Automatic Division - IBM 1620 1 Manual

The Automatic Division special feature simplifies
programming and increases the processing speed of
division problems by two to four times that of pro-
grammed routines. Only one command need be given.
Four commands are provided, however, to facilitate
positioning of the dividend and divisor in core stor-
age. There are no practical limitations placed upon
the size of the dividend. divisor, or quotient.
A quotient and remainder of 20 digits are devel-
oped in the product area (00080-00099). When the
quotient plus the remainder exceeds 20 digits, core
storage positions lower than 00080 ( 00079, 00078,
etc.) must be reset to zeros by programming. One
additional position should also be cleared to allow
for a possible overdraw. For example, if 25 positions
ary required for the quotient and remainder, 00074-
00079 would have to be reset to zeros before the
divide command was given.
The four instructions provided with the Divide
feature are:
Load Dividend (LD-28)
Load Dividend Immediate (LDM-18)
Divide (D-29)
Divide Immediate (DM-19)
The formula for computing the total execution
time follows the description of each instruction.
Data at Core
Instruction
Storage Address
Description
00650
(1) 28 00096 00650
21365
Load Dividend
(2) 28 00099 00650
01234 Load Dividend
(3) 18 00098 00650 56789 Load Dividend Immediate
Figure 14. Load Dividend Instructions
Automatic Division
Load Dividend (LD-281
Description. The dividend must be stored in the
product area before a Divide command is given.
The Load Dividend instruction may be used to satisfy
this requirement.
The product area (00080-00099) is automatically
reset to zeros. The dividend (Q address) is transmit-
ted to the product area (P address), beginning at the
low-order dividend digit and terminating at the flag
bit marking the high-order· position of the dividend
field. The P address is 00099 minus the number of
zero positions desired to the right of the dividend.
The algabraic sign of the dividend is automatically
placed in location 00099 regardless of where the low-
order dividend digit is placed by the P address. A
flag bit automatically marks the high-order digit of
the dividend.
Example: Two Load Dividend instructions and one
Load Dividend Immediate instruction are shown in
Figure 14.
0
00
0
0
0
0
0
0
1. The Load Dividend instruction,
, 28 00096 00650
causes the low-order position of the dividend to
be placed at 00096. The sign (minus) is stored
at 00099.
~ N
N C") "<t
l() -.0
r--..
00 0-
00 00 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
o
0
0 0 0
0
0 0
0
0
0 0
·
...
2 1 3 6 5
o
0
0
0 0
·
...
0 0 0 0 1 2 3 4
0 0
· ...
0 0 0 0 6 5 0 0
17