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The DIdactic VAnity REgister MAchine

This is a pet-project interpreter which implements a random access
machine as described by
Cook and Reckhow.

divarema only implements the machine's basic instructions; the paper
linked above also includes a proof regarding a VM built with these
instructions which can execute arbitrary programs stored in main
memory within some time bounds (so an arbitrarily large program can be
executed with a space-bounded instruction and ROM program).

Motivation

This is a pet project to help me learn about models of computation and
about Rust (hence didactic and vanity). It's not intended for any
other application, but if you get something from it that's great :)

The Machine

divarema reads instructions form a file and executes them. The
machine has eight instructions and two kinds of memory. Program memory
stores the program being executed and is immutable. Main memory is
available to the program and consists of a number (by default, 8) of
mutable registers that can hold signed 32-bit integers. Main memory is
indexed by integers, starting from 0.

Two special registers control operation and implement arithmetic:

  • The accumulator ACC is the target and source of arithmetic and copy
    operations
  • The instruction counter IC holds the address (in program-memory)
    of the next instruction to execute, manipulated by control-flow
    operations

Instruction Set

Programs for divarema can include the following instructions:

Operation Description Mnemonic
LOAD j ACC <- j ; IC <- IC+2 load
ADD j ACC <- [ACC] + [Xj] ; IC <- IC+2 add
SUB j ACC <- [ACC] - [Xj] ; IC <- IC+2 subtract
STORE j Xj <- [ACC] ; IC <- IC+2 store
JGZ j if AC > 0 then IC <- j else IC <- IC+2 jump-greather-than-zero
READ j Xj <- next input read
PRINT j output [Xj] print
HALT _ stop execution halt

License

This software is licensed under the GNU General Public License
v3.0. See LICENSE
or license's website
for details.