-- file VirtCom.mesa
-- edited by Kierr, February 8, 1978  11:32 AM.
-- edited by Schroeder, November 18, 1980  12:50 PM.
-- edited by Brotz, January 28, 1983  1:58 PM.
-- edited by Levin, November 19, 1980  10:15 AM.

DIRECTORY
  exD: FROM "ExceptionDefs" USING [SysBug],
  Inline USING [DIVMOD],
  tfD: FROM "TempFileDefs" USING [AllocateTempFile],
  vmD: FROM "VirtualMgrDefs" USING [CharCache, CharIndex, ComposedMessagePtr,
    MapCharIndexToPageByte, PageNumber, SetGetCacheForCMPage, VirtualMessagePtr,
    VirtualObjectPtr],
  VMDefs USING [Mark, MarkStart, PageNumber, ReadPage, Release, RemapPage,
    UsePage];

VirtCom: PROGRAM
  IMPORTS exD, Inline, tfD, vmD, VMDefs
  EXPORTS vmD =

BEGIN
OPEN vmD;


GetMessageChar: PUBLIC PROCEDURE [vm: VirtualMessagePtr, index: CharIndex]
  RETURNS [CHARACTER] =
-- Obtains the index'th character (starting at zero) from the virtual structure vs.
BEGIN
page: PageNumber;
byte: CARDINAL;
IF index ~IN [vm.get.first .. vm.get.free) THEN
  WITH msg: vm SELECT FROM
    DM =>
      BEGIN
      IF index >= msg.textLength THEN exD.SysBug[];
      [page, byte] _ Inline.DIVMOD[msg.firstByte + index, 512];
      page _ page + msg.firstPage;
      GetBuffer[vm, page, FALSE];
      vm.get.first _ IF index > byte THEN index - byte ELSE 0;
      vm.get.floor _ IF vm.get.first = 0 THEN byte - index ELSE 0;
      vm.get.free _ MIN[index + 512 - byte, vm.textLength];
      END;
    CM =>
      BEGIN
      [page, byte] _ MapCharIndexToPageByte[@msg, index];
      SetGetCacheForCMPage[@msg, page, index - byte, FALSE, TRUE];
      END;
    ENDCASE;
RETURN[vm.buffer.chars[index + vm.get.floor - vm.get.first]];
END; -- of GetMessageChar --


PutMessageChar: PUBLIC PROCEDURE
  [vm: VirtualMessagePtr, index: CharIndex, char: CHARACTER] =
-- The character at position index is overwritten with char.
BEGIN
IF index ~IN [vm.get.first .. vm.get.free) THEN [] _ GetMessageChar[vm, index];
vm.buffer.chars[index + vm.get.floor- vm.get.first] _ char;
vm.bufferState _ dirty;
END; -- of PutMessageChar --


VoidCharCache: PUBLIC PROCEDURE [c: POINTER TO CharCache] =
BEGIN
easyToSpotValue: CharIndex = 177777B;
c.first _ c.free _ easyToSpotValue; -- first=free is what counts
END; -- of VoidCharCache --


GetBuffer: PUBLIC PROCEDURE
  [vop: VirtualObjectPtr, pn: PageNumber, newPage: BOOLEAN] =
-- Obtains a buffer for page number "pn" of "vop".  If "pageState" = new, then a new
--   page is created at this "pn" (it better be the last page).  If "pageState" = old, then
--   existing page "pn" is read from vop's file.
BEGIN
IF ~newPage AND vop.bufferState # empty AND vop.logicalPageNumber = pn
  THEN RETURN;
IF vop.bufferState # empty THEN MakeBufferEmpty[vop];
vop.bufferState _ clean;
vop.logicalPageNumber _ pn;
vop.buffer _ IF newPage
  THEN VMDefs.UsePage[[vop.file, pn]]
  ELSE VMDefs.ReadPage[[vop.file, pn], 2];
END; -- of GetBuffer --


MakeBufferEmpty: PUBLIC PROCEDURE [vop: VirtualObjectPtr] =
-- Writes the buffer associated with "vop" if dirty.
BEGIN
SELECT vop.bufferState FROM
  empty => RETURN;
  dirty =>
    WITH msg: vop SELECT FROM
      VMO =>
        WITH cm: msg SELECT FROM
          CM => {EnsureCMBackingFile[@cm]; VMDefs.Mark[vop.buffer]};
          ENDCASE => VMDefs.MarkStart[vop.buffer];
      ENDCASE => VMDefs.MarkStart[vop.buffer];
  ENDCASE;
VMDefs.Release[vop.buffer];
vop.bufferState _ empty;
END; -- of MakeBufferEmpty --


EnsureCMBackingFile: PUBLIC PROCEDURE [cm: ComposedMessagePtr] =
-- Slides a backing file under the cm when needed.
BEGIN
IF cm.file = NIL THEN
  BEGIN
  cm.file _ tfD.AllocateTempFile[];
  IF cm.bufferState # empty THEN
    BEGIN
    IF cm.logicalPageNumber > 0 THEN exD.SysBug[];
    VMDefs.RemapPage[cm.buffer, [cm.file, cm.logicalPageNumber]];
    END;
  END;
END;  -- of EnsureCMBackingFile --


END.  -- of VirtCom --z19932(529)\f1