DELPHI写的循环队列

unit cirstream;

interface

uses Windows, Classes, SysUtils;

type
  TCircleMemStream = Class(TObject)
  private
    FMemory: PChar;
    FCapacity: integer;
    ReadPosition: integer;
    WritePosition: integer;
  public
    constructor Create(BufferSize: integer);
    destructor Destroy; override;
//    function NextPosition();
    function Read(Buffer: PChar; Count: Longint): Longint;
    function Write(Buffer: PChar; Count: Longint): Longint;
    function DataSize(): integer;
  end;

implementation

constructor TCircleMemStream.Create(BufferSize: integer);
begin
  FCapacity := 1;
  while BufferSize <> 1 do
  begin
    FCapacity := FCapacity shl 1;
    BufferSize := BufferSize shr 1;
  end;
  GetMem(FMemory, FCapacity);
  ReadPosition := 0;
  WritePosition := 0;
end;

destructor TCircleMemStream.Destroy;
begin
  FreeMem(FMemory);
end;

function TCircleMemStream.Read(Buffer: PChar; Count: Longint): Longint;
var
  Mask: integer;
  roff: integer;
  readsize: integer;
begin
  Mask := FCapacity - 1;
  Result := 0;
  roff := 0;


  while (ReadPosition <> WritePosition) and (Count > 0) do
  begin
    if WritePosition > ReadPosition then
      readsize := WritePosition - ReadPosition
    else
      readsize := FCapacity - ReadPosition;
    if readsize > Count then
      readsize := Count;
    MoveMemory(@Buffer[roff], @FMemory[ReadPosition], readsize);
    Dec(Count, readsize);
    Inc(roff, readsize);
    Inc(Result, readsize);
    ReadPosition := (ReadPosition + readsize) and Mask;


  end;
end;

function TCircleMemStream.Write(Buffer: PChar; Count: Longint): Longint;
var
  Mask: integer;
  writesize: integer;
  woff: integer;
begin
  Mask := FCapacity - 1;
  Result := 0;
  woff := 0;

  writesize := (ReadPosition - WritePosition - 1) and Mask; //允许写入的大小
  while (writesize > 0) and (Count > 0) do
  begin
    if ReadPosition <= WritePosition then
    begin
      writesize := FCapacity - WritePosition;
      if ReadPosition = 0 then
        Dec(writesize, 1);
    end;
    if writesize > Count then
      writesize := Count;
    MoveMemory(@FMemory[WritePosition], @Buffer[woff], writesize);
    Dec(Count, writesize);
    Inc(woff, writesize);
    Inc(Result, writesize);
    WritePosition := WritePosition + writesize and Mask;

    writesize := (ReadPosition - WritePosition - 1) and Mask; //允许写入的大小
  end;

end;

function TCircleMemStream.DataSize(): integer;
var
  Mask: integer;
begin
  Mask := FCapacity - 1;
  Result := (WritePosition - ReadPosition) and Mask;
end;

end.