-- Transport Mechanism:  support for B-Tree package

-- [Juniper]<DMS>MS>BTreeSupport.mesa

-- Randy Gobbel		19-May-81 21:20:17
-- Andrew Birrell	 2-Sep-80 14:38:22


DIRECTORY
  BTreeSupportDefs	USING[FileHandle, PageHandle, PageNumber],
  Storage		USING[Free, Node],
  VMDefs		USING[GetFileLength, Mark, PageAddress, pageSize,
			      ReadPage, Release, RemapPage, SetFileLength, UsePage];


BTreeSupport: PROGRAM

IMPORTS Storage, VMDefs
EXPORTS BTreeSupportDefs =

BEGIN

ReadPage: PUBLIC PROCEDURE[fileH: BTreeSupportDefs.FileHandle,
                           pageN: BTreeSupportDefs.PageNumber]
                  RETURNS [pageH: BTreeSupportDefs.PageHandle] =
   BEGIN
   addr: VMDefs.PageAddress = [file: LOOPHOLE[fileH], page: pageN];
   RETURN[ LOOPHOLE[ VMDefs.ReadPage[addr, 0--lookAhead--] ] ]
   END;

UsePage: PUBLIC PROCEDURE[fileH: BTreeSupportDefs.FileHandle,
                          pageN: BTreeSupportDefs.PageNumber]
                 RETURNS [pageH: BTreeSupportDefs.PageHandle] =
   BEGIN
   addr: VMDefs.PageAddress = [file: LOOPHOLE[fileH], page: pageN];
   pageH _ LOOPHOLE[ VMDefs.UsePage[addr] ];
   IF addr.page = VMDefs.GetFileLength[addr.file].page
   THEN VMDefs.SetFileLength[addr.file, [page:addr.page+1, byte:0] ];
   END;

WritePage: PUBLIC PROCEDURE[fileH: BTreeSupportDefs.FileHandle,
                            pageN: BTreeSupportDefs.PageNumber,
                            pageH: BTreeSupportDefs.PageHandle] =
   BEGIN
   addr: VMDefs.PageAddress = [file: LOOPHOLE[fileH], page: pageN];
   VMDefs.RemapPage[LOOPHOLE[pageH], addr];
   VMDefs.Mark[LOOPHOLE[pageH]];
   VMDefs.Release[LOOPHOLE[pageH]];
   END;

ReleasePage: PUBLIC PROCEDURE[pageH: BTreeSupportDefs.PageHandle] =
   BEGIN
   VMDefs.Release[LOOPHOLE[pageH]];
   END;

SetLength: PUBLIC PROCEDURE[fileH: BTreeSupportDefs.FileHandle,
                            pageN: BTreeSupportDefs.PageNumber] =
   BEGIN
   addr: VMDefs.PageAddress = [file: LOOPHOLE[fileH], page: pageN];
   VMDefs.SetFileLength[addr.file, [page:addr.page, byte:0] ];
   END;

PageSize: PUBLIC PROCEDURE RETURNS[nWords: CARDINAL] =
   BEGIN
   RETURN[ VMDefs.pageSize ]
   END;

AllocateWords: PUBLIC PROCEDURE[nWords: CARDINAL] RETURNS[POINTER] =
   BEGIN
   RETURN[Storage.Node[nWords]];
   END;

FreeWords: PUBLIC PROCEDURE[pntr: POINTER] =
   BEGIN
   Storage.Free[pntr];
   END;

END.