hellerve/vvm: A basic virtual machine - vvm

Performance is pretty okay on basic, small programs. The included factorial function takes 0.1 second on 100000 iterations. As a scale, a Python 3.3 program on the same machine using the code:

def fac(n): if n < 2: return 1 else: return n * fac(n-1) fac(12)

takes about 3.7 seconds on 100000 iterations.

This does not say anything about overall performance though and I am not sure whether this small, funny test has any real value in measuring performance. Also, Python is much more feature-rich, so you cannot compare the two at all.

DISCLAIMER: Parsing takes quite a long time, so try to write your programs as concise as possible.

Instruction set

Up until now, all the operations are executed on integers(hence the I* prefix).

Operations overview:

ENTRY - Specifies an entry point for the routine by its index.
IADD - Adds the two items to each other that are on top of the stack and stores the result on top of the stack.
ISUB - Subtracts the two items from each other that are on top of the stack and stores the result on top of the stack.
IMULT - Multiplies the two items to each other that are on top of the stack and stores the result on top of the stack.
IDIV - Performs a division operation to the two items that are on top of the stack and stores the result on top of the stack.
IMOD - Performs a modulo operation to the two items that are on top of the stack and stores the result on top of the stack.
ILT - Checks whether the item on top of the stack is greater than the item below it and stores a boolean on top of the stack.
IEQ - Checks whether the item on top of the stack is equal to the item below it and stores a boolean on top of the stack.
IGT - Checks whether the item on top of the stack is smaller than the item below it and stores a boolean on top of the stack.
ILEQ - Checks whether the item on top of the stack is smaller than or equal to the item below it and stores a boolean on top of the stack.
IGEQ - Checks whether the item on top of the stack is greater than or equal to the item below it and stores a boolean on top of the stack.
BR - Jumps to the instruction that is provided as an argument.
BRT - Jumps to the instruction that is provided as an argument if the value on top of the stack is TRUE.
BRF - Jumps to the instruction that is provided as an argument if the value on top of the stack is FALSE.
ICONST - Puts the argument provided to the operation on top of the stack.
LOAD - Loads an element from any position on the stack on top of the stack(usually used to get function arguments like this: LOAD -3).
GLOAD - Loads an element from any position on the data segment on top of the stack.
STORE - Stores an element on the stack.
GSTORE - Stores an element in the data segment.
PRINT - Prints the element on top of the stack as character.
IPRINT - Prints the element on top of the stack as integer.
POP - Pops the element on top of the stack.
HALT - Ends the program.
CALL - calls a subroutine with a number of arguments.
RET - Returns from a subroutine with a return value.
FETCH - Fetches a value.
IINC -Increments the value on top of the stack by one(equal to ++).
IDEC -Decrements the value on top of the stack by one(equal to --).