Imager::regmachUser Contributed Perl DocumentaImager::regmach(3p)


NAME
       Imager::regmach - documents the register virtual machine used by
       Imager::transform2().

SYNOPSIS
       The register machine is a complete rewrite of the stack machine
       orginally 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
       colour 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.

       colour registers
           An array of colour 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 colour
       registers with a single output numeric or colour 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 colour) 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.




perl v5.12.2                2006-08-07                          1





Imager::regmachUser Contributed Perl DocumentaImager::regmach(3p)


       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 v5.12.2                2006-08-07                          2