Q part of the in-
struction is used as the divisor.
Execution Time. Same as Divide (D-29).
Decimal Point Location
The computer is unaware of decimal points, except
for Automatic Floating-Point operations (special
feature). Decimal point location for any given divide
calculation is easily determined by simply subtracting
the number of decimal digits in the divisor from the
number of deCimal digits in the dividend. The result
is the number of decimal digits in the quotient. For
example, if the divisor and dividend values in Problem
2 (Figure 16) are 2.4 and 21.200, the quotient value is
008.83 (3 - 1
==
2). Note that the original dividend
21.4, became 21.400 as a result of its placement by
the Load Dividend instruction. Thus, the number
of dividend decimal digits must include the zeros
to the right of the loaded dividend.