Delphi ModbusCRC16校验

huaiying

{===============================================================================
@ CRC16校验生成函数
===============================================================================}
function Crc16Check(Buff : array of Byte; Len : Integer):short;
const
  CrcHighBlock : array[0..255] of Byte = (
    $00, $C1, $81, $40, $01, $C0, $80, $41, $01, $C0, $80, $41, $00, $C1, $81, $40,
    $01, $C0, $80, $41, $00, $C1, $81, $40, $00, $C1, $81, $40, $01, $C0, $80, $41,
    $01, $C0, $80, $41, $00, $C1, $81, $40, $00, $C1, $81, $40, $01, $C0, $80, $41,
    $00, $C1, $81, $40, $01, $C0, $80, $41, $01, $C0, $80, $41, $00, $C1, $81, $40,
    $01, $C0, $80, $41, $00, $C1, $81, $40, $00, $C1, $81, $40, $01, $C0, $80, $41,
    $00, $C1, $81, $40, $01, $C0, $80, $41, $01, $C0, $80, $41, $00, $C1, $81, $40,
    $00, $C1, $81, $40, $01, $C0, $80, $41, $01, $C0, $80, $41, $00, $C1, $81, $40,
    $01, $C0, $80, $41, $00, $C1, $81, $40, $00, $C1, $81, $40, $01, $C0, $80, $41,
    $01, $C0, $80, $41, $00, $C1, $81, $40, $00, $C1, $81, $40, $01, $C0, $80, $41,
    $00, $C1, $81, $40, $01, $C0, $80, $41, $01, $C0, $80, $41, $00, $C1, $81, $40,
    $00, $C1, $81, $40, $01, $C0, $80, $41, $01, $C0, $80, $41, $00, $C1, $81, $40,
    $01, $C0, $80, $41, $00, $C1, $81, $40, $00, $C1, $81, $40, $01, $C0, $80, $41,
    $00, $C1, $81, $40, $01, $C0, $80, $41, $01, $C0, $80, $41, $00, $C1, $81, $40,
    $01, $C0, $80, $41, $00, $C1, $81, $40, $00, $C1, $81, $40, $01, $C0, $80, $41,
    $01, $C0, $80, $41, $00, $C1, $81, $40, $00, $C1, $81, $40, $01, $C0, $80, $41,
    $00, $C1, $81, $40, $01, $C0, $80, $41, $01, $C0, $80, $41, $00, $C1, $81, $40
  );

  CrcLowBlock : array[0..255] of Byte=(
    $00, $C0, $C1, $01, $C3, $03, $02, $C2, $C6, $06, $07, $C7, $05, $C5, $C4, $04,
    $CC, $0C, $0D, $CD, $0F, $CF, $CE, $0E, $0A, $CA, $CB, $0B, $C9, $09, $08, $C8,
    $D8, $18, $19, $D9, $1B, $DB, $DA, $1A, $1E, $DE, $DF, $1F, $DD, $1D, $1C, $DC,
    $14, $D4, $D5, $15, $D7, $17, $16, $D6, $D2, $12, $13, $D3, $11, $D1, $D0, $10,
    $F0, $30, $31, $F1, $33, $F3, $F2, $32, $36, $F6, $F7, $37, $F5, $35, $34, $F4,
    $3C, $FC, $FD, $3D, $FF, $3F, $3E, $FE, $FA, $3A, $3B, $FB, $39, $F9, $F8, $38,
    $28, $E8, $E9, $29, $EB, $2B, $2A, $EA, $EE, $2E, $2F, $EF, $2D, $ED, $EC, $2C,
    $E4, $24, $25, $E5, $27, $E7, $E6, $26, $22, $E2, $E3, $23, $E1, $21, $20, $E0,
    $A0, $60, $61, $A1, $63, $A3, $A2, $62, $66, $A6, $A7, $67, $A5, $65, $64, $A4,
    $6C, $AC, $AD, $6D, $AF, $6F, $6E, $AE, $AA, $6A, $6B, $AB, $69, $A9, $A8, $68,
    $78, $B8, $B9, $79, $BB, $7B, $7A, $BA, $BE, $7E, $7F, $BF, $7D, $BD, $BC, $7C,
    $B4, $74, $75, $B5, $77, $B7, $B6, $76, $72, $B2, $B3, $73, $B1, $71, $70, $B0,
    $50, $90, $91, $51, $93, $53, $52, $92, $96, $56, $57, $97, $55, $95, $94, $54,
    $9C, $5C, $5D, $9D, $5F, $9F, $9E, $5E, $5A, $9A, $9B, $5B, $99, $59, $58, $98,
    $88, $48, $49, $89, $4B, $8B, $8A, $4A, $4E, $8E, $8F, $4F, $8D, $4D, $4C, $8C,
    $44, $84, $85, $45, $87, $47, $46, $86, $82, $42, $43, $83, $41, $81, $80, $40
  );
var
  hight : Byte;
  low   : Byte;
  index : Byte;
  i     : integer;
  Check : short;
begin
  hight := $ff;
  low   := $ff;

  for i := 0 to len - 1 do begin
    index := hight xor Buff[i];
    hight := low xor CrcHighBlock[index];
    low   := CrcLowBlock[index];
  end;

  Check := hight;
  Check := (Check shl 8) or low;
  result := Check;
end;