4 tridigits, 169 tridigytes

4 tridigits, 169 tridigytes is yet another programming language designed by PSTF. It is inspired by 2 undigits, 121 undigytes by Mutasimos which is inspired by 7 heptits, 49 heptytes by PSTF which is inspired by 3 pentits, 25 pentytes by Mutasimos.

Terminology

• Tridigit: A single base-13 digit.
• Tridigyte (TY): A group of 2 tridigits.
• Word: A group of 2 TYs.
• Memory consists of 169 TY, addressed linearly from 00 to CC (decimal 0 … 168).

Registers

There are 4 general-purpose word-wide registers, notated with A, SP, PC and FS.

At the beginning, the SP points to the highest memory location, that is CC₁₃.

FS consists of "ZF" and "NF" for zero and negative.

ALU supports four arithmetic operations(division are seperated into integer division and modulo), along with increment and decrement.

Arithmetic is modulo 13⁴; signed interpretation:

A is negative if its most significant trit ≥ 7 (i.e. A ≥ 7CCC).

Instruction size: 2 TY (4 trits), aligned on even‑numbered TY addresses. PC advances by 2 after each instruction fetch.

Instruction Set

All instructions use the 2‑tridigit opcode + 2‑tridigit operand format:

[ opcode (2 trits) ] [ operand (2 trits) ]

The operand is a TY address (00 … CC) for memory ops, or ignored for unary I/O.

================COMMAND SHEET================
00. NOP        : No operation.
01. LDA    addr: Load a word from addr to addr+1 to A.
02. STA    addr: Store the highest two tridigits of A to addr while lowest two ones to addr+1.
03. ADD    addr: A ← A + word(addr).
04. SUB    addr: A ← A - word(addr).
05. JMP    addr: Jump unconditionally.
06. JEQ    addr: Jump if ZF = 1.
07. JLT    addr: Jump if NF = 1.
08. INC        : A++.
09. DEC        : A--.
0a. OUT        : Output A as tridecimal number.
0b. IN         : Input a tridecimal number to A.
0c. HLT        : Halt.
10. PUTC       : Output A as a character. Codepage is same as ASCII while the value greater than 127 are ignored or printed as question mark.
11. GETC       : Input a character to A.
12. MUL    addr: A ← A * word(addr).
13. DIV    addr: A ← A / word(addr), results in integer.
14. MOD    addr: A ← A mod word(addr).
15. JNE    addr: Jump if ZF = 0.
16. JGE    addr: Jump if NF = 0.
17. JLE    addr: Jump if either ZF or NF is 1.
18. JGT    addr: Jump if both ZF and NF is 0.
19     ~     cc: Reserved.

Addressing and Self-Modification

Direct addressing is the only built‑in mode, but self‑modifying code provides full indirect addressing, making the ISA universal.

Indirect load via self‑modification:

    LDA TARGET_ADDR   ; A holds the desired address (0..CC)
    STA PATCH+1       ; write low TY of A into operand field of instruction below
PATCH:
    LDA 00            ; this instruction is patched to LDA <target>
    ...               ; now A contains word from target address

Because we can compute addresses, store them, and patch operands, we can implement arbitrary indirect reads/writes, conditionals, and loops. Combined with arithmetic and branching, this yields a Turing‑complete model (provided memory is conceptually unbounded).

I/O Details

Numeric I/O (IN/OUT):

• Input: reads a token consisting of base‑13 digits (0‑9A‑C) until whitespace; parses it into a 4‑tridigit word (leading zeroes allowed).
• Output: prints A as a base‑13 number without leading zeroes (zero prints as 0).

Character I/O (GETC/PUTC):

• Input: reads a single character from stdin, stores its ASCII value (0‑127) in A.
• Output: converts (A mod 169) to an ASCII character and prints it. Values > 127 are printed as ? (or ignored – implementation defined).

Assembler Syntax & Example

• Comments start with ;.
• Labels: label: (placed on a separate line before an instruction).
• Directives: .ORG <addr> sets the starting TY address for subsequent code/data.
• Constants: base‑13 literals (e.g. A3, 1C0, 00) or ASCII using single quotes (e.g. 'X' gives ASCII code).

Examples

Cat Program

.ORG 00
LOOP:
    INCHR        ; read a char into A
    JZ DONE      ; if EOF (0) jump to halt
    OUTC         ; echo the character
    JMP LOOP
DONE:
    HLT

See Also

• 2 undigits, 121 undigytes