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Assembler and runner for the Intcode computer from Advent of Code 2019.

The following program outputs "Hello World!".

    ARB #message  ; move the relative base to the beginning of our messageloop:OUT rb        ; output the current character in the message    ARB #1        ; move the relative base to the next characterJNZ rb, #loop ; if the next character is non-zero then go back to `loop`HLTmessage:DB"Hello World!\n"

The compiler can assemble the following instruction set specification into anIntcode program.

Intcode assembly must be written in a UTF-8 encoded file with Unix line endings.Comments start with a semicolon;.

There are two types of operands.

• Label

  A label refers to an address in a program. For example:end in the following program refers the address of theHLT instruction.

  JZ #0, #endend:HLT

• Number

  A binary, octal, decimal, or hexadecimal number. This can be used forspecifying manual addresses, address offsets, or exact values. For example:the following reads in a value, minuses 3 from it, and outputs the result.

  IN  xADD x, #-0b11, x+1OUT x+0x1HLT

There are three ways to specify the operands for different instructions.

• Positional

  Specifies a value by specifying theaddress it should be read from. Forexample:

  • 19 specifies the value at address 19.
  • x+3 specifies the value at the labelx with an offset of 3.

• Immediate

  Specifies a value by specifying the exact value. For example:

  • #19 specifies the exact value 19.
  • #x+3 specifies the exact label addressx with an offset of 3.

• Relative

  Specifies a value by specifying theaddress it should be read from as anoffset of therelative base. For example:

  • rb+3 specifies the value at the relative base address with an offset of 3.

The following operations are supported, roughly described in the order they areintroduced in Advent of Code.

• ADD

  Adds the first two operands and stores the result in the third. For example:increment the value atx:

  ADD x, #1, x

• MUL

  Multiplies the first two operands and stores the result in the third. Forexample: multiply the value atx by 2:

  MUL x, #2, x

• IN

  Reads a single number and stores it in the first operand. For example: storeinput atx:

  IN x

• OUT

  Outputs a single number and stores it in the first operand. For example:output the value atx:

  OUT x

• JNZ

  Checks if the first operand is non-zero and then jumps to the value of thesecond operand. For example: set the instruction pointer tolabel if thevalue atx is non-zero:

  JNZ x, #label

• JZ

  Checks if the first operand is zero and then jumps to the value of the secondoperand. For example: set the instruction pointer tolabel if the value atx is zero:

  JZ x, #label

• LT

  Checks if the first operand is less than the second. If true, stores 1 in thethird operand else stores 0. For example: check if the value atx is lessthan 7 and store the result inresult:

  LT x, #7, result

• EQ

  Checks if the first operand is equal to the second. If true, stores 1 in thethird operand else stores 0. For example: check if the value atx is equalto 7 and store the result inresult:

  EQ x, #7, result

• ARB

  Adjusts the relative base to the value of the first operand. For example: setsthe relative base to themessage address:

  ARB #message

• HLT

  Halts the program. For example:

  HLT

• DB

  Places raw data into the program. This must be a sequence of numbers orstrings. Strings will be encoded as UTF-8. A label on aDB instruction willrefer to the start of the data. For example the following specifies the string"Hello World!" with a newline.

  message:DB"Hello World!",10

• _

  Refers to an undefined address. This should be used to indicate that theaddress will be set at runtime.

• ip

  Refers to the address of the next instruction. This can be used to dereferencea pointer.

Consider the following example whereptr refers to some address and we want toread a value into that address._ is used because the value ofptr will befilled as the parameter for theIN instruction by theADD instruction.

ADD ptr, #0,ip+1IN  _HLT

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