Org starts a new section, with a new base and offset.

; Patching macros
; v0.60
; for flat assembler by Grom PE

; How it works:
; - File name and size are specified with "patchfile"
; - On every "patchat", part of file is loaded and added,
;   (or zeroes if file is ended) assembling point moves to
;   specified offset.
; - On "patchend", if there part of file left, it is added.
; - "patchsection x" makes every following "patchat" macro
;   act like "org x" was placed after it.

; Notes:
; - Don't use "org" directive between all patching macros!

;  For good example on how to use patching macros look:
;  http://board.flatassembler.net/topic.php?t=8876

p_savedorg = 0
p_sectionset = 0

macro pushorg value*
{
  p_wasorg = $
  org value
  p_inorg = $
  p_savedorg = 1
}

macro poporg
{
  local orgsize
  orgsize = $ - p_inorg
  org p_wasorg + orgsize
  p_savedorg = 0
}

macro patchsection value*
{
  p_sectionset = 1
  p_sectionorg = value
}

macro patchfile name*
{
  virtual
    @@:
    file name
    p_filesize = $ - @b
  end virtual
  p_start = $
  p_pointer = 0
  p_filename equ name
}

macro patchat address*
{
  if p_savedorg = 1
    poporg
  end if

  p_pointer = p_pointer - p_start + $
  p_toadd = address - $

  if address >= 0
    if p_toadd >= 0
      if p_pointer + p_toadd <= p_filesize
        file p_filename: p_pointer, p_toadd
      else
        p_addpart = 0
        if p_pointer < p_filesize
          p_addpart = p_filesize - p_pointer
          file p_filename: p_pointer, p_addpart
        end if
        rb p_toadd - p_addpart
      end if
    else
      "Error: can't move backwards."
    end if
  else
    "Error: invalid address, must be >= 0."
  end if

  p_start = $
  p_pointer = p_pointer + p_toadd

  if p_sectionset = 1
    pushorg p_sectionorg + address
  end if
}

macro patchend
{
  if p_savedorg
    poporg
  end if

  p_pointer = p_pointer - p_start + $
  p_toadd = p_filesize - $

  if p_toadd >= 0
    if p_pointer + p_toadd <= p_filesize
      file p_filename: p_pointer, p_toadd
    else
      p_addpart = 0
      if p_pointer < p_filesize
        p_addpart = p_filesize - p_pointer
        file p_filename: p_pointer, p_addpart
      end if
      db p_toadd - p_addpart dup 0
    end if
  end if
}