desmos-computer

What is this?

• a client-server architecture for synchronizing a file containing Desmos expressions to a graph, (cli/lib/server.py and cli/lib/clientside.py)
• an instruction set architecture for Turing machines whose cells contain IEEE 754 compliant integers in each cell, (cli/data/computer.py)
• an assembler for that instruction set architecture, (not yet!)
• and other utilities. (disassembler, etc.)

How does the ISA work?

The 'CPU', implemented in Desmos, takes in a list (aka an array, Turing tape, etc.) and starts execution at cell 1 (lists have 1-based indexes in Desmos). The list also serves as the memory, as well. (Think like Befunge's p command.)

Todo: disconnect opcode definitions and opcodes from the actual CPU implementation. Because of this, don't rely on this table! Check the implementation in data/computer.desmos.

Instruction mnemonic	Behavior	First parameter	Second parameter	Third parameter
jmp	Modify the instruction pointer and continue execution at the new location.	New instruction pointer	n/a	n/a
add	Take the values in addresses a and b and add them; store the result in address c.	address a	address b	address c
sub	See add instruction.	ld.	ld.	ld.
div	See add instruction.	ld.	ld.	ld.
mul	See add instruction.	ld.	ld.	ld.
cmp	Compare the numbers in a and b. If a > b, set the greater than flag. Ditto for equals and less operators, as well.	address a	address b	n/a
rst	Clear the equals, greater, and less than flags.	n/a	n/a	n/a
eld	Write the state of the equals flag to address a. If it's set, than 1 is written; 0 otherwise.	address a	n/a	n/a
gld	Same as eld, but for the greater than flag.	ld.	n/a	n/a
lld	Same as eld, but for the less than flag.	ld.	n/a	n/a
be	Branch to address a if the equal flag is set.	address a	n/a	n/a
bne	Same as be, but the !equal flag.	ld.	n/a	n/a
bg	Same as be, but the greater than flag.	ld.	n/a	n/a
bl	Same as be, but the less than flag.	ld.	n/a	n/a
sto	STOre the immediate value v into address a.	v	address a	n/a
mov	MOVe the value in the address a into address b.	address a	address b	n/a

There are some other instructions, like psto and similar variants. They're experimental.

Instruction design in general

Things we're optimizing for:

• Pack as many things into one instruction as possible. Execution of stuff in instructions is cheap, but each instruction execution is expensive.
• No stacks. Stacks require too much computation on the ISA side itself that isn't provided by the Desmos 'standard library' of instructions.

In general: embed the intelligence into the machine code, not the CPU/ISA!

Things to do

• Write a test suite for the various instruction of the ISA executing in Desmos
• Write an assembler to compile a custom Assembly language to native Desmos list format.
• Simplify all this into a command line tool.
• Simplify the synchronization stack.
• Write documentation for all of this.

Running tests

• Enter the nix-shell, then start a web browser.
• Navigate to https://desmos.com/calculator, and open the dev console
• Run python3 -m cli sync -c to copy the userscript to your clipboard
• Run the userscript in the console
• Run python3 -m unittest ./cli/tests/isa.py, or other test groups if needed
• Keep the Desmos tab focused, as it may impede the ISA testing process

License

This project is licensed under the AGPLv3. See the LICENSE file for more information. Copyright rndusr, randomuser, stupidcomputer 2024.