Assembly vs BASIC

10 Print is a "native" BASIC program, which is just to say that it was originally written in BASIC for the C64, and not first rendered in assembly and later reimplemented. For that reason, no canonical assembly program exists. As with literary translation or artistic adaptation, there are multiple ways to recast a computer program from one language into another, even on a relatively simple system like the C64, and even with a relatively simple program like 10 Print. The following rendition was authored by Ian Bogost, Stephane Hockenhull, and Nick Montfort, in the context of the demo scene event @party in July 2010.

10 Print is a "native" BASIC program, which is just to say that it was originally written in BASIC for the C64, and not first rendered in assembly and later reimplemented. For that reason, no canonical assembly program exists. As with literary translation or artistic adaptation, there are multiple ways to recast a computer program from one language into another, even on a relatively simple system like the C64, and even with a relatively simple program like 10 Print. The following rendition was authored by Ian Bogost, Stephane Hockenhull, and Nick Montfort, in the context of the demo scene event @party in July 2010.

*= $1000 ; starting memory location

*= $1000 ; starting memory location

jsr $ffd2 ; output character via kernal routine

jsr $ffd2 ; output character via kernal routine

bne loop ; repeat

bne loop ; repeat

[Note: a complete, line-by-line explication of this program is needed, but I've omitted it for the time being, since such an act is really just an exercise and won't require much thinking to do, just time.]

[Note: a complete, line-by-line explication of this program is needed, but I've omitted it for the time being, since such an act is really just an exercise and won't require much thinking to do, just time.]

But as with the SID random number solution, the C64's underlying hardware ROM provides a much simpler solution. The C64 has a low-level operating system core, most of which it inherited from the earlier Commodore PET. This core is referred to as the KERNAL, and it occupies the last 8KB of the machine's address space ($E000-$FFFF). The KERNAL handles keyboard input and screen output, among other functions, including a routine that will send the PETSCII character value currently in the 6502 processor's accumulator to the current output device (the screen by default). That routine lives at memory address $ffd2, and it can be executed by jumping to subroutine at that address. This is just what the 10 Print assembly rendition above does, after loading a random value and manipulating it to insure that it will be one of the two slash characters that comprise the maze:

But as with the SID random number solution, the C64's underlying hardware ROM provides a much simpler solution. The C64 has a low-level operating system core, most of which it inherited from the earlier Commodore PET. This core is referred to as the KERNAL, and it occupies the last 8KB of the machine's address space ($E000-$FFFF). The KERNAL handles keyboard input and screen output, among other functions, including a routine that will send the PETSCII character value currently in the 6502 processor's accumulator to the current output device (the screen by default). That routine lives at memory address $ffd2, and it can be executed by jumping to subroutine at that address. This is just what the 10 Print assembly rendition above does, after loading a random value and manipulating it to insure that it will be one of the two slash characters that comprise the maze:

jsr $ffd2 ; output character via kernal routine

jsr $ffd2 ; output character via kernal routine

The output of the assembly program is essentially identical to 10 Print (it runs a bit faster, because the microprocessor is running machine instructions directly, rather than interpreting them first as BASIC commands and functions. But the program that generates that output is really no more or less lengthy or complex than is the BASIC program. When measured in bytes, the assembly program is even shorter than its BASIC cousin (22 bytes for the assembly program, compared to 36 bytes, or characters, for the BASIC program). While the assembly program is clearly more esoteric and less human readable than the BASIC one, its implementation teaches us that the abstraction that makes the emergent elegance of 10 Print's output possible in such a small set of instructions is not a feature of the BASIC interpreter, but of the underlying hardware itself.

The output of the assembly program is essentially identical to 10 Print (it runs a bit faster, because the microprocessor is running machine instructions directly, rather than interpreting them first as BASIC commands and functions. But the program that generates that output is really no more or less lengthy or complex than is the BASIC program. When measured in bytes, the assembly program is even shorter than its BASIC cousin (22 bytes for the assembly program, compared to 36 bytes, or characters, for the BASIC program). While the assembly program is clearly more esoteric and less human readable than the BASIC one, its implementation teaches us that the abstraction that makes the emergent elegance of 10 Print's output possible in such a small set of instructions is not a feature of the BASIC interpreter, but of the underlying hardware itself.