UNIT crc32;

{$I MKB.Def}


INTERFACE
{ Use a type Integer variable to store the crc value.                     }
{ Initialise the variable to $FFFFFFFF before running the crc routine.    }
{ VERY IMPORTANT!!!! -> This routine was developed for data communications}
{ and returns the crc bytes in LOW to HIGH order, NOT byte reversed!      }
{ To turn the valu into a 'normal' Integer, you must reverse the bytes!   }
{ e.g.                                                                    }
{ VAR                                                                     }
{    l, crc: Integer;                                                     }
{    list: ARRAY[0..1023] OF BYTE;                                        }
{    counter: SmallInt;                                                    }
{                                                                         }
{ BEGIN                                                                   }
{    crc := $FFFFFFFF;                           (* initialise  *)        }
{    FillChar(list,SizeOf(list),1);              (* dummy array *)        }
{    FOR counter := 0 TO (Pred(SizeOf(list))) DO (* run thru    *)        }
{       crc := UpdC32(buf[counter],crc);         (* finding crc *)        }
{    FOR counter := 1 TO 4 DO                    (* reverse     *)        }
{       l := (l SHL 8) OR BYTE(crc);             (* the bytes   *)        }
{    (* l now contains the 'normalized' crc *)                            }
{                                                                         }

FUNCTION UpdC32(octet: BYTE; crc: Integer) : Integer;

IMPLEMENTATION
(* Converted to Turbo Pascal (tm) V4.0 March, 1988 by J.R.Louvau       *)
(* Copyright (C) 1986 Gary S. Brown.  You may use this program, or     *)
(* code or tables extracted from it, as desired without restriction.   *)
(*                                                                     *)
(* First, the polynomial itself and its table of feedback terms.  The  *)
(* polynomial is                                                       *)
(* X^32+X^26+X^23+X^22+X^16+X^12+X^11+X^10+X^8+X^7+X^5+X^4+X^2+X^1+X^0 *)
(* Note that we take it "backwards" and put the highest-order term in  *)
(* the lowest-order bit.  The X^32 term is "implied"; the LSB is the   *)
(* X^31 term, etc.  The X^0 term (usually shown as "+1") results in    *)
(* the MSB being 1.                                                    *)
(*                                                                     *)
(* Note that the usual hardware shift register implementation, which   *)
(* is what we're using (we're merely optimizing it by doing eight-bit  *)
(* chunks at a time) shifts bits into the lowest-order term.  In our   *)
(* implementation, that means shifting towards the right.  Why do we   *)
(* do it this way?  Because the calculated CRC must be transmitted in  *)
(* order from highest-order term to lowest-order term.  UARTs transmit *)
(* characters in order from LSB to MSB.  By storing the CRC this way,  *)
(* we hand it to the UART in the order low-byte to high-byte; the UART *)
(* sends each low-bit to hight-bit; and the result is transmission bit *)
(* by bit from highest- to lowest-order term without requiring any bit *)
(* shuffling on our part.  Reception works similarly.                  *)
(*                                                                     *)
(* The feedback terms table consists of 256, 32-bit entries.  Notes:   *)
(*                                                                     *)
(*     The table can be generated at runtime if desired; code to do so *)
(*     is shown later.  It might not be obvious, but the feedback      *)
(*     terms simply represent the results of eight shift/xor opera-    *)
(*     tions for all combinations of data and CRC register values.     *)
(*                                                                     *)
(*     The values must be right-shifted by eight bits by the "updcrc"  *)
(*     logic; the shift must be unsigned (bring in zeroes).  On some   *)
(*     hardware you could probably optimize the shift in assembler by  *)
(*     using byte-swap instructions.                                   *)
(*     polynomial $edb88320                                            *)
(*                                                                     *)



CONST crc_32_tab: ARRAY[0..255] OF Integer = (
$00000000, $77073096, $ee0e612c, $990951ba, $076dc419, $706af48f, $e963a535, $9e6495a3,
$0edb8832, $79dcb8a4, $e0d5e91e, $97d2d988, $09b64c2b, $7eb17cbd, $e7b82d07, $90bf1d91,
$1db71064, $6ab020f2, $f3b97148, $84be41de, $1adad47d, $6ddde4eb, $f4d4b551, $83d385c7,
$136c9856, $646ba8c0, $fd62f97a, $8a65c9ec, $14015c4f, $63066cd9, $fa0f3d63, $8d080df5,
$3b6e20c8, $4c69105e, $d56041e4, $a2677172, $3c03e4d1, $4b04d447, $d20d85fd, $a50ab56b,
$35b5a8fa, $42b2986c, $dbbbc9d6, $acbcf940, $32d86ce3, $45df5c75, $dcd60dcf, $abd13d59,
$26d930ac, $51de003a, $c8d75180, $bfd06116, $21b4f4b5, $56b3c423, $cfba9599, $b8bda50f,
$2802b89e, $5f058808, $c60cd9b2, $b10be924, $2f6f7c87, $58684c11, $c1611dab, $b6662d3d,
$76dc4190, $01db7106, $98d220bc, $efd5102a, $71b18589, $06b6b51f, $9fbfe4a5, $e8b8d433,
$7807c9a2, $0f00f934, $9609a88e, $e10e9818, $7f6a0dbb, $086d3d2d, $91646c97, $e6635c01,
$6b6b51f4, $1c6c6162, $856530d8, $f262004e, $6c0695ed, $1b01a57b, $8208f4c1, $f50fc457,
$65b0d9c6, $12b7e950, $8bbeb8ea, $fcb9887c, $62dd1ddf, $15da2d49, $8cd37cf3, $fbd44c65,
$4db26158, $3ab551ce, $a3bc0074, $d4bb30e2, $4adfa541, $3dd895d7, $a4d1c46d, $d3d6f4fb,
$4369e96a, $346ed9fc, $ad678846, $da60b8d0, $44042d73, $33031de5, $aa0a4c5f, $dd0d7cc9,
$5005713c, $270241aa, $be0b1010, $c90c2086, $5768b525, $206f85b3, $b966d409, $ce61e49f,
$5edef90e, $29d9c998, $b0d09822, $c7d7a8b4, $59b33d17, $2eb40d81, $b7bd5c3b, $c0ba6cad,
$edb88320, $9abfb3b6, $03b6e20c, $74b1d29a, $ead54739, $9dd277af, $04db2615, $73dc1683,
$e3630b12, $94643b84, $0d6d6a3e, $7a6a5aa8, $e40ecf0b, $9309ff9d, $0a00ae27, $7d079eb1,
$f00f9344, $8708a3d2, $1e01f268, $6906c2fe, $f762575d, $806567cb, $196c3671, $6e6b06e7,
$fed41b76, $89d32be0, $10da7a5a, $67dd4acc, $f9b9df6f, $8ebeeff9, $17b7be43, $60b08ed5,
$d6d6a3e8, $a1d1937e, $38d8c2c4, $4fdff252, $d1bb67f1, $a6bc5767, $3fb506dd, $48b2364b,
$d80d2bda, $af0a1b4c, $36034af6, $41047a60, $df60efc3, $a867df55, $316e8eef, $4669be79,
$cb61b38c, $bc66831a, $256fd2a0, $5268e236, $cc0c7795, $bb0b4703, $220216b9, $5505262f,
$c5ba3bbe, $b2bd0b28, $2bb45a92, $5cb36a04, $c2d7ffa7, $b5d0cf31, $2cd99e8b, $5bdeae1d,
$9b64c2b0, $ec63f226, $756aa39c, $026d930a, $9c0906a9, $eb0e363f, $72076785, $05005713,
$95bf4a82, $e2b87a14, $7bb12bae, $0cb61b38, $92d28e9b, $e5d5be0d, $7cdcefb7, $0bdbdf21,
$86d3d2d4, $f1d4e242, $68ddb3f8, $1fda836e, $81be16cd, $f6b9265b, $6fb077e1, $18b74777,
$88085ae6, $ff0f6a70, $66063bca, $11010b5c, $8f659eff, $f862ae69, $616bffd3, $166ccf45,
$a00ae278, $d70dd2ee, $4e048354, $3903b3c2, $a7672661, $d06016f7, $4969474d, $3e6e77db,
$aed16a4a, $d9d65adc, $40df0b66, $37d83bf0, $a9bcae53, $debb9ec5, $47b2cf7f, $30b5ffe9,
$bdbdf21c, $cabac28a, $53b39330, $24b4a3a6, $bad03605, $cdd70693, $54de5729, $23d967bf,
$b3667a2e, $c4614ab8, $5d681b02, $2a6f2b94, $b40bbe37, $c30c8ea1, $5a05df1b, $2d02ef8d
);

FUNCTION UpdC32(octet: BYTE; crc: Integer) : Integer;
BEGIN { UpdC32 }
   UpdC32 := crc_32_tab[BYTE(crc XOR Integer(octet))] XOR ((crc SHR 8) AND $00FFFFFF)
END;

END. {unit}
