Subleq

Little experiments with the single instruction "SUBtract and branch if Less-than or EQual to zero" language based on this overview.

Source

No assembler yet, so source is whitespace-delimited three-byte groups in files such as helloworld.slq.

Per the above spec example architecture:

• Each instruction is three bytes/operands/addresses: A B C

• A B operand value of -1 outputs the ASCII character at address A

• The value in memory address B is subtracted from that in address A and placed at address B

• If the value at address B is <=0 , jump to address C, else proceed to next instruction

• Coding a jump to a negative address will halt the machine

Compiler

The "compiler" reads filename.slq and creates a binary representation filename.bin (big-endian, two's complement).

Running

The "virtual machine" (such as it is; currently less than 50 LOC) reads filename.bin and executes starting the program counter at memory address 0.

Example

From hi.slq:

 9  -1  3 ; output 'H' (ASCII 72)
10  -1  6 ; output 'i' (ASCII 105)
 0   0 -1 ; halt
72 105  0

hi.bin:

09 ff 03 0a ff 06 00 00 ff 48 69 00

Output:

$ ./subleq.py hi.bin 
Hi
<halt>