Little Man Virtual Machine

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A compiler + virtual machine to execute LMC assembly on your computer.

Executables

LMVM (virtual machine)

LMASM (assembler)

Mnemonics

Code	Mnemonic	Description
1xx	ADD	Add
2xx	SUB	Subtract
3xx	STA	Store into address
4xx		Unused
5xx	LDA	Load from address
6xx	BRA	Branch (always)
7xx	BRZ	Branch if zero
8xx	BRP	Branch if positive (or zero)
901	INP	Input
902	OUT	Output
000	HLT	Halt (coffee break)
	DAT	Data declaration
	;	Comment

All mnemonics are case-insensitive.

Addressing modes

Symbol	Description	Example	Definition of mode
(none)	Direct	ADD 5	Use the operand as an address to the value
LABEL	Direct (described by address/DAT at LABEL)	ADD fivevar	Use the operand as a label for the address to the value (as declared in a DAT statement)

Labels must consist of only Latin letters (abc...xyz), and are case-sensitive.

Warning The available memory addresses are 0-99 only. Any address outside of this range will cause an error.

Note In a DAT statement, the operand is an immediate value. If a label is passed, its address will be used as the value. It is the initial value of the variable.

Using labels

Labels can be used as branching points, or as a name for a memory space when used with the DAT operation.

Execution arguments

Assembler

The first positional argument is the input file to use as the entrypoint. It is required.
Additionally, these arguments are available:

Short arg	Long arg	Description
-o <file>	--output <file>	Output file, defaults to the same file name as the input (but with executable extension) in the current directory
-h	--help	Display help
-k	--no-overwrite	Keep the output file if it already exists. Refuses to overwrite.
-v	--version	Display version
-d	--debug	Enable debug mode
-x	--silent	Silent mode. Don't print anything to stdout or stderr.

Virtual machine

The first positional argument is the file to execute. It is required.
Additionally, these arguments are available:

Short arg	Long arg	Description
-h	--help	Display help
-v	--version	Display version
-d	--debug	Enable debug mode
-x	--silent	Silent mode. No output.

Example programs

Count to 5

; Count to 5

loop    LDA count  ; load the value of count into the accumulator
        ADD one
        OUT        ; output the value of the accumulator
        STA count  ; hold the value of the accumulator into count
        SUB five   ; subtract 5 from the accumulator...
        BRZ end    ; ...to therefore stop execution if the count is 5 (ACC=0)
        BRA loop   ; else, branch to loop
end     HLT
        
        
count   DAT 0
one     DAT 1
five    DAT 5

Doubler

; Program to safely double the user input without erroring

entry	    INP		    ; get user input

	    BRP	check	; check not negative
	    BRA	entry

; therefore the value is >= 0
check       SUB	max	    ; check if will exceed max allowed
            SUB	one
	    BRP	entry
	    ADD	one	    ; revert subtraction for range check
	    ADD	max

; therefore the value is within 0-999, so can be safely STA'd to double
	    STA	tmp
	    ADD	tmp
	    OUT
	    BRA	entry

tmp         DAT 0
one	    DAT	1
max	    DAT	999

Building from source

You need CMake 3, and a C compiler. GCC is recommended (through MINGW on Windows).
For installers, you need CMake 3.20 or later.
You also need pandoc if you want to generate installers.
Windows may also install NSIS if you want to generate an NSIS installer.

1. Clone the repository: git clone https://github.com/obfuscatedgenerated/LMVM.git
2. Change directory: cd LMVM
3. Create a build directory: mkdir build
4. Change directory: cd build
5. Run CMake generation: cmake .. (you can force a specific generator with the -G <generator> option, enable release mode with -DCMAKE_BUILD_TYPE=Release)
   By default, CPack installer data will be generated. This requires pandoc to be installed. To disable installer generation, pass -DINSTALLER=OFF to CMake.
6. Build the project: cmake --build . (you can specify a specific target with the --target <target> option)
7. Optional: create installers with CPack: cpack (you can specify a specific generator with the -G <generator> option, enable release mode with -C Release)