Question

Multiply with Little Man Computer

Asked by: scottdfreer

How do I multiply two positive numbers using "Little Man Computer" that does not have a multiply instruction? It only has add.

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Asked On
2007-09-18 at 09:47:54ID22836555
Tags

man

,

little

,

computer

Topics

Theory

,

Software/Systems Design

,

New Computer Users

Participating Experts
2
Points
150
Comments
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Answers

 

by: warrenbucklesPosted on 2007-09-18 at 09:59:46ID: 19914638

Multiplication is a form of addition: build a loop with one of the numbers as the index and add the other number to an accumulator the required number of times - make sure you get the index correct depending on how you initialize the accumulator (to zero or the number you are multiplying).

wb

 

by: scottdfreerPosted on 2007-09-18 at 10:30:33ID: 19914907

That is a good start, but I was hoping for a sample program, because I'm just not getting it. The simulator that I am using is called "Little Man Computer" and has 10 instructions. Read (reads the value input) , Print (sends the value in the register to the output tray) , Load (brings a number from memory storage back to the register) , Store (stores a number in the register to a designated memory location) , Stop, Add (adds the number in the register to a number from a given memory address) , Subtract (subtracts the number in the register from a number in a given memory address), Branch (jump to the designated address), BranchZ (If the value is zero, jump to the designated address), BranchP (If the value is positive, jump to the designated address). It only allows integers in the input tray, it has a maximum input of the value 499, and it has mailbox address locations 00 through 99.  Thank You, Scott

 

by: surajgupthaPosted on 2007-09-18 at 13:20:18ID: 19916261

Found this program at  http://povinelli.eece.mu.edu/teaching/coen030/lmc.html
add numbers in the IN basket. U can extend this to multiply

Label Instruction Comment
.LMC  ;A directive for the assembler
.LOOP READ ;Read in the next number
 BZ PRINTOUT ;If it's a zero, jump to printing
 ADD SUM ;If it's not a zero, add to sum
 STO SUM ;Remember to store the running sum
 B LOOP ;Go back to the beginning
.PRINTOUT LOAD SUM ;Place the sum in the calculator
 PRINT ;Print the calculator display
 STOP ;Give the Little Man a break
.DC SUM 000 ;Reserve a mailbox for SUM and initialize zero
.END  ;A directive for the assembler

 

by: warrenbucklesPosted on 2007-09-18 at 14:01:05ID: 19916540

Sounds like a mighty small sandbox, but I guess we all have to start somewhere.

surajguptha's fragment requires an input stream to control the program - the .LOOP READ line has the machine reading numbers, so a multiply would have to be setup like this:

5
5
5
5
0
This is, in effect, 5 * 4

However, it's not really multiplying - it's using an input stream to control an adder.

Maybe that's a semantic quibble, but I would assume a 'true' multiplication routine to take two operands and multiply them together, with an input stream as follows:

5
4


Where the two values read are the numbers to be multiplied.  You would read the first operand, put it (the  5) somewhere, read in the 4, stash it somewhere else, then use the location where you stored the 5 as your loop counter and decrement it each time you went through the loop, testing for zero to fall out of the loop.  The loop would add the location you stored the 4 to another location where your product would appear.  

Little sandboxes can be fun....

wb

.

20120131-EE-VQP-002

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