Attribute VB_Name = "modCRC32"
'CRC Checksum Class
'------------------------------------
'
'A very fast solution to calculate the
'CRC Checksum (CRC32) with the help of
'some pre-compiled assembler code
'
'(c) 2000, Fredrik Qvarfort

Option Explicit

Private m_CRC32 As Long
Private m_CRC32Asm() As Byte
'Private m_CRC32Init As Boolean
Private m_CRC32Table(0 To 255) As Long

Private Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" (ByVal lpPrevWndFunc As Long, ByVal hWnd As Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long

Public Function AddBytes(ByteArray() As Byte) As Long
  Dim ByteSize As Long
  
  'We need to add a simple error trapping
  'here because if the bytearray is not
  'dimensioned we want it to just skip
  'the assembler code call below
  On Local Error GoTo NoData
  
  'Precalculate the size of the byte array
  ByteSize = UBound(ByteArray) - LBound(ByteArray) + 1
  
  'No error trapping needed, if something
  'goes bad below something is definitely
  'fishy with your computer
  On Local Error GoTo 0
  
  'Run the pre-compiled assembler code
  Call CallWindowProc(VarPtr(m_CRC32Asm(0)), VarPtr(m_CRC32), VarPtr(ByteArray(LBound(ByteArray))), VarPtr(m_CRC32Table(0)), ByteSize)
  
NoData:
  'Return the current CRC value
  AddBytes = Value
End Function

'Public Function AddString(Text As String) As Variant
'  'Convert the string into a byte array
'  'and send it to the function that can
'  'handle bytearrays
'  AddString = AddBytes(StrConv(Text, vbFromUnicode))
'End Function

Public Function CalculateBytes(ByteArray() As Byte) As Long
  'Reset the current CRC calculation
  Call Clear
  
  'Calculate the CRC from the bytearray
  'and return the current CRC value
  CalculateBytes = AddBytes(ByteArray)
End Function

Public Function CalculateFile(Filename As String) As Long
  Dim Filenr As Integer
  Dim ByteArray() As Byte
  
  'Make sure the file contains data
  'to avoid errors later below
  If (FileLen(Filename) = 0) Then Exit Function
  
  'Open the file in binary mode, read
  'the data into a bytearray and then
  'close the file
  Filenr = FreeFile
  Open Filename For Binary As #Filenr
  ReDim ByteArray(0 To LOF(Filenr) - 1)
  Get #Filenr, , ByteArray()
  Close #Filenr
  
  'Now send the bytearray to the function
  'that can calculate a CRC from it
  CalculateFile = CalculateBytes(ByteArray)
End Function

'Public Function CalculateString(Text As String)
'  'Convert the string into a bytearray
'  'and send it to the function that
'  'calculates the CRC from a bytearray
'  CalculateString = CalculateBytes(StrConv(Text, vbFromUnicode))
'End Function

Private Function Value() As Long
    Value = (Not m_CRC32)
End Function

'Public Property Get Value() As Variant
'    Value = (Not m_CRC32)
'End Property

'Public Property Let Value(New_Value As Variant)
'    m_CRC32 = New_Value
'End Property

Public Sub Clear()
  'reset crc variable
  m_CRC32 = &HFFFFFFFF
End Sub

Public Sub InitializeCRC32()
  Dim i As Long
  Dim sASM As String
  
  m_CRC32Table(0) = &H0
  m_CRC32Table(1) = &H77073096
  m_CRC32Table(2) = &HEE0E612C
  m_CRC32Table(3) = &H990951BA
  m_CRC32Table(4) = &H76DC419
  m_CRC32Table(5) = &H706AF48F
  m_CRC32Table(6) = &HE963A535
  m_CRC32Table(7) = &H9E6495A3
  m_CRC32Table(8) = &HEDB8832
  m_CRC32Table(9) = &H79DCB8A4
  m_CRC32Table(10) = &HE0D5E91E
  m_CRC32Table(11) = &H97D2D988
  m_CRC32Table(12) = &H9B64C2B
  m_CRC32Table(13) = &H7EB17CBD
  m_CRC32Table(14) = &HE7B82D07
  m_CRC32Table(15) = &H90BF1D91
  m_CRC32Table(16) = &H1DB71064
  m_CRC32Table(17) = &H6AB020F2
  m_CRC32Table(18) = &HF3B97148
  m_CRC32Table(19) = &H84BE41DE
  m_CRC32Table(20) = &H1ADAD47D
  m_CRC32Table(21) = &H6DDDE4EB
  m_CRC32Table(22) = &HF4D4B551
  m_CRC32Table(23) = &H83D385C7
  m_CRC32Table(24) = &H136C9856
  m_CRC32Table(25) = &H646BA8C0
  m_CRC32Table(26) = &HFD62F97A
  m_CRC32Table(27) = &H8A65C9EC
  m_CRC32Table(28) = &H14015C4F
  m_CRC32Table(29) = &H63066CD9
  m_CRC32Table(30) = &HFA0F3D63
  m_CRC32Table(31) = &H8D080DF5
  m_CRC32Table(32) = &H3B6E20C8
  m_CRC32Table(33) = &H4C69105E
  m_CRC32Table(34) = &HD56041E4
  m_CRC32Table(35) = &HA2677172
  m_CRC32Table(36) = &H3C03E4D1
  m_CRC32Table(37) = &H4B04D447
  m_CRC32Table(38) = &HD20D85FD
  m_CRC32Table(39) = &HA50AB56B
  m_CRC32Table(40) = &H35B5A8FA
  m_CRC32Table(41) = &H42B2986C
  m_CRC32Table(42) = &HDBBBC9D6
  m_CRC32Table(43) = &HACBCF940
  m_CRC32Table(44) = &H32D86CE3
  m_CRC32Table(45) = &H45DF5C75
  m_CRC32Table(46) = &HDCD60DCF
  m_CRC32Table(47) = &HABD13D59
  m_CRC32Table(48) = &H26D930AC
  m_CRC32Table(49) = &H51DE003A
  m_CRC32Table(50) = &HC8D75180
  m_CRC32Table(51) = &HBFD06116
  m_CRC32Table(52) = &H21B4F4B5
  m_CRC32Table(53) = &H56B3C423
  m_CRC32Table(54) = &HCFBA9599
  m_CRC32Table(55) = &HB8BDA50F
  m_CRC32Table(56) = &H2802B89E
  m_CRC32Table(57) = &H5F058808
  m_CRC32Table(58) = &HC60CD9B2
  m_CRC32Table(59) = &HB10BE924
  m_CRC32Table(60) = &H2F6F7C87
  m_CRC32Table(61) = &H58684C11
  m_CRC32Table(62) = &HC1611DAB
  m_CRC32Table(63) = &HB6662D3D
  m_CRC32Table(64) = &H76DC4190
  m_CRC32Table(65) = &H1DB7106
  m_CRC32Table(66) = &H98D220BC
  m_CRC32Table(67) = &HEFD5102A
  m_CRC32Table(68) = &H71B18589
  m_CRC32Table(69) = &H6B6B51F
  m_CRC32Table(70) = &H9FBFE4A5
  m_CRC32Table(71) = &HE8B8D433
  m_CRC32Table(72) = &H7807C9A2
  m_CRC32Table(73) = &HF00F934
  m_CRC32Table(74) = &H9609A88E
  m_CRC32Table(75) = &HE10E9818
  m_CRC32Table(76) = &H7F6A0DBB
  m_CRC32Table(77) = &H86D3D2D
  m_CRC32Table(78) = &H91646C97
  m_CRC32Table(79) = &HE6635C01
  m_CRC32Table(80) = &H6B6B51F4
  m_CRC32Table(81) = &H1C6C6162
  m_CRC32Table(82) = &H856530D8
  m_CRC32Table(83) = &HF262004E
  m_CRC32Table(84) = &H6C0695ED
  m_CRC32Table(85) = &H1B01A57B
  m_CRC32Table(86) = &H8208F4C1
  m_CRC32Table(87) = &HF50FC457
  m_CRC32Table(88) = &H65B0D9C6
  m_CRC32Table(89) = &H12B7E950
  m_CRC32Table(90) = &H8BBEB8EA
  m_CRC32Table(91) = &HFCB9887C
  m_CRC32Table(92) = &H62DD1DDF
  m_CRC32Table(93) = &H15DA2D49
  m_CRC32Table(94) = &H8CD37CF3
  m_CRC32Table(95) = &HFBD44C65
  m_CRC32Table(96) = &H4DB26158
  m_CRC32Table(97) = &H3AB551CE
  m_CRC32Table(98) = &HA3BC0074
  m_CRC32Table(99) = &HD4BB30E2
  m_CRC32Table(100) = &H4ADFA541
  m_CRC32Table(101) = &H3DD895D7
  m_CRC32Table(102) = &HA4D1C46D
  m_CRC32Table(103) = &HD3D6F4FB
  m_CRC32Table(104) = &H4369E96A
  m_CRC32Table(105) = &H346ED9FC
  m_CRC32Table(106) = &HAD678846
  m_CRC32Table(107) = &HDA60B8D0
  m_CRC32Table(108) = &H44042D73
  m_CRC32Table(109) = &H33031DE5
  m_CRC32Table(110) = &HAA0A4C5F
  m_CRC32Table(111) = &HDD0D7CC9
  m_CRC32Table(112) = &H5005713C
  m_CRC32Table(113) = &H270241AA
  m_CRC32Table(114) = &HBE0B1010
  m_CRC32Table(115) = &HC90C2086
  m_CRC32Table(116) = &H5768B525
  m_CRC32Table(117) = &H206F85B3
  m_CRC32Table(118) = &HB966D409
  m_CRC32Table(119) = &HCE61E49F
  m_CRC32Table(120) = &H5EDEF90E
  m_CRC32Table(121) = &H29D9C998
  m_CRC32Table(122) = &HB0D09822
  m_CRC32Table(123) = &HC7D7A8B4
  m_CRC32Table(124) = &H59B33D17
  m_CRC32Table(125) = &H2EB40D81
  m_CRC32Table(126) = &HB7BD5C3B
  m_CRC32Table(127) = &HC0BA6CAD
  m_CRC32Table(128) = &HEDB88320
  m_CRC32Table(129) = &H9ABFB3B6
  m_CRC32Table(130) = &H3B6E20C
  m_CRC32Table(131) = &H74B1D29A
  m_CRC32Table(132) = &HEAD54739
  m_CRC32Table(133) = &H9DD277AF
  m_CRC32Table(134) = &H4DB2615
  m_CRC32Table(135) = &H73DC1683
  m_CRC32Table(136) = &HE3630B12
  m_CRC32Table(137) = &H94643B84
  m_CRC32Table(138) = &HD6D6A3E
  m_CRC32Table(139) = &H7A6A5AA8
  m_CRC32Table(140) = &HE40ECF0B
  m_CRC32Table(141) = &H9309FF9D
  m_CRC32Table(142) = &HA00AE27
  m_CRC32Table(143) = &H7D079EB1
  m_CRC32Table(144) = &HF00F9344
  m_CRC32Table(145) = &H8708A3D2
  m_CRC32Table(146) = &H1E01F268
  m_CRC32Table(147) = &H6906C2FE
  m_CRC32Table(148) = &HF762575D
  m_CRC32Table(149) = &H806567CB
  m_CRC32Table(150) = &H196C3671
  m_CRC32Table(151) = &H6E6B06E7
  m_CRC32Table(152) = &HFED41B76
  m_CRC32Table(153) = &H89D32BE0
  m_CRC32Table(154) = &H10DA7A5A
  m_CRC32Table(155) = &H67DD4ACC
  m_CRC32Table(156) = &HF9B9DF6F
  m_CRC32Table(157) = &H8EBEEFF9
  m_CRC32Table(158) = &H17B7BE43
  m_CRC32Table(159) = &H60B08ED5
  m_CRC32Table(160) = &HD6D6A3E8
  m_CRC32Table(161) = &HA1D1937E
  m_CRC32Table(162) = &H38D8C2C4
  m_CRC32Table(163) = &H4FDFF252
  m_CRC32Table(164) = &HD1BB67F1
  m_CRC32Table(165) = &HA6BC5767
  m_CRC32Table(166) = &H3FB506DD
  m_CRC32Table(167) = &H48B2364B
  m_CRC32Table(168) = &HD80D2BDA
  m_CRC32Table(169) = &HAF0A1B4C
  m_CRC32Table(170) = &H36034AF6
  m_CRC32Table(171) = &H41047A60
  m_CRC32Table(172) = &HDF60EFC3
  m_CRC32Table(173) = &HA867DF55
  m_CRC32Table(174) = &H316E8EEF
  m_CRC32Table(175) = &H4669BE79
  m_CRC32Table(176) = &HCB61B38C
  m_CRC32Table(177) = &HBC66831A
  m_CRC32Table(178) = &H256FD2A0
  m_CRC32Table(179) = &H5268E236
  m_CRC32Table(180) = &HCC0C7795
  m_CRC32Table(181) = &HBB0B4703
  m_CRC32Table(182) = &H220216B9
  m_CRC32Table(183) = &H5505262F
  m_CRC32Table(184) = &HC5BA3BBE
  m_CRC32Table(185) = &HB2BD0B28
  m_CRC32Table(186) = &H2BB45A92
  m_CRC32Table(187) = &H5CB36A04
  m_CRC32Table(188) = &HC2D7FFA7
  m_CRC32Table(189) = &HB5D0CF31
  m_CRC32Table(190) = &H2CD99E8B
  m_CRC32Table(191) = &H5BDEAE1D
  m_CRC32Table(192) = &H9B64C2B0
  m_CRC32Table(193) = &HEC63F226
  m_CRC32Table(194) = &H756AA39C
  m_CRC32Table(195) = &H26D930A
  m_CRC32Table(196) = &H9C0906A9
  m_CRC32Table(197) = &HEB0E363F
  m_CRC32Table(198) = &H72076785
  m_CRC32Table(199) = &H5005713
  m_CRC32Table(200) = &H95BF4A82
  m_CRC32Table(201) = &HE2B87A14
  m_CRC32Table(202) = &H7BB12BAE
  m_CRC32Table(203) = &HCB61B38
  m_CRC32Table(204) = &H92D28E9B
  m_CRC32Table(205) = &HE5D5BE0D
  m_CRC32Table(206) = &H7CDCEFB7
  m_CRC32Table(207) = &HBDBDF21
  m_CRC32Table(208) = &H86D3D2D4
  m_CRC32Table(209) = &HF1D4E242
  m_CRC32Table(210) = &H68DDB3F8
  m_CRC32Table(211) = &H1FDA836E
  m_CRC32Table(212) = &H81BE16CD
  m_CRC32Table(213) = &HF6B9265B
  m_CRC32Table(214) = &H6FB077E1
  m_CRC32Table(215) = &H18B74777
  m_CRC32Table(216) = &H88085AE6
  m_CRC32Table(217) = &HFF0F6A70
  m_CRC32Table(218) = &H66063BCA
  m_CRC32Table(219) = &H11010B5C
  m_CRC32Table(220) = &H8F659EFF
  m_CRC32Table(221) = &HF862AE69
  m_CRC32Table(222) = &H616BFFD3
  m_CRC32Table(223) = &H166CCF45
  m_CRC32Table(224) = &HA00AE278
  m_CRC32Table(225) = &HD70DD2EE
  m_CRC32Table(226) = &H4E048354
  m_CRC32Table(227) = &H3903B3C2
  m_CRC32Table(228) = &HA7672661
  m_CRC32Table(229) = &HD06016F7
  m_CRC32Table(230) = &H4969474D
  m_CRC32Table(231) = &H3E6E77DB
  m_CRC32Table(232) = &HAED16A4A
  m_CRC32Table(233) = &HD9D65ADC
  m_CRC32Table(234) = &H40DF0B66
  m_CRC32Table(235) = &H37D83BF0
  m_CRC32Table(236) = &HA9BCAE53
  m_CRC32Table(237) = &HDEBB9EC5
  m_CRC32Table(238) = &H47B2CF7F
  m_CRC32Table(239) = &H30B5FFE9
  m_CRC32Table(240) = &HBDBDF21C
  m_CRC32Table(241) = &HCABAC28A
  m_CRC32Table(242) = &H53B39330
  m_CRC32Table(243) = &H24B4A3A6
  m_CRC32Table(244) = &HBAD03605
  m_CRC32Table(245) = &HCDD70693
  m_CRC32Table(246) = &H54DE5729
  m_CRC32Table(247) = &H23D967BF
  m_CRC32Table(248) = &HB3667A2E
  m_CRC32Table(249) = &HC4614AB8
  m_CRC32Table(250) = &H5D681B02
  m_CRC32Table(251) = &H2A6F2B94
  m_CRC32Table(252) = &HB40BBE37
  m_CRC32Table(253) = &HC30C8EA1
  m_CRC32Table(254) = &H5A05DF1B
  m_CRC32Table(255) = &H2D02EF8D

  'Create a bytearray to hold the
  'precompiled assembler code
  sASM = "5589E557565053518B45088B008B750C8B7D108B4D1431DB8A1E30C3C1E80833049F464975F28B4D088901595B585E5F89EC5DC21000"
  ReDim m_CRC32Asm(0 To Len(sASM) \ 2 - 1)
  For i = 1 To Len(sASM) Step 2
    m_CRC32Asm(i \ 2) = Val("&H" & Mid$(sASM, i, 2))
  Next
  
  'Mark the CRC32 algorithm as initialized
  'm_CRC32Init = True
End Sub
