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The Addie VM

Addie is an interpreted language for maximum portability. To be fast and efficient, we have chosen a register based virtual machine architecture.

Our fixed size bytecode instruction

Bytecode instructions are fixed in size (64 bits). The cost of having 64 bit instructions is offset by the fact that there are combinatory instructions for common operational sequences such as CALL_IF_TRUE_GOTO and MOVE_MOVE.

Registers

There are 32 general purpose 64 bit registers named r0 to r31. The register r0 is used to store return values. In addition, there are a few fixed purpose registers.

Addresses

Memory addresses occupy 24 bits and points to slots. Each slot is 64 bytes wide.

The operation layout

The OP code uses 8 bits. The structure of the remaining 56 bits depend on the OP code at hand.

63-56	55-48	47-40	39-32	31-24	23-16	15-8	7-0
A	B	C	D	E	F	G	OP
A2		C2		D2		G	OP
A3			D2		F2		OP
A4				E3			OP
A5					F2		OP
A6						G	OP
A7							OP

Depending on the operation, the operands are of mixed numbers and sizes (4, 8, 16, 24, 32, 40, 48 or 56 bit). However, the operands always amount to 56 bits. The 4 bit operands are named Al/Ah, Bl/Bh, etc.

The core instruction set

As Addie is (potentially) interpreted, we will try to use as many high level OPs as possible. To make comprehension simpler, we divide the OP codes into the core set and the extended set. The OP prefix and OP suffix are for mnemonics only, the two are baked together into a single byte.

OP prefix	OP suffix	Description
MOVE	rr ra ar aa	Move data between registers and memory
LOAD		Load a value into a register
CALL	noarg fixarg vararg	Call a subroutine (by polymorphic combination or message and arguments)
GOTO		Jump to an address
RETURN	void,val	Return from a subroutine
IF_TRUE_GOTO	r0 rx	Conditional jump
IF_FALSE_GOTO	r0 rx	Conditional jump
CLOSURIZE		Create a closure

The extended instruction set

To make efficient use of the 64 bit instruction set, common combinations are baked into a single operation. Also, if data types are known, fixed operations can be performed.

OP prefix	OP suffix	Description
MOVE_MOVE	rara arar rarr arrr rrrr	Move data between registers and memory.
LOAD_LOAD	48_8 32_16 24_24	Load two values into two registers
CALL_IF_TRUE_GOTO		Conditional jump
CALL_IF_FALSE_GOTO		Conditional jump

Static function and type instruction set

If data types and functions are statically known, fixed code operations can be performed. However, in Addie, this is not usually the case.

OP prefix	OP suffix	Description
FIXED_CALL	noarg fixarg vararg	Call a fixed subroutine. This can be done is there is a guarantee of a non polymorphic implementation
IF_EQUAL_GOTO		Conditional jump
IF_NOT_EQUAL_GOTO		Conditional jump
IF_SMALLER_GOTO	i f	Conditional jump
IF_ATMOST_GOTO	i f	Conditional jump
IF_ATLEAST_GOTO	i f	Conditional jump
IF_LARGER_GOTO	i f	Conditional jump
INC_IF_SMALLER_GOTO	i f	Conditional jump
INC_IF_ATMOST_GOTO	i f	Conditional jump
DEC_IF_ATLEAST_GOTO	i f	Conditional jump
DEC_IF_LARGER_GOTO	i f	Conditional jump
ADD	i f	Add
SUB	i f	Subtract
MUL	i f	Multiply
INC	i f	Increment
DEC	i f	Decrement