Algorithms

Below are some helpful comparisons between different ways of acheiving the same result, starting from design, move on to high-level language, into low-level language and finally machine code.

This guide was originally intended to help with LMC implementation, but is also useful for general python deisgn/coding.

Comparison

Topic FlowChart PseudoCode Python Assembler Machine Code
Assigning a variable Assignment a ← 5 a=5 a DAT 5
Input Input a ← USERINPUT a=input() INP
STA a		 901
3xx
Output Output a ← 5 a=5 LDA a
OUT		 5xx
902
Subtraction Subtraction a ← b - c a=b-c LDA b
SUB c
STA a		 5xx
2xx
3xx
Selection:
Greater than		 Selection-GT IF a > b THEN
 funcA()
ELSE
 funcB()
ENDIF		 a > b:
 funcA()
else:
 funcB()		 LDA b
SUB a
BRP funcA
BRA funB		 5xx
2xx
8xx
6xx
Selection:
Less than		 Selection-LT IF a < b THEN
 funcA()
ELSE
 funcB()
ENDIF		 a < b:
 funcA()
else:
 funcB()		 LDA a
SUB b
BRP funcB
BRA funcA		 5xx
2xx
8xx
6xx
Selection:
Equal to		 Selection-EQ IF a = b THEN
 funcA()
ELSE
 funcB()
ENDIF		 if a == b:
 funcA()
else:
 funcB()		 LDA a
SUB b
BRZ funcA
BRA funcB		 5xx
2xx
7xx
6xx
Selection:
Not equal to		 Selection-NEQ IF a ≠ b THEN
 funcA()
ELSE
 funcB()
ENDIF		 if a ≠ b:
 funcA()
else:
 funcB()		 LDA a
SUB b
BRZ funcB
BRA funcA		 5xx
2xx
7xx
6xx
Iteration:
While loop		 Iteration-WHILE WHILE a ≠ b
 OUTPUT b
 a ← USERINPUT
ENDWHILE		 while a != b:
 print(b)
 a = input()		 while LDA a
  SUB b
  BRZ endwhile
  LDA b
  OUT
  INPU
  STA a
  BRA while
endwhile HLT
a DAT 0
b DAT 5		 5xx
2xx
7xx
5xx
902
901
3xx
6xx
000
Iteration:
For loop (count-up)		 Iteration-FOR_UP FOR i ← 0 TO 9
 OUTPUT i
ENDFOR		 for i in range(10):
 print(i)		 for LDA i
  OUT
  ADD one
  STA i
  SUB ten
  BRZ endfor
  BRA for
endfor HLT
i DAT 0
one DAT 1
ten DAT 10		 5xx
902
1xx
3xx
2xx
7xx
6xx
000
Iteration:
For loop (count-down)		 Iteration-FOR_DOWN FOR 1 ← 10 TO 1
 OUTPUT i
ENDFOR		 for i in range(10, 0, -1):
 print(i)		 for LDA i
  OUT
  SUB one
  STA i
  BRZ endfor
  BRA for
endfor HLT
1 DAT 10
one DAT 1		 5xx
902
2xx
3xx
7xx
6xx
000

Some useful links for both LMC & Pseudocode.

  1. Online LMC
  2. LMC Explanation
  3. PseudoCode CheatSheet
  4. PseudoWars
  5. AQA PseudoCode Guidelines

LMC Instructions

Simple explanations for the various LMC commands.

Instructions Mneumonic Machine Code Explanation
Add ADD 1xx Adds the contents of memory xx to the ACCUMULATOR.
Subtract SUB 2xx Subtracts the contents of memory xx from the ACCUMULATOR.
Store STA 3xx Copies the contents of the ACCUMULATOR to memory xx.
Load LDA 5xx Copies the contents of memory xx to the ACCUMULATOR.
Branch ALWAYS BRA 6xx Always set the program counter to xx. The program continues from the instruction at memory xx.
Branch if ZERO BRZ 7xx Set the program counter to xx only of the ACCUMULATOR is zero.
Branch if POSITIVE BRP 8xx Set the program counter to xx only if the ACCUMULATOR is zero or positive (greater than zero).
Input INP 901 Copy the contents of the INBOX to the ACCUMULATOR.
Output OUT 902 Copy the contents of the ACCUMULATOR to the OUTBOX.
Define Variable DAT Reserves this memory slot as a variable, settinmg its contents to the value specified.
Halt HLT 000 Halts execution of the program.