Write an LMC program to let the user enter two numbers, num1 and num2.
The program should output the results of multiplying these two numbers: num1 x num2.
While checking the Little Man Computer Instruction Set (See table at the bottom of this post), you will have noticed that, through there are two instructions for adding (ADD) and subtracting (SUB) numbers, there is no instruction for multiplying two numbers.
The solution to overcome this, is two consider a multiplication as a series of additions. For instance:
This is how we will implement our multiplication algorithm:
INP STA NUM1 INP STA NUM2 LOOP LDA TOTAL ADD NUM1 STA TOTAL LDA NUM2 SUB ONE STA NUM2 BRP LOOP LDA TOTAL SUB NUM1 STA TOTAL OUT HLT NUM1 DAT NUM2 DAT ONE DAT 1 TOTAL DAT 0
LMC Instruction Set
Note that in the following table “xx” refers to a memory address (aka mailbox) in the RAM. The online LMC simulator has 100 different mailboxes in the RAM ranging from 00 to 99.
|INP||INPUT||Retrieve user input and stores it in the accumulator.||901|
|OUT||OUTPUT||Output the value stored in the accumulator.||902|
|LDA||LOAD||Load the Accumulator with the contents of the memory address given.||5xx|
|STA||STORE||Store the value in the Accumulator in the memory address given.||3xx|
|ADD||ADD||Add the contents of the memory address to the Accumulator||1xx|
|SUB||SUBTRACT||Subtract the contents of the memory address from the Accumulator||2xx|
|BRP||BRANCH IF POSITIVE||Branch/Jump to the address given if the Accumulator is zero or positive.||8xx|
|BRZ||BRANCH IF ZERO||Branch/Jump to the address given if the Accumulator is zero.||7xx|
|BRA||BRANCH ALWAYS||Branch/Jump to the address given.||6xx|
|HLT||HALT||Stop the code||000|
|DAT||DATA LOCATION||Used to associate a label to a free memory address. An optional value can also be used to be stored at the memory address.|