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Unit FCache;
interface
{ ---------------------- File Cache -------------------------- }
{ implements a simple file cache and mimic C getc and ungetc
functions. }
const
BufMemSize = 4096;
EOF = ^Z;
type
Cache = record
active : boolean;
BildOffset : LongInt;
Buffer : array[0..BufMemSize-1] of byte;
FVarPtr : ^file;
FileOfs : LongInt;
BufPos : integer;
BufSize : integer;
end;
Procedure fc_Init(var fc : Cache;
var f : file; FPos : LongInt);
Procedure fc_Close(var fc : Cache);
Procedure fc_Done(var fc : Cache;
var f : file);
Procedure fc_ReadBlock(var fc : Cache);
Function fc_getc(var fc : Cache) : Byte;
{ Read a byte at the current buffer read-index, increment the buffer
read-index }
function fc_ungetc (var fc : Cache; ch : char) : Byte;
{ Read a byte at the current buffer read-index, increment the buffer
read-index }
procedure fc_WriteTo(var fc : Cache;
var Buf; Count : Word);
implementation
{$IFDEF USE_DOS}
uses
Dos;
{$ENDIF}
Procedure fc_Init(var fc : Cache;
var f : file; FPos : LongInt);
begin
with fc do
begin
active := false;
FVarPtr := @f;
FileOfs := FPos;
BufSize := 0;
BufPos := 0;
{$IFDEF USE_DOS}
if TFileRec(f).Mode <> fmClosed then
{$ENDIF}
begin
{$IFOPT I+} {$DEFINE IOCheck} {$I-} {$ENDIF}
Seek(f, FPos);
BlockRead(f, Buffer, BufMemSize, BufSize);
{$IFDEF IOCheck} {$I+} {$ENDIF}
if (IOResult = 0) and (BufSize <> 0) then
active := true;
end;
end;
end;
Procedure fc_Done(var fc : Cache;
var f : file);
begin
with fc do
if FVarPtr = @f then
begin
active := false;
FVarPtr := NIL;
FileOfs := 0;
BufSize := 0;
BufPos := 0;
end;
end;
Procedure fc_Close(var fc : Cache);
begin
with fc do
begin
if Assigned(FVarPtr) then
Close(FVarPtr^);
fc_Done(fc, FVarPtr^);
end;
end;
Procedure fc_ReadBlock(var fc : Cache);
Begin
with fc do
if active then
begin
{$I-}
Seek(FVarPtr^, FileOfs);
BlockRead(FVarPtr^, Buffer, BufMemSize, BufSize);
{$IFDEF IOCheck} {$I+} {$ENDIF}
BufPos := 0;
active := (IOResult = 0) and (BufSize <> 0);
end;
End;
Function fc_getc(var fc : Cache) : Byte;
{ Read a byte at the current buffer read-index, increment the buffer
read-index }
begin
with fc do
if active then
begin
fc_GetC := Buffer[BufPos];
Inc(BufPos);
if BufPos = BufSize then
begin
Inc(FileOfs, BufSize);
fc_ReadBlock(fc);
end;
end
else
fc_getc := Byte(EOF);
end;
function fc_ungetc (var fc : Cache; ch : char) : Byte;
{ Read a byte at the current buffer read-index, increment the buffer
read-index }
begin
with fc do
begin
fc_UnGetC := Byte(EOF);
if active and (FileOfs > 0) then
begin
if BufPos = 0 then
begin
Dec(FileOfs);
fc_ReadBlock(fc);
end;
if BufPos > 0 then
begin
Dec(BufPos);
fc_UnGetC := Buffer[BufPos];
end;
end;
end;
end;
procedure fc_WriteTo(var fc : Cache;
var Buf; Count : Word);
type
PByte = ^Byte;
var
ChunkSize : Word;
DestPtr : PByte;
Begin
with fc do
if active then
begin
ChunkSize := BufSize - BufPos;
DestPtr := PByte(@Buf);
if Count > ChunkSize then
begin
{ the amount we need to read straddles a buffer boundary,
we need two or more chunks. This implementation doesn't try
to read more than two chunks. }
Move(Buffer[BufPos], Buf, ChunkSize);
Inc(DestPtr, ChunkSize);
Dec(count, ChunkSize);
Inc(FileOfs, BufSize);
fc_ReadBlock(fc);
end;
{ we are now completely within the buffer boundary,
do a simple mem move }
Move(Buffer[BufPos], DestPtr^, count);
end;
End;
{ ---------------------- End File Cache -------------------------- }
end.
|
