Redcode

From Esolang
Jump to: navigation, search

Redcode is an esoteric programming language designed by A. K. Dewdney and David Jones in autumn 1983 and first described in the May 1984 issue of Scientific American. The purpose of Redcode is to provide an environment for Core War, in which programs attempt to crash their opponents. Redcode is (almost) Turing Complete in the same sense as C, where any given program must run within finite memory space but may be agnostic to the exact size.

Instructions

Opcode Description
DAT When executed, the current process is terminated
MOV Copies the contents of the A-field to the B-field
ADD Adds the contents of the A-field to the contents of the B-field
SUB Subtracts the contents of the A-field from the contents of the B-field
MUL Multiplies the contents of the A-field by the contents of the B-field. Redcode-94 only.
DIV Divides the contents of the A-field by the contents of the B-field. Division by zero terminates the executing process. Redcode-94 only.
MOD Divides the contents of the A-field by the contents of the B-field and sets the B-field to the remainder. Modulus by zero terminates the executing process. Redcode-94 only.
JMP Transfers control to the location specified in the A-field
JMZ Transfers control to the A-field location if the B-field is 0
JMN Transfers control to the A-field location if the B-field is not 0
DJN Decrements the B-field. Transfers control to the A-field location if the B-field is not 0
SEQ Skips the next instruction if the A-field and B-field are equal. CMP is a synonym
SNE Skips the next instruction if the A-field and B-field are not equal. Redcode-94 only.
SLT Skips the next instruction if the A-field is less than the B-field
SPL Start a new process at the location specified by the A-field
NOP Do nothing
STP Copies the A-field to the private memory specified by the B-field. Redcode-94 only, and only on hills where P-space is allowed.
LDP Copies the private memory specified by the A-field to the B-field. Redcode-94 only, and only on hills where P-space is allowed.
STS Write the character in the A-field to STDOUT. Non-standard.
LDS Read a character from STDIN and store in the A-field. Non-standard.

Example

Hello, World

This program prints out the words Hello, World!:

; Redcode Hello World, John Metcalf

write   sts.a  hello,     0
        sts.b  }write,    0
        djn    write,     #7
 
hello   dat    72,        101 ; He
        dat    108,       108 ; ll
        dat    111,       44  ; o,
        dat    32,        87  ;  W
        dat    111,       114 ; or
        dat    108,       100 ; ld
        dat    33,        10  ; !\n

Imp

This program copies itself forward forever, turning other processes into copies of itself. Somewhat hard to kill, but always overwrites enemies with executable instructions. Note that this program relies on the fact that all Redcode addressing is relative--in fact, no position in memory is privledged in any way as the "first", since Redcode memory is circular.

; "Imp", A. K. Dewdney
        mov    0,         1
; Alternate versions using redcode-94 instruction modifier semantics:
        mov.i  #8,        1 ; A-field can store arbitrary data.
        mov.i  #1,       *0 ; Copies itself via A-field indirection.

Dwarf

This was the first offensive program. It scores 25% wins and 75% ties against Imp, and 37.5% wins, 37.5% losses, and 25% ties against itself. Additionally, in cores of size divisible by four (which are very common), it will never overwrite its execution footprint with a terminal DAT. By modern standards, though, it is very weak.

; "Dwarf", A. K. Dewdney
        mov   4,          @4 ; Move the bomb to the location pointed to by the bomb. (B-indirect.)
        add   #4,         3  ; Immediate add adds the immediate A-operand to the B-field of the cell pointed to by the B-operand.
        jmp   -2             ; Jump back two steps (to the MOV)
        dat   #4             ; The bomb. After enough cycles, dwarf will overwrite the bomb with itself, harmlessly. It then restarts the bombing run.

External resources