desmos-computer/README.md

desmos-computer

What is this?

• a client-server architecture for synchronizing a file containing Desmos expressions to a graph,
• a test suite for evaluating the 'correctness' of Desmos expressions,
• an instruction set architecture for Turing machines whose cells contain IEEE 754 compliant integers in each cell,
• an assembler for that instruction set architecture,
• and other utilities.

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 evaluating arbitrary Desmos expressions and getting their expected outputs.
• 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.

License

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