[SOLVED] C data structure The project

The project

Cthe interpreter
Two partner teams
Send me email with your partner name. Copy your partner on it
We will implement an interpreter or virtual machine

It will execute programs that are a string of bytes Well have test examples available on Piazza

What the input looks like
offset in
file
0
1 2
8 bits
8 bits
8 bits
.. .
8 bits
n1
Contents of the file are a stream
of bytes that represent instructions and data

The input should be read in as a file of bytes

Main data structures in the interpreterthe memory
Memory
69 pushs instruction

In the simplest form, this is the array of bytes holding the program
The input file is read into memory
0
4 69 0
7 100
short pushed
pushs instruction short pushed
add instruction

69
0
4
69
0
7
100
. ..

Main data structures in the interpreterthe program counter pc
pushs instruction short pushed
pushs instruction short pushed
add instruction
The program counter
69 0
4 69 0
7 100

This is an index into the memory that gives the next memory location to be accessed
This is often the next instruction pc3

69
0
4
69
0
7
100
. ..

Main data structures in the interpreterthe runtime stack and runtime stack pointer rsp
rsp
The runtime stack

Holds operands to be acted on
holds local variables
holds arguments to functions

69
0
4
69
0
7
100
. ..

The program begins and the pushs instruction begins execution
rsp
Main data structures in the interpreterthe runtime stack and runtime stack pointer rsp
69
0
4
69
0
7
100
. ..

Main data structures in the interpreterthe runtime stack and runtime stack pointer rsp
After the first pushs executes, the next pushs is executed
rsp
short object 4
69
0
4
69
0
7
100
. ..

Main data structures in the interpreterthe runtime stack and runtime stack pointer rsp
This shows the stack after the second pushs executes
The add will be executed next rsp
short object 4

short object 7
69
0
4
69
0
7
100
. ..

Main data structures in the interpreterthe runtime stack and runtime stack pointer rsp
short object 11

After the add executes
rsp

The add knows what it is adding because of the types of the objects on the stack
We can use operator overloading to do the operation
69
0
4
69
0
7
100
. ..

Function call instructions
When a function is called not necessarily in this order
the stack pointer for the calling function is saved so that it can be restored when the function returns to its caller
arguments are pushed onto the stack
the program counter to the instruction after the function call code is put on the stack so the called function can jump back to it
the code at the start of the function is jumped to

We have a stack to save frame
frame pointer stack
stack pointers
main calls foo calls func calls method
main fp
foo fp
func fp

frame stack pointer

Some instructions
add: 100, or 01100100
rstacksp1rstacksp1rstacksp sp;
printi, 150, or 10010110. Print the integer at the top of the stack System.out.printlnrstacksp;

Some instructions
jmp: 36, or 00100100
meaning: jump to the location at the top of the runtime stack. pcrstacksp
spsp1;
jmpc: 40, or 00101000
meaning: jump to the location at the top of the runtime stack is the next
if rstacksp1 pcrstacksp
spsp2

Some instructions
call: 44, or 00101100
meaning: save the stack pointer for the current frame in the fpstack frame pointer stack. Jump to the location of the function being called, whose address is on the top of the runtime stack. fpstackfpspsprstacksp;subtract off argument stack
entries
sp;
pcrstackspset the PC to the address of the label to be
jumped to

Some alternatives to implementing this
Simply have the memory be an array of bytes that are accessed directly worst
Have memory be part of an object that returns objects that correspond to the type of value stored in a memory location, i.e., a pushs byte code, a short value good, good performance
Have memory be an array of pointers to objects representing the value in a memory location good, good performance

Some alternatives to implementing this
Have memory be part of an object that returns objects that correspond to the type of value stored in a memory location, i.e., a pushs byte code, a short value good, good performance
different kinds of byte codes should inherit from a base abstract byte code class, which in turn inherits from an abstract memory object class
pc

69
0
4
Bytecode bcgetMemorypc; Short sgetMemorypc; pc;
execute a push with s

Have memory be part of an object that returns objects that correspond to the type of value stored in a memory location, i.e., a pushs byte code, a short value good, good performance
different kinds of byte codes should inherit from a base abstract byte code class, which in turn inherits from an abstract memory object class
pc

Another way to implementing this
69
0
4
Bytecode bcgetMemorypc; bcexecute ;fetches the short
from memory andpush it onto the
stack

Some alternatives to implementing this
Have memory be an array of pointers to objects representing the value in a memory location good, good performance

pc
pushs object short object 4
NULL

Some alternatives to implementing this
Have memory be an array of pointers to objects representing the value in a memory location good, good performance

pc
pushs object short object 4
bool conttrue; while cont
contmemorypcexecute ;
NULL