Nadleq

Nadleq is an OISC where the one instruction is "Negate and ADd and branch if Less-than or EQual to zero", conventionally abbreviated to nadleq.

Of course, this is derived from the famous Subleq.

Overview

Subleq is a simple one instruction language. Each Subleq instruction has 3 memory address operands. Since Subleq has only one instruction, the opcode itself is conventionally omitted, so each instruction is three addresses long.

Given three operands,

A B C

The execution of an instruction of this form subtracts the value in memory address B from the value in memory address A (the only difference from Subleq!), storing the result into memory address B. If the result stored into memory address B is less than or equal to zero, the execution jumps to the memory address C; otherwise it continues to the next instruction.

For example, in

3 4 6
7 7 7
3 4 0

the first instruction, at address zero, subtracts 7 (address 3) from 7 (address 4). The result in address 4 is 0, so jump to 6. Starting at address 6 is the instruction 3 4 0 which again subtracts now 0 from 7 and halts because the result 7 is larger than zero. Here is a trace of execution (leftmost column is program counter; A and B are shown after subtraction)

0: 3 4 6 A=7 B=0
6: 3 4 0 A=7 B=7
9: Halts

Assembly Syntax

Unlike Subleq, a standard for the assembly syntax exists.

We'll allow program points to be labelled, and for labels to be used in place of addresses, like so:

X Y 6
X:7 Y:7 7
X Y 0

On the first line X refers to a memory cell defined somewhere else. On the second line the address of X is actually defined, by X:7, which means that this address that initially holds 7 has name X.

$ io 256
H=72 io ->
i=105 io ->
halt

On the first line, we created an alias of 256 called io. On the second line, we created a new cell with value 72, prints it. -> refers to the next command. halt compiles to 0 0 -1

NoraTtempt

Nadleq will be used in a cellular-automaton computer called NoraTtempt, which I am currently building.

It's 16-bit, and can theoretically contain 65536 words, but I designed to let it have only 0.5kb RAM which is actually enough for small programs.

The 256th pin is interactive, where you can enter a number in the numpad and see the output with a decimal display.

Implementation

Not yet.