efg's Mathematics Projects -- CRC Calculator

Cyclic Redundancy Code Calculator

Lab Report

Calculate CRC of Character String using CRC Calculator (Also see the FileCheck Lab Report for CRCs of Files, Directories, Volumes) Delphi 7 CLX Version (Windows)

	Calculate CRC of File using CRC Calculator Kylix 3 CLX Version (Linux)

Purpose
The purpose of the CRCCalculator is to display interactively the CRC-16 and CRC-32 values for a specified string or file. (The CRC-32 values will match those computed by PKZIP.)

Additional files, CRC16Dem and CRC32Dem, show how to create a command-line program to calculate CRC values. A "C" command-line program is also available.

Materials and Equipment

Software Requirements
Windows 95/98/2000 and Delphi 3/4/5/6/7 (to recompile)
or
Linux and Kylix 3 (to recompile)

Hardware Requirements
VGA display

Procedure

Double click on the CRCCalculator.EXE icon to start the program (Windows), or run the program under Linux using ./CrcCalculator..
Enter any text in the edit box.
Observe the CRC-16 and CRC-32 values in decimal or hexadecimal.
Select File tabsheet.
Click on the Read button and select a file
Observe the CRC-16 and CRC-32 values in decimal or hexadecimal.

Expected Values
Hex values do not change by version of Delphi, but the decimal values are intended to be unsigned. CRC-16 values have always been unsigned, but since there was no 4-byte unsigned integer in D1-D3, the decimal values are signed for the CRC-32 until the Delphi 4 version.

Test String	CRC-16 Init Method 1		CRC-16 Init Method 2		CRC-32 Init Method 2		Comments
Test String	Decimal	Hex	Decimal	Hex	Decimal	Hex	Comments
<null string>	0	0000	0	0000	0	00000000	Delphi 2 - 7, Kylix 3
abc	38712	9738	43190	A8B6	891568578	352441C2	Delphi 2 - 7, Kylix 3
ABC	38712	4521	31407	7AAF	-1551695032	A3830348	Delphi 2 - 3
ABC	38712	4521	31407	7AAF	2743272264	A3830348	Delphi 4 - 7, Kylix 3
This is a string	19524	4C44	17157	4305	141976383	0876633F	Delphi 2 - 7, Kylix 3

See the Initialization/Finalization discussion below for a description of Initialization Methods 1 and 2.

See Felipe Rocha Machado's comments about printing 32-bit integers in D3.

The CRC-32s of the files abcLower.TXT, ABCupper.TXT, and ThisIsAString.TXT in the CRCDelphi.ZIP file match the values above, which are also verified in the CRC32Dem.PAS command line program:

CRC-32    Bytes         F i l e n a m e
-------- -------- ------------------------
352441C2        3 abcLower.TXT
A3830348        3 ABCUpper.TXT
0876633F       16 ThisIsAString.TXT

Discussion
CRC values, especially the CRC-32, are an extremely good way to verify the integrity of a file. If the CRC-32 for a file stays the same, there is only an extremely small probability that the file has been changed -- about 1 in 4 billion. CRCs could be used as a preliminary verification tool to find identical files. If the CRCs of two files do not match, the file are not the same. This could even be used to compare image files.

Lookup Tables. The "hardware" method of computing CRCs involves bit manipulations, which is very inefficient for a software computation. Instead of computing the CRC bit-by-bit, a 256-element lookup table can be used to perform the equivalent of 8 bit operations at a time. (This is described in "Byte-wise CRC Calculations" in IEEE Micro, June 1983, pp. 40-50.)

For a CRC-16, the lookup table consists of 256 2-byte WORDs (see below, or the CRC16.PAS unit for the actual table, or the CRCTable program for computation of the lookup table for the x¹⁶ + x¹⁵ + x² + 1 generator polynomial):

CONST
table: ARRAY[0..255] OF WORD =
($0000,$C0C1,$C181,$0140,$C301,$03C0,$0280,$C241,$C601,$06C0,$0780,
$C741,$0500,$C5C1,$C481,$0440,$CC01,$0CC0,$0D80,$CD41,$0F00,$CFC1,
$CE81,$0E40,$0A00,$CAC1,$CB81,$0B40,$C901,$09C0,$0880,$C841,$D801,
$18C0,$1980,$D941,$1B00,$DBC1,$DA81,$1A40,$1E00,$DEC1,$DF81,$1F40,
$DD01,$1DC0,$1C80,$DC41,$1400,$D4C1,$D581,$1540,$D701,$17C0,$1680,
$D641,$D201,$12C0,$1380,$D341,$1100,$D1C1,$D081,$1040,$F001,$30C0,
$3180,$F141,$3300,$F3C1,$F281,$3240,$3600,$F6C1,$F781,$3740,$F501,
$35C0,$3480,$F441,$3C00,$FCC1,$FD81,$3D40,$FF01,$3FC0,$3E80,$FE41,
$FA01,$3AC0,$3B80,$FB41,$3900,$F9C1,$F881,$3840,$2800,$E8C1,$E981,
$2940,$EB01,$2BC0,$2A80,$EA41,$EE01,$2EC0,$2F80,$EF41,$2D00,$EDC1,
$EC81,$2C40,$E401,$24C0,$2580,$E541,$2700,$E7C1,$E681,$2640,$2200,
$E2C1,$E381,$2340,$E101,$21C0,$2080,$E041,$A001,$60C0,$6180,$A141,
$6300,$A3C1,$A281,$6240,$6600,$A6C1,$A781,$6740,$A501,$65C0,$6480,
$A441,$6C00,$ACC1,$AD81,$6D40,$AF01,$6FC0,$6E80,$AE41,$AA01,$6AC0,
$6B80,$AB41,$6900,$A9C1,$A881,$6840,$7800,$B8C1,$B981,$7940,$BB01,
$7BC0,$7A80,$BA41,$BE01,$7EC0,$7F80,$BF41,$7D00,$BDC1,$BC81,$7C40,
$B401,$74C0,$7580,$B541,$7700,$B7C1,$B681,$7640,$7200,$B2C1,$B381,
$7340,$B101,$71C0,$7080,$B041,$5000,$90C1,$9181,$5140,$9301,$53C0,
$5280,$9241,$9601,$56C0,$5780,$9741,$5500,$95C1,$9481,$5440,$9C01,
$5CC0,$5D80,$9D41,$5F00,$9FC1,$9E81,$5E40,$5A00,$9AC1,$9B81,$5B40,
$9901,$59C0,$5880,$9841,$8801,$48C0,$4980,$8941,$4B00,$8BC1,$8A81,
$4A40,$4E00,$8EC1,$8F81,$4F40,$8D01,$4DC0,$4C80,$8C41,$4400,$84C1,
$8581,$4540,$8701,$47C0,$4680,$8641,$8201,$42C0,$4380,$8341,$4100,
$81C1,$8081,$4040);

Given the above lookup table, the code for computing a CRC-16 is as follows (see initialization/finalization below):

PROCEDURE CalcCRC16 (p: pByte; nbyte: WORD; VAR CRCvalue: WORD);
VAR
    i: WORD;
    q: pByte;

{The following is a little cryptic (but executes very quickly).
   The algorithm is as follows:
   1. exclusive-or the input byte with the low-order byte of
      the CRC register to get an INDEX
   2. shift the CRC register eight bits to the right
   3. exclusive-or the CRC register with the contents of
      Table[INDEX]
   4. repeat steps 1 through 3 for all bytes}
BEGIN
q := p;
FOR i := 1 TO nBYTE DO
BEGIN
    CRCvalue := Hi(CRCvalue) XOR Table[ q^ XOR Lo(CRCvalue) ];
    INC(q)
END
END {CalcCRC16};

For a CRC-32, the lookup table consists of 256 4-byte DWORDs (also see the CRC32.PAS unit).

// The constants here are for the CRC-32 generator
// polynomial, as defined in the Microsoft
// Systems Journal, March 1995, pp. 107-108

CONST
table: ARRAY[0..255] OF DWORD =
($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);

Given the above lookup table, the code for computing a CRC-32 is as follows (see initialization/finalization below):

// Use CalcCRC32 as a procedure so CRCValue can be passed in but
// also returned. This allows multiple calls to CalcCRC32 for
// the "same" CRC-32 calculation.
PROCEDURE CalcCRC32 (p: pointer; ByteCount: DWORD; VAR CRCValue: DWORD);
// The following is a little cryptic (but executes very quickly).
// The algorithm is as follows:
// 1. exclusive-or the input byte with the low-order byte of
// the CRC register to get an INDEX
// 2. shift the CRC register eight bits to the right
// 3. exclusive-or the CRC register with the contents of Table[INDEX]
// 4. repeat steps 1 through 3 for all bytes

VAR
    i: DWORD;
    q: ^BYTE;
BEGIN
q := p;
FOR i := 0 TO ByteCount-1 DO
BEGIN
    CRCvalue := (CRCvalue SHR 8) XOR
    Table[ q^ XOR (CRCvalue AND $000000FF) ];
    INC(q)
END
END {CalcCRC32};

You can pass nearly any argument to this routine since the first parameter is a pointer. For a string, pass the address of the first character, for example:

CalcCRC32 (Addr(s[1]), LENGTH(s), CRC32);

To avoid an access violation in Delphi 4 (or later) make sure Length(s) > 0. (I'm not sure why Delphi 3 didn't complain.)

This routine can be used to verify the CRC32 table of constants has not been accidentally modified. The following code in the CRC32 unit initialization checks the 1024-byte array of DWORDs:

VAR
CRC32Table: DWORD;

BEGIN
// Verify the table used to compute the CRCs has not been modified.
// Thanks to Gary Williams for this suggestion, Jan. 2003.
CRC32Table := $FFFFFFFF;
CalcCRC32 (Addr(table[0]), SizeOf(table), CRC32Table);
CRC32Table := NOT CRC32Table;

IF CRC32Table <> $6FCF9E13
THEN ShowMessage('CRC32 Table CRC32 is ' +
IntToHex(Crc32Table, 8) +
', expecting $6FCF9E13');
END {CRC32}.

To compute the same CRC-32 as used in the PKZIP utility, start with a CRCvalue of $FFFFFFFF. After calling CalcCRC32 above (any number of times), the finalization consists of a 1's complement of the CRCvalue. This can be computed with the expression NOT CRCvalue in Delphi. See additional details in the next section.

Initialization and Finalization. The initialization and finalization of the CRC computation are arbitrary. Many years ago when I first started computing CRCs, I set the initial value to 0 and did no finalization -- this is "Method 1" described above under Expected Values.

CRC16 := 0;
IF LENGTH(s) > 0 // Avoid access violation in D4
THEN CalcCRC16 (Addr(s[1]), LENGTH(s), CRC16);

The "standard" CRC-32 (the one used by PKZIP) starts with $FFFFFFFF as the initial value and then performs a 1's complement to yield the final value -- this is "Method 2" described above under Expected Values. Here's what is done in the CRC Calculator for CRC-32s:

CRC32 := $FFFFFFFF; // To match PKZIP
IF LENGTH(s) > 0 // Avoid access violation in D4
THEN CalcCRC32 (Addr(s[1]), LENGTH(s), CRC32);
CRC32 := NOT CRC32; // TO match PKZIP

In the CRC16 computation the initial value is $FFFF with Method 2.

[Thanks to Rolf Gebhardt and Glen Harman for pointing out an inconsistency about how finalization was handled in an earlier version of this article.]

CRC of a File. All the bytes of a file must be passed to the CalcCRC routines, i.e., CalcCRC16 and CalcCRC32, to compute the CRC of a file. The older BlockRead I/O primitive is used in the CalcFileCRC16 routine in the CRC16 unit since BlockRead at one point was the only way to read a binary stream of bytes. CalcFileCRC32 uses the more contemporary memory stream to read the bytes of a file (when the StreamIO conditional compilation is defined).

// Use MemoryStream to read file in binary mode.
PROCEDURE CalcFileCRC32 (FromName: STRING; VAR CRCvalue: DWORD;
    VAR TotalBytes: TInteger8;
    VAR error: WORD);
VAR
    Stream: TMemoryStream;
BEGIN
error := 0;
CRCValue := $FFFFFFFF;
Stream := TMemoryStream.Create;
TRY
    TRY
      Stream.LoadFromFile(FromName);
      IF   Stream.Size > 0
      THEN CalcCRC32 (Stream.Memory, Stream.Size, CRCvalue)
    EXCEPT
      ON E: EReadError DO
      error := 1
    END;

    CRCvalue := NOT CRCvalue;
    TotalBytes := Stream.Size
FINALLY
    Stream.Free
END;
END {CalcFileCRC32};

The above procedure assumes that the file will easily fit into memory in a TMemoryStream. Unfortunately, this can be a bad assumption especially when some files are bigger than physical memory. For example, processing a 1 GB file in a memory stream with only 512 MB of physical memory might at minimum will tax the virtual memory processing of the operating system. For now, this isn't much of a problem.

See Ted T�raasen's modification for CRC-16s for buffers > 64 KB.

FileCheck Program. See the FileCheck Lab Report for information about creating CRCs of files, directories, or even whole volumes. ("Meta" CRCs -- that is, CRCs of CRCs of a well-ordered list of files -- used to detect changes in directories or whole disk volumes.)

Command Line Programs. The command line examples, CRC16Dem and CRC32Dem can be compiled from a DOS Window (assuming your path contains the Delphi bin directory) by entering:

DCC32 CRC16Dem.PAS or
DCC32 CRC32Dem.PAS

Study the CRC16Dem and CRC32Dem command line programs for a way to calculate CRCs without a Windows interface.

The Delphi installation CD has a file CRC32.C, which shows how to compute CRC-32s, as well as the lookup table, in the directory \Info\Extras\Zlib\Src.

CRC Links

A Painless Guide to CRC Error Detection Algorithms
www.ross.net/crc/crcpaper.html
www.microconsultants.com/tips/crc/crc.txt
www.geocities.com/SiliconValley/Pines/8659/crc.htm

Peter Haas' Delphi unit for demonstration calculation of CRC, based on the document: "A Painless Guide to CRC Error Detection Algorithms"
ftp://ftp.rocksoft.com/papers/crc_v3.txt

Peter Haas' unit contains functions to calculate a arbitrary CRC (up to 32 bit) by given parameters (Polynom, Init, XorOut, ReflectIn, ReflectOut). A
another part is the generation of a Lookup Table and the calculation with this table. The unit can also used to find the parameters for a unknown CRC calculation with trial and error. Last but not least, it contain the unit a function, that creates Delphi source to calculate a CRC with the given parameters in a separate application.
http://delphi.pjh2.de/units/download/CRCs.zip

Find code for CRC-16 CCITT here:
http://home.t-online.de/home/uwe.mnich/Wissen/Delphi/Utilities/Utilities.html

Cyclic Redundancy Check Computation (Texas Instruments Application Report)
- Coding theory behind CRC
- Algorithms for CRC computation
www.ti.com/sc/docs/psheets/abstract/apps/spra530.htm
http://www-s.ti.com/sc/psheets/spra530/spra530.pdf

"For the Love of the Game" by Michael Barr, Embedded Systems Programming, Dec. 1999, pp. 47-54.
www.embedded.com/internet/9912/9912connect.htm

"Slow and Steady Never Lost the Race" by Michael Barr, Embedded Systems Programming, Jan. 2000, pp. 37-46. Shows how to compute CRC lookup table. www.embedded.com/internet/0001/0001connect.htm

The CRC Pitstop is a repository for information on CRC and other checking algorithms
www.ross.net/crc

CRC and How to Reverse it
www.yates2k.net/anarchriz_crc.htm
www.woodmann.com/fravia/crctut1.htm
http://pilorama.com.ru/library/pdf/crcrevrs.pdf (in Russian)

CRC - Der Cyclic Redundancy Code (in German)
www.informatik.uni-frankfurt.de/~haase/crc.html

Understanding Cyclic Redundancy Check
www.4d.com/ACIDOC/CMU/CMU79909.HTM

Robert Lee's optimized code for CRC computation:
www.optimalcode.com/excrc.zip

Checksum-Algorithms: XOR16, XOR32, CRC32
http://delphi.icm.edu.pl/ftp/d20free/cipher.zip

Steve Schafer's UseNet Post showing calculation of CRC-32 Lookup Table

Bj�rn Kriedemann's UseNet Post with CRC Unit from April 1997 DDJ: CRC16, XYZModemCRC16, CRC32

Lars Truijens's UseNet Post showing Delphi code for XModem CRC-16 (X¹⁶ + X¹² + X⁵ + 1) with a Lookup Table

CRC-16 (X¹⁶+X¹⁵+X²+1) without lookup table, www.ibrtses.com/delphi/dcrc.html .

CRC-16 Calculator in Visual Basic by Stuart Rolfe

A CRC Calculator Unit provides three speed-optimized functions to compute (or continue computation of) a Cyclic Redundancy Check (CRC). Applicable to XModem protocol (16-bit CRC), SEA's "ARC" utility, PKZip (32-bit CRC) and many others compatible software, http://delphi.icm.edu.pl/ftp/d10free/crc.zip .

SWAG (Software Archive Group) CRC Snipets: Includes various CRC and Checksum routines
www.gdsoft.com/swag/downloads.html
www.gdsoft.com/swag/crc.zip (requires "Reader" program to view)

Algorithm of CRC-32 calculation for file
www.scalabium.com/faq/dct0048.htm

"Calculating CRC Checksums in C++" by Colin Mahoney in June 1999 C/C++ Users Journal.

Algorithms Alfresco: Whirlpool (CRC Algorithms), Julian Bucknall unravels CRC, Delphi Magazine, Issue 48, August 1999.

Split and Join (use CRCs to verify copy is correct after a file is split into separate floppy-size files and later rejoined)
www.undu.com/Articles/010511d.html

CRC-32 used in PNG graphics file format
http://www.libpng.org/pub/png/spec/PNG-Structure.html#CRC-algorithm

The D7 "Companion Tools" (Disk 1) has a directory \nag_software_solutions\crc32_library with a CRC32.EXE file from NAG Software Solutions.

Implementing CRCCs in Altera Devices
www.altera.com/literature/an/an049.pdf

See the CRC32 Library on CD #1 of the Delphi Studio Companion Tools.

Check Digits (credit cards and the "Modulo 10" check digit algorithm)
www.delphiforfun.org/Programs/Check_digits.htm

Related
MD5 Homepage (unofficial)

Useful literature:
"Procedure for Computing CRC-32 Values," Microsoft Systems Journal, March 1995, pp. 107-108.

"Byte-wise CRC Calculations" by Aram Perez in IEEE Micro, June 1983, pp. 40-50. Shows how to create a lookup table which is the best way to implement in software (versus the shifts that are done when implemented in hardware).

"A Tutorial on CRC Computations" by Tenkasi V. Ramabadran and Sunil S. Gaitonde in IEEE Micro, August 1988, pp. 62-75.

"Cyclic Redundancy Checks for Data Integrity or Identity" by William H. Press and Saul A. Teukolsky, Computers in Physics, Jul/Aug 1989, pp. 88-91.

Standard Name	SDLC (CCITT) (X25)	CRC-16	CRC-32 (Ethernet)
Width	16 bits	16 bits	32 bits
Generator Polynomial	10001000000100001 x¹⁶+ x¹² + x⁵ + 1	11000000000000101 x¹⁶ + x¹⁵ + x² + 1	100000100110000010001110110110111 x³² + x²⁶ + x²³ + x²² + x¹⁶ + x¹² + x¹¹ + x¹⁰ + x⁸ + x⁷ + x⁵ + x⁴ + x² + x¹ + 1
Initial remainder	0xFFFF	0x0000	0xFFFFFFFF
Final XOR value	0x0000	0x0000	0xFFFFFFFF

Other standard polynomials:
CRC-16 Reverse: x¹⁶ + x¹⁴ + x¹ + 1
SDLC Reverse: x¹⁶ + x¹¹ + x⁴ + 1
CRC-12: x¹² + x¹¹ + x³ + x² + x¹ + 1

Conclusions
CRC values, especially the CRC-32, are an extremely good way to verify the integrity of a string or even a file.

Keywords
cyclic redundancy check, CRC-16, CRC-32, APPTYPE CONSOLE, lookup table, XOR, Comp, Int64, IntToHex, Addr, Delphi, Kylix

Files

CLX (Component Library for Cross-Platform -- Windows or Linux)

Delphi 7 Source and CRCCalculator.EXE: CRCCLX.zip

Kylix 3 Source and CrcCalculator executable: CRCCLX.tar.gz
In Linux to extract files: gunzip < CRCCLX.tar.gz | tar xvf -

VCL (Visual Component Library -- Windows only)

Delphi 2 - 6 Source and EXE (234 KB): CRCDelphi.ZIP (old version)

Borland C++ 5.02 "C" CRC-32 Source and EXE (45 KB): CRCc.ZIP
Use the "make file" to compile: make -f crc32.mak
Modify .mak file to point to correct location of wildargs.obj. The .mak file automatically performs a test that the results will match those of PKZIP.) This command-line utility can be used with wildcards to find the CRC-32 of files in a directory, for example: crc32 *.*

TuboPascal 5.5 program to compute values for CRC-16 lookup table.

Updated	14 Jun 2009
Since	29 Nov 1998