Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!ADAM.BYU.EDU!rohran
From: rohran@ADAM.BYU.EDU (Richard Ohran)
Newsgroups: comp.sys.transputer
Subject: Re:  Dynamically determining memory size
Message-ID: <9001180030.AA27876@adam.byu.edu>
Date: 18 Jan 90 00:30:15 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 44

Here is a procedure written in Modula-2 which finds all the memory
between the top of the process and the top of memory.
It returns the starting address in the variable "adr" and the
number of available bytes in "size". It checks for both
memory wraparound and non-existent memory address regions.
 
 
PROCEDURE Allocate(VAR adr: POINTER TO BITSET; VAR size: CARDINAL);
 
  VAR x: POINTER TO ProcessState; 
      z,zchanged:BITSET;
      b:POINTER TO BITSET;
BEGIN (*size is in bytes*)
  InitProcessPtr(x);
  adr:=x^.ProcessTop;    (* adr now has the first memory address above
                           the running program*)
  size:=0;
  LOOP
    INC(adr,200H);
    b:=CARDINAL(adr) MOD 10000H + 80000000H; (*creating wraparound address*)
    IF adr^=b^ THEN (*potential memory wraparound*)
      z:=adr^;
      zchanged:=z/{0..31}; (*exclusive or*)
      adr^:=zchanged;
      IF adr^=b^ THEN (*wraparound*)
        adr^:=z;
        EXIT
      END
    END;
    (*now check for non-existent memory*)
    z:=adr^;
    z:=z/{0..31}; (* exclusive or*)
    adr^:=z;
    IF adr^<>z THEN EXIT END;
    adr^:= z/{0..31};(*restore data for valid word*)
    INC(size,200H);
  END;
  adr:=x^.ProcessTop;
END Allocate;
 
Hope this helps. If you have any questions about how it
works, call me at 801-226-8978.
 
Richard Ohran