Imager::regmach(3) User Contributed Perl Documentation Imager::regmach(3)NAMEImager::regmach - documents the register virtual machine used by
Imager::transform2().
SYNOPSIS
The register machine is a complete rewrite of the stack machine
originally used by Imager::transform(), written for use by
Imager::transform2().
DESCRIPTION
(This document might be a little incoherent.)
The register machine is a fast implementation of a small instruction
set designed for evaluating an arithmetic expression to produce a color
for an image.
The machine takes as input:
instructions
An array of instructions
numeric registers
An array of numeric registers. Some registers are initialized as
literals.
color registers
An array of color registers. Currently these registers aren't
initialized.
input images
An array of Imager i_img pointers. The "getpn" operators read
pixels from these images.
The instructions supplied each take up to 4 input numeric or color
registers with a single output numeric or color register. The machine
attempts to execute instructions as safely as possible, assuming that
correct instructions have been provided, eg. the machine protects
against divide by zero, but doesn't check register numbers for
validity.
The final instruction must be a "ret" instruction, which returns the
result ;)
Adding new instructions
To add a new instruction:
1. Add a new opcode to the enumeration in regmach.h - make sure to add
comment after the enum name giving the input registers ("rX" for
numeric, "pX" for color) that the instruction takes. These must be
in the order that the instruction expects to take the. Put a
letter (r or p) after -> to indicate the result type.
2. Add a case to regmach.c that executes the instruction.
3. make
The Makefile should rebuild the Regops.pm file, and your new
instruction will be added as a function.
If you want to add a single alternative instruction that might take
different argument types (it must take the same number of parameters),
create another instruction with that name followed by a p. The current
expression parsers explicitly look for such instruction names.
Future directions
Conditional and non-conditional jumps to implement iteration. This
will break the current optimizer in Imager::Expr (and the compilers for
both expression compilers, for that matter.)
Complex arithmetic (Addi suggested this one). This would most likely
be a separate machine. Otherwise we'll have a very significant
performance loss.
WARNINGS
If you feed bad 'machine code' to the register machine, you have a good
chance of a "SIGSEGV".
perl v5.14.3 2012-09-28 Imager::regmach(3)
