5.1 32-Bit CRC Algorithm

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This section uses pseudo code to explain how to generate the 32-bit CRC value stored in the CRC field of the COMPRESSED_BLOCK_HEADER structure.

 Define CalculateCRC32 as Function With Parameters (
     buffer as unsigned char []
     length as unsigned integer
     )
 Begin
     Define crc as unsigned integer
     Define index as integer
  
     crc = 0xFFFFFFFF
     index := 0
     While (index < length) 
     Begin
         crc := crc32_table [(crc AND 0xFF) XOR buffer [index]] ^ (crc / 256)
         index := index + 1
     End
     return crc XOR 0xFFFFFFFF
 End
  
 Define crc32_table as unsigned integer [256] =
 Begin
     0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA,
     0x076DC419, 0x706AF48F, 0xE963A535, 0x9E6495A3,
     0x0EDB8832, 0x79DCB8A4, 0xE0D5E91E, 0x97D2D988,
     0x09B64C2B, 0x7EB17CBD, 0xE7B82D07, 0x90BF1D91,
     0x1DB71064, 0x6AB020F2, 0xF3B97148, 0x84BE41DE,
     0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7,
     0x136C9856, 0x646BA8C0, 0xFD62F97A, 0x8A65C9EC,
     0x14015C4F, 0x63066CD9, 0xFA0F3D63, 0x8D080DF5,
     0x3B6E20C8, 0x4C69105E, 0xD56041E4, 0xA2677172,
     0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B,
     0x35B5A8FA, 0x42B2986C, 0xDBBBC9D6, 0xACBCF940,
     0x32D86CE3, 0x45DF5C75, 0xDCD60DCF, 0xABD13D59,
     0x26D930AC, 0x51DE003A, 0xC8D75180, 0xBFD06116,
     0x21B4F4B5, 0x56B3C423, 0xCFBA9599, 0xB8BDA50F,
     0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924,
     0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D,
     0x76DC4190, 0x01DB7106, 0x98D220BC, 0xEFD5102A,
     0x71B18589, 0x06B6B51F, 0x9FBFE4A5, 0xE8B8D433,
     0x7807C9A2, 0x0F00F934, 0x9609A88E, 0xE10E9818,
     0x7F6A0DBB, 0x086D3D2D, 0x91646C97, 0xE6635C01,
     0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E,
     0x6C0695ED, 0x1B01A57B, 0x8208F4C1, 0xF50FC457,
     0x65B0D9C6, 0x12B7E950, 0x8BBEB8EA, 0xFCB9887C,
     0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3, 0xFBD44C65,
     0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2,
     0x4ADFA541, 0x3DD895D7, 0xA4D1C46D, 0xD3D6F4FB,
     0x4369E96A, 0x346ED9FC, 0xAD678846, 0xDA60B8D0,
     0x44042D73, 0x33031DE5, 0xAA0A4C5F, 0xDD0D7CC9,
     0x5005713C, 0x270241AA, 0xBE0B1010, 0xC90C2086,
     0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F,
     0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4,
     0x59B33D17, 0x2EB40D81, 0xB7BD5C3B, 0xC0BA6CAD,
     0xEDB88320, 0x9ABFB3B6, 0x03B6E20C, 0x74B1D29A,
     0xEAD54739, 0x9DD277AF, 0x04DB2615, 0x73DC1683,
     0xE3630B12, 0x94643B84, 0x0D6D6A3E, 0x7A6A5AA8,
     0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1,
     0xF00F9344, 0x8708A3D2, 0x1E01F268, 0x6906C2FE,
     0xF762575D, 0x806567CB, 0x196C3671, 0x6E6B06E7,
     0xFED41B76, 0x89D32BE0, 0x10DA7A5A, 0x67DD4ACC,
     0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5,
     0xD6D6A3E8, 0xA1D1937E, 0x38D8C2C4, 0x4FDFF252,
     0xD1BB67F1, 0xA6BC5767, 0x3FB506DD, 0x48B2364B,
     0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6, 0x41047A60,
     0xDF60EFC3, 0xA867DF55, 0x316E8EEF, 0x4669BE79,
     0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236,
     0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F,
     0xC5BA3BBE, 0xB2BD0B28, 0x2BB45A92, 0x5CB36A04,
     0xC2D7FFA7, 0xB5D0CF31, 0x2CD99E8B, 0x5BDEAE1D,
     0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A,
     0x9C0906A9, 0xEB0E363F, 0x72076785, 0x05005713,
     0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38,
     0x92D28E9B, 0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21,
     0x86D3D2D4, 0xF1D4E242, 0x68DDB3F8, 0x1FDA836E,
     0x81BE16CD, 0xF6B9265B, 0x6FB077E1, 0x18B74777,
     0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C,
     0x8F659EFF, 0xF862AE69, 0x616BFFD3, 0x166CCF45,
     0xA00AE278, 0xD70DD2EE, 0x4E048354, 0x3903B3C2,
     0xA7672661, 0xD06016F7, 0x4969474D, 0x3E6E77DB,
     0xAED16A4A, 0xD9D65ADC, 0x40DF0B66, 0x37D83BF0,
     0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9,
     0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6,
     0xBAD03605, 0xCDD70693, 0x54DE5729, 0x23D967BF,
     0xB3667A2E, 0xC4614AB8, 0x5D681B02, 0x2A6F2B94,
     0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D
 End
  
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