Date: 11/25/2000
Versions: VB5 VB6 Level: Intermediate
Author: Ernest Bayazitov 
 
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&

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