Yet Another Virtual Machine - Stack Instructions

OPCODE: 00000

• If the flag has operand is set:
  • read X byte(s) following the instruction
  • increment the value of the IP register by X
  • copy the bytes at the address SB + SP where SB is the address of the stack base, and SP the stack pointer register
  • increment the value of the SP register by X
• Else:
  • read X byte(s) at the address SB + SP - X
  • copy the bytes at the address SB + SP
  • increment the value of the SP register by X

Instruction	Value for X
PUSH8	1
PUSH16	2
PUSH32	4
PUSH64	8

PUSH16 0xDEAD

⇩

PUSH16 (1 00000 01)

0xDE

0xAD

⇩

STACK HEAD (SP = 2)
0xAD
0xDE
STACK BASE

OPCODE: 00001

• decrement the value of SP by X
• if the value is less than 0, reset it to 0

Instruction	Value for X
POP8	1
POP16	2
POP32	4
POP64	8

PUSH16 0xDEAD
POP8

⇩

PUSH16 (1 00000 01)	0xDE	0xAD
POP8 (0 00001 00)

⇩

STACK HEAD (SP = 1)
0xDE
STACK BASE

OPCODE: 00010

• swap the two last X bytes of the stack

Instruction	Value for X
SWAP8	1
SWAP16	2
SWAP32	4
SWAP64	8

PUSH16 0xDEAD
PUSH16 0xBEEF
SWAP16

⇩

PUSH16 (1 00000 01)	0xDE	0xAD
PUSH16 (1 00000 01)	0xBE	0xEF
SWAP16 (0 00010 01)

⇩

STACK HEAD (SP = 4)
0xAD
0xDE
0xEF
0xBE
STACK BASE

OPCODE: 00011

• pop the two last X bytes from the stack
• push the last X bytes on the stack
• push the second last X on the stack
• push the last X bytes on the stack
• increment the value of SP register by X

Instruction	Value for X
TUCK8	1
TUCK16	2
TUCK32	4
TUCK64	8

PUSH16 0xDEAD
TUCK8

⇩

PUSH16 (1 00000 01)	0xDE	0xAD
TUCK8 (0 00011 00)

⇩

STACK HEAD (SP = 3)
0xAD
0xDE
0xAD
STACK BASE