Binaryworld - Crc16 - Evaluate the 16-bit CRC of an array of bytes ... [ VB -> Math ]

Option Explicit

' Evalutate the 16-bit CRC (Cyclic Redundancy Checksum) of an array of bytes
'
' If you omit the second argument, the entire array is considered

Function Crc16(cp() As Byte, Optional ByVal Size As Long = -1) As Long
Dim i As Long
Dim fcs As Long
Static fcstab(255) As Long

Const pppinitfcs16 = &HFFFF& 'Initial FCS value

If Size < 0 Then Size = UBound(cp) - LBound(cp) + 1

If fcstab(1) = 0 Then
  ' Initialize array once and for all
  fcstab(0) = &H0&
  fcstab(1) = &H1189&
  fcstab(2) = &H2312&
  fcstab(3) = &H329B&
  fcstab(4) = &H4624&
  fcstab(5) = &H57AD&
  fcstab(6) = &H6536&
  fcstab(7) = &H74BF&
  fcstab(8) = &H8C48&
  fcstab(9) = &H9DC1&
  fcstab(10) = &HAF5A&
  fcstab(11) = &HBED3&
  fcstab(12) = &HCA6C&
  fcstab(13) = &HDBE5&
  fcstab(14) = &HE97E&
  fcstab(15) = &HF8F7&
  fcstab(16) = &H1081&
  fcstab(17) = &H108&
  fcstab(18) = &H3393&
  fcstab(19) = &H221A&
  fcstab(20) = &H56A5&
  fcstab(21) = &H472C&
  fcstab(22) = &H75B7&
  fcstab(23) = &H643E&
  fcstab(24) = &H9CC9&
  fcstab(25) = &H8D40&
  fcstab(26) = &HBFDB&
  fcstab(27) = &HAE52&
  fcstab(28) = &HDAED&
  fcstab(29) = &HCB64&
  fcstab(30) = &HF9FF&
  fcstab(31) = &HE876&
  fcstab(32) = &H2102&
  fcstab(33) = &H308B&
  fcstab(34) = &H210&
  fcstab(35) = &H1399&
  fcstab(36) = &H6726&
  fcstab(37) = &H76AF&
  fcstab(38) = &H4434&
  fcstab(39) = &H55BD&
  fcstab(40) = &HAD4A&
  fcstab(41) = &HBCC3&
  fcstab(42) = &H8E58&
  fcstab(43) = &H9FD1&
  fcstab(44) = &HEB6E&
  fcstab(45) = &HFAE7&
  fcstab(46) = &HC87C&
  fcstab(47) = &HD9F5&
  fcstab(48) = &H3183&
  fcstab(49) = &H200A&
  fcstab(50) = &H1291&
  fcstab(51) = &H318&
  fcstab(52) = &H77A7&
  fcstab(53) = &H662E&
  fcstab(54) = &H54B5&
  fcstab(55) = &H453C&
  fcstab(56) = &HBDCB&
  fcstab(57) = &HAC42&
  fcstab(58) = &H9ED9&
  fcstab(59) = &H8F50&
  fcstab(60) = &HFBEF&
  fcstab(61) = &HEA66&
  fcstab(62) = &HD8FD&
  fcstab(63) = &HC974&
  fcstab(64) = &H4204&
  fcstab(65) = &H538D&
  fcstab(66) = &H6116&
  fcstab(67) = &H709F&
  fcstab(68) = &H420&
  fcstab(69) = &H15A9&
  fcstab(70) = &H2732&
  fcstab(71) = &H36BB&
  fcstab(72) = &HCE4C&
  fcstab(73) = &HDFC5&
  fcstab(74) = &HED5E&
  fcstab(75) = &HFCD7&
  fcstab(76) = &H8868&
  fcstab(77) = &H99E1&
  fcstab(78) = &HAB7A&
  fcstab(79) = &HBAF3&
  fcstab(80) = &H5285&
  fcstab(81) = &H430C&
  fcstab(82) = &H7197&
  fcstab(83) = &H601E&
  fcstab(84) = &H14A1&
  fcstab(85) = &H528&
  fcstab(86) = &H37B3&
  fcstab(87) = &H263A&
  fcstab(88) = &HDECD&
  fcstab(89) = &HCF44&
  fcstab(90) = &HFDDF&
  fcstab(91) = &HEC56&
  fcstab(92) = &H98E9&
  fcstab(93) = &H8960&
  fcstab(94) = &HBBFB&
  fcstab(95) = &HAA72&
  fcstab(96) = &H6306&
  fcstab(97) = &H728F&
  fcstab(98) = &H4014&
  fcstab(99) = &H519D&
  fcstab(100) = &H2522&
  fcstab(101) = &H34AB&
  fcstab(102) = &H630&
  fcstab(103) = &H17B9&
  fcstab(104) = &HEF4E&
  fcstab(105) = &HFEC7&
  fcstab(106) = &HCC5C&
  fcstab(107) = &HDDD5&
  fcstab(108) = &HA96A&
  fcstab(109) = &HB8E3&
  fcstab(110) = &H8A78&
  fcstab(111) = &H9BF1&
  fcstab(112) = &H7387&
  fcstab(113) = &H620E&
  fcstab(114) = &H5095&
  fcstab(115) = &H411C&
  fcstab(116) = &H35A3&
  fcstab(117) = &H242A&
  fcstab(118) = &H16B1&
  fcstab(119) = &H738&
  fcstab(120) = &HFFCF&
  fcstab(121) = &HEE46&
  fcstab(122) = &HDCDD&
  fcstab(123) = &HCD54&
  fcstab(124) = &HB9EB&
  fcstab(125) = &HA862&
  fcstab(126) = &H9AF9&
  fcstab(127) = &H8B70&
  fcstab(128) = &H8408&
  fcstab(129) = &H9581&
  fcstab(130) = &HA71A&
  fcstab(131) = &HB693&
  fcstab(132) = &HC22C&
  fcstab(133) = &HD3A5&
  fcstab(134) = &HE13E&
  fcstab(135) = &HF0B7&
  fcstab(136) = &H840&
  fcstab(137) = &H19C9&
  fcstab(138) = &H2B52&
  fcstab(139) = &H3ADB&
  fcstab(140) = &H4E64&
  fcstab(141) = &H5FED&
  fcstab(142) = &H6D76&
  fcstab(143) = &H7CFF&
  fcstab(144) = &H9489&
  fcstab(145) = &H8500&
  fcstab(146) = &HB79B&
  fcstab(147) = &HA612&
  fcstab(148) = &HD2AD&
  fcstab(149) = &HC324&
  fcstab(150) = &HF1BF&
  fcstab(151) = &HE036&
  fcstab(152) = &H18C1&
  fcstab(153) = &H948&
  fcstab(154) = &H3BD3&
  fcstab(155) = &H2A5A&
  fcstab(156) = &H5EE5&
  fcstab(157) = &H4F6C&
  fcstab(158) = &H7DF7&
  fcstab(159) = &H6C7E&
  fcstab(160) = &HA50A&
  fcstab(161) = &HB483&
  fcstab(162) = &H8618&
  fcstab(163) = &H9791&
  fcstab(164) = &HE32E&
  fcstab(165) = &HF2A7&
  fcstab(166) = &HC03C&
  fcstab(167) = &HD1B5&
  fcstab(168) = &H2942&
  fcstab(169) = &H38CB&
  fcstab(170) = &HA50&
  fcstab(171) = &H1BD9&
  fcstab(172) = &H6F66&
  fcstab(173) = &H7EEF&
  fcstab(174) = &H4C74&
  fcstab(175) = &H5DFD&
  fcstab(176) = &HB58B&
  fcstab(177) = &HA402&
  fcstab(178) = &H9699&
  fcstab(179) = &H8710&
  fcstab(180) = &HF3AF&
  fcstab(181) = &HE226&
  fcstab(182) = &HD0BD&
  fcstab(183) = &HC134&
  fcstab(184) = &H39C3&
  fcstab(185) = &H284A&
  fcstab(186) = &H1AD1&
  fcstab(187) = &HB58&
  fcstab(188) = &H7FE7&
  fcstab(189) = &H6E6E&
  fcstab(190) = &H5CF5&
  fcstab(191) = &H4D7C&
  fcstab(192) = &HC60C&
  fcstab(193) = &HD785&
  fcstab(194) = &HE51E&
  fcstab(195) = &HF497&
  fcstab(196) = &H8028&
  fcstab(197) = &H91A1&
  fcstab(198) = &HA33A&
  fcstab(199) = &HB2B3&
  fcstab(200) = &H4A44&
  fcstab(201) = &H5BCD&
  fcstab(202) = &H6956&
  fcstab(203) = &H78DF&
  fcstab(204) = &HC60&
  fcstab(205) = &H1DE9&
  fcstab(206) = &H2F72&
  fcstab(207) = &H3EFB&
  fcstab(208) = &HD68D&
  fcstab(209) = &HC704&
  fcstab(210) = &HF59F&
  fcstab(211) = &HE416&
  fcstab(212) = &H90A9&
  fcstab(213) = &H8120&
  fcstab(214) = &HB3BB&
  fcstab(215) = &HA232&
  fcstab(216) = &H5AC5&
  fcstab(217) = &H4B4C&
  fcstab(218) = &H79D7&
  fcstab(219) = &H685E&
  fcstab(220) = &H1CE1&
  fcstab(221) = &HD68&
  fcstab(222) = &H3FF3&
  fcstab(223) = &H2E7A&
  fcstab(224) = &HE70E&
  fcstab(225) = &HF687&
  fcstab(226) = &HC41C&
  fcstab(227) = &HD595&
  fcstab(228) = &HA12A&
  fcstab(229) = &HB0A3&
  fcstab(230) = &H8238&
  fcstab(231) = &H93B1&
  fcstab(232) = &H6B46&
  fcstab(233) = &H7ACF&
  fcstab(234) = &H4854&
  fcstab(235) = &H59DD&
  fcstab(236) = &H2D62&
  fcstab(237) = &H3CEB&
  fcstab(238) = &HE70&
  fcstab(239) = &H1FF9&
  fcstab(240) = &HF78F&
  fcstab(241) = &HE606&
  fcstab(242) = &HD49D&
  fcstab(243) = &HC514&
  fcstab(244) = &HB1AB&
  fcstab(245) = &HA022&
  fcstab(246) = &H92B9&
  fcstab(247) = &H8330&
  fcstab(248) = &H7BC7&
  fcstab(249) = &H6A4E&
  fcstab(250) = &H58D5&
  fcstab(251) = &H495C&
  fcstab(252) = &H3DE3&
  fcstab(253) = &H2C6A&
  fcstab(254) = &H1EF1&
  fcstab(255) = &HF78&
End If

' The initial FCS value
fcs = pppinitfcs16

' evaluate the FCS
For i = LBound(cp) To LBound(cp) + Size - 1
  fcs = (fcs \ &H100&) Xor fcstab((fcs Xor cp(i)) And &HFF&)
Next i

' return the result
Crc16 = fcs
End Function