My Entry to Advent of Code 2019

Learning Rust by doing https://adventofcode.com/2019.

Advent

Build and run

The project does not actually uses any new features in Rust nightly, but it still requires nightly to build. I have some procedure macros in advent/meta.rs. Somehow it seems to conflict with my makeIntEnum macro. Either of them builds fine in Rust stable alone, but they do not build at the same time…​ The problem is gone in nightly.

Run cargo build to build, and run cargo run DAY PART to run. The following example run day 5, part 2.

cargo run 5 2

In all cases, the input is taken from stdin, and output is printed to stdout, together with time duration of the run.

Code arrangement

Intcode

The Intcode puzzles are so fun, I decided to write a dedicated emulator and an assembler for it. To run the emulator, run

cargo run --bin emulator -- FILE

where FILE is the file containing your Intcode source code. It takes input from stdin (if there’s no input, you still need to press ctrl+d), and output to stdout.

To run the assembler, run

cargo run --bin assembler

The assembler read what I call “inssembly” code from stdin, and assemble it to Intcode, which is output to stdout. Here’s an example inssembly that does integer division:

; Integer division

input arg1
input arg2

addition:
add 1, result, result
mult result, arg2, test

eq test, arg1, equal_result
jmpt equal_result, :output

less arg1, test, less_result
jmpt less_result, :minus1       ; We overshot, need to minus 1.

jmpt 1, :addition

output:
output result

halt

minus1:
add -1, result, result
jmpt 1, :output

Besides the instruction provided by Intcode, inssembly also support functions. Here’s an example that demonstrate function calls

    add 50, 50, add1_arg1
    add 1, 2, add1_arg2
    call :the_add
    output add1_result
    halt
the_add:
    add add1_arg1, add1_arg2, add2_arg1
    call :add2
    add add2_result, 0, add1_result
    rtn

add2:
    add add2_arg1, 2, add2_result
    rtn

Basically it defines a function the_add, which adds its 2 arguments and apply another function add2 on it. The function add2 just adds 2 to its only argument. Function calls are implemented by pre-allocating a stack after the “text segment”. The size of the stack is currently hard-coded to be 10. The “arguments” and “return values” are all “static”.