z80-dis-tiny

Searching for the world's smallest Z-80 disassembler.

Started with the results of the trs8bit newsletter's 2023 competition, this repository tracks the progress of various attempts at the smallest Z-80 disassembler.

The current best is: peter-1 at 871 bytes.

To make the variants comperable and have at least a modicum of practicality they all have the same interface and restrictions on operation. They must:

• Have a subroutine called z80dis
• Disassemble the instruction pointed to by HL register.
• HL points to the next instruction upon return.
• Put the nul terminated disassembly into a buffer pointed to by DE register.
• Support all documented Z-80 instructions.
• Behave reasonably on undocumented instructions (i.e., don't crash, don't output more than 16 bytes to the buffer or put non-ASCII into the buffer).
• Put a single space between the mnemonic and arguments.
• Not output a space after the mnemonic if there are no arguments.
• Output in upper case ASCII.
• Output all numbers in hexadecimal with a $ prefix.
• Use zero-padded, 2 digit hex numbers for 8 bit values.
• Use zero-padded, 4 digit hex numbers for 16 bit values and addresses.
• Show relative branch destinations as addresses.
• Output IX and IY offsets as signed numbers from (IX-$80) to (IX+$7F).
• Use the standard Zilog mnemonics and format for instructions.
• Use V and NV for the P/V flag tests (e.g., opcode $E8 is "RET V").
• Emit RST instructions as "RST $00" through "RST $38".

The size is the sum of both the code and data (initialized or not) and the stack space usage. The subroutine can occupy at most two contiguous regions of memory.