; Formal Model of the JVM - Spring 2007
; J Strother Moore
; Practice Final Exam

; There are five problems.  Each is worth 20 points.  Be sure to
; put your name on your paper!  You have 3 hours to do the five
; problems.  You may use your notes and books.  Laptops are not
; permitted.

; Partial credit will be given.

; During the actual final you will not be allowed to use ACL2.
; But to play with this practice final, you might:

(include-book "m5")

(in-package "M5")

; -----------------------------------------------------------------

; Problem 1.  On the actual JVM, each class description has a
; ``constant pool'' component, which associates 16-bit indices to
; various data structures.  Programs are coded as a strings of
; bytes.  Consider the M5's GETFIELD instruction, which we write
; as (GETFIELD (class field)).  On the JVM, this is coded in three
; successive 8-bit bytes, the first of which is the hex byte B4
; (180, decimal), which stands for GETFIELD.  The next two bytes,
; say x and then y, are combined to form a 16-bit index (with x
; being the high order part and y the low order part) into the
; constant pool.  The data structure at that index contains the
; class and field (strings) we write in the M5 instruction.

; Why does the JVM use the constant pool concept?  Why not put
; the data in the program, as we do in M1?

; -----------------------------------------------------------------

; Problem 2.  An M5 ``method description'' is a keytuple with the
; components :name, :formals, :sync, :code, and :xtbl.  Thus,
; given a method description m, (get :code m) is the list of
; bytecode instructions and (get :xtbl m) is the exception table.

; The exception table is expected to satisfy the specification:

;  An exception table is a list of 4-tuples, each of the form
;  (pc1 pc2 pc3 class), where the pci are legal pcs in the method,
;  pc1 <= pc2, and class is the name of some class in the class
;  table.

; Write an ACL2 function, chk-xt (``check exception table''),
; that takes a method description, m, and a class-table, ct, and
; returns t or nil to indicate whether the method-exception-table
; of m satisfies the above specification.

; -----------------------------------------------------------------

; Problem 3.  Extend M5 to include the new instruction described
; below.  It is sufficient to define execute-XRETURNN.

; Format:  (XRETURNN n)

; Operand Stack:  ... val  => ..., val

; Description: Return val from the nth frame from the current
; one.  If n is 0, this instruction is the same as XRETURN.  If n
; is 1, we return val from the frame that called the current
; frame, etc.  If the call-stack is insufficiently deep, halt the
; machine.

; Note: To play with M5, you might execute (redef) so that you
; can redefine do-inst, but that is not necessary in answering
; this problem.

; -----------------------------------------------------------------

; Problem 4.  Extend M5 to include the new instruction described
; below.  It is sufficient to define execute-INC.
; Format:  (INC n)

; Operand Stack:  ... => ...

; Description: Increment the value of local variable n by 1.

; -----------------------------------------------------------------

; Problem 5.  Extend M5 to include the new instruction described
; below.  It is sufficient to define execute-STORENEW.

; Format:  (STORENEW n class)

; Operand Stack:  ... => ...

; Description: Create a new object of class class and store the
; reference to it into local n.

; -----------------------------------------------------------------