Manual Reference Pages - IMAGER::REGMACH (3)
Imager::regmach - documents the register virtual machine used by
The register machine is a complete rewrite of the stack machine
originally used by Imager::transform(), written for use by
(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:
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 doesnt check register numbers
An array of instructions
An array of numeric registers. Some registers are initialized as
An array of color registers. Currently these registers arent
An array of Imager i_img pointers. The getpn operators read pixels
from these images.
The final instruction must be a ret instruction, which returns the
Adding new instructions
To add a new instruction:
The Makefile should rebuild the Regops.pm file, and your new
instruction will be added as a function.
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.
Add a case to regmach.c that executes the instruction.
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.
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 well have a very significant
If you feed bad machine code to the register machine, you have a
good chance of a SIGSEGV.
Tony Cook <firstname.lastname@example.org>, Arnar M. Hrafnkelsson
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