CalcCRC32 for 64-bit programs? - delphi

Question

I found this code in an older program from Angus Johnson:
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);
//CRC algorithm courtesy of Earl F. Glynn ...
//(http://www.efg2.com/Lab/Mathematics/CRC.htm)
function CalcCRC32(p: pchar; length: integer): dword;
var
i: integer;
begin
result := $FFFFFFFF;
for i := 0 to length-1 do
begin
result := (result shr 8) xor table[ pbyte(p)^ xor (result and $000000ff) ];
inc(p);
end;
result := not result;
end;
The CalcCRC32 function gives back erroneous results if the code is compiled in 64-bit program.
How could this function be changed to make it work in a 64-bit program in Delphi 10.1 Berlin?
The code has been taken from: TextDiff\BasicDemo2\HashUnit.pas on http://www.angusj.com/delphi/textdiff.html
I have used these two texts to test TextDiff:
Text 1:
CompanyName=Igor Pavlov
FileDescription=7-Zip Standalone Console
FileVersion=17.01 beta
InternalName=7za
LegalCopyright=Copyright (c) 1999-2017 Igor Pavlov
OriginalFilename=7za.exe
ProductName=7-Zip
ProductVersion=17.01 beta
Text2:
CompanyName=Igor Pavlov
FileDescription=7-Zip Standalone Console
FileVersion=4.61 beta
InternalName=7za
LegalCopyright=Copyright (c) 1999-2008 Igor Pavlov
OriginalFilename=7za.exe
ProductName=7-Zip
ProductVersion=4.61 beta
Here is how I changed the code according to the solution:
function CalcCRC32(p: PByte; length: NativeUInt): dword;
var
i: integer;
begin
result := $FFFFFFFF;
for i := 0 to length-1 do
begin
result := (result shr 8) xor table[ pbyte(p)^ xor (result and $000000ff) ];
inc(p);
end;
result := not result;
end;
function HashLine(const line: string; IgnoreCase, IgnoreBlanks: boolean): pointer;
var
i, j, len: integer;
s: String;
begin
s := line;
if IgnoreBlanks then
begin
i := 1;
j := 1;
len := length(line);
while i <= len do
begin
if not (line[i] in [#9,#32]) then
begin
s[j] := line[i];
inc(j);
end;
inc(i);
end;
setlength(s,j-1);
end;
if IgnoreCase then s := AnsiLowerCase(s);
//return result as a pointer to save typecasting later...
result := pointer(CalcCRC32(PByte(s), length(s)));
end;

Answer 1

In general, this code should work in 64bit, provided length does not exceed 2GB. That is not your issue.
The p parameter needs to be changed from PChar to PByte (or even just Pointer) since PChar is PWideChar in D2009+ but the code is expecting PChar to be PAnsiChar instead.
Also, you should probably change length from Integer to Native(U)Int so you can take better advantage of 64bit memory sizes greater than 2GB.
Now, with that said, if you want to get the CRC of a string, be aware that string is a UTF-16 encoded UnicodeString in D2009+, but CRC operates on bytes rather than characters. So, when computing the CRC of a string, you have to decide which byte encoding it should be converted to first. And when comparing the CRCs of multiple strings, make sure they are converted to the same byte encoding first.

Answer 2

You may read the following to better understand how string works in Delphi.
Here you have the interface section of an unicode aware HashLine function; there is no reason to use Pointer as the result type.
uses System.Types;
function HashLine(const line: string; IgnoreCase, IgnoreBlanks: boolean): dword;
Here the implementation part.
uses
System.SysUtils, System.StrUtils, System.Character, System.Classes;
const
table: ARRAY[0..255] OF DWORD =
($00000000, $77073096, $EE0E612C, $990951BA,
...
$B40BBE37, $C30C8EA1, $5A05DF1B, $2D02EF8D);
function CalcCRC32(p: PByte; length: NativeUInt): DWORD;
var
i: NativeUInt;
begin
result := $FFFFFFFF;
for i := 0 to length-1 do
begin
result := (result shr 8) xor table[ p^ xor (result and $000000ff) ];
inc(p);
end;
result := not result;
end;
function HashLine(const line: string; IgnoreCase, IgnoreBlanks: boolean): DWORD;
var
i, j: integer;
s: string;
b: TBytes;
begin
if IgnoreBlanks then
begin
j := low(string);
setlength(s, length(line));
for i := low(line) to high(line) do
begin
// if not (line[i] in [#9,#32]) then
if not line[i].IsWhiteSpace() then
begin
s[j] := line[i];
inc(j);
end;
end;
setlength(s,j-1);
end else begin
s := line;
end;
if IgnoreCase then
s := s.ToLower();
b := TEncoding.UTF8.GetBytes(s);
result := CalcCRC32(#b[0], length(b));
end;
The call HashLine('HEllo, World!', false, false) results F47B1828 which is equal to the result here

Answer 3

Just change result := not result; to result := result xor $FFFFFFFF;.