README

== About GoLightly ==

GoLightly is a lightweight virtual machine library implemented in Go, designed for flexibility and
reuse. Traditionally popular VMs have adopted a stack-based design as this is perceived to be easier
to implement than the register-based design that real-world hardware generally uses. There are
arguments both ways on which of the two approaches is 'better' and it's not our intention to mandate
either: a good VM toolkit should leave that decision to those who know which suits their purpose best.

However just because GoLightly adopts a careful neutrality on this issue doesn't mean that it has
nothing fresh to offer.

Firstly GoLightly provides support for vector instructions allowing each virtual processor to handle
large data sets more efficiently than in traditional VM designs. Not only is this a boon for fast
maths, it also allows complex data structures to be transferred between virtual processors with only
a couple of instructions.

And speaking of multiple virtual processors, once a processor has been initialised it can be cloned
with a single instruction and both processors are hooked together with a communications channel.

Each processor has its own dynamic instruction definition and dispatch mechanism providing a flexible
model during development. However function-based dynamic dispatch is more expensive than the
switch-based dispatch used in traditional VM designs so the latter is also supported via type
embedding of the ProcessorCore and method hiding of InlinedInstructions().

One interesting consequence of making each virtual processor configurable in this manner is that it
allows complex problems to be modelled in terms of several different processors running relatively
simple programs and arranged in a pipeline.

Likewise the ability to clone virtual processors can be used as a building block for transactional
and speculative execution.


== Tests and Benchmarks ==

Golightly includes a large collection of tests and benchmarks. A simple set of micro-benchmarks
is available to judge the relative cost of various standard Go instructions and idioms which can
be invoked from the command-line:

	cd go
	gotest -benchmarks="Benchmark"


Likewise the test suite for the VM primitives can be executed with:

	cd vm
	gotest

and the optional benchmarks invoked with:

	gotest -benchmarks="Benchmark"

These include extensive micro-benchmarks focusing on individual primitive operation performance which
will hopefully act as a useful guide to relative performance for those writing compilers or assemblers
targeting GoLightly virtual machines.