How is a CRC32 checksum calculated with FreePascal(Lazarus)?
1
I have to make some project for my college, and I need to calculate CRC32. But I almost didn't work with shifts before, so even after I read theory it's still hard to me. I found some CRC32 basic algorithm for C (not mine) and I tried to rewrite it for Lazarus(Delphi). But it doesn't work. I can't understand, what's wrong. Please, help (*_ _)人
Here my code:
procedure TMyFrame.CRC32_Checksum();
var
P : Pointer;
Size, i : Integer;
CRC, j : LongWord;
B : ^Byte;
flag : Boolean;
begin
AssignFile (f, FileName);
Reset(f, 1);
Size := FileSize(f);
GetMem(P, Size);
BlockRead(f, P^, Size);
B := P;
//
//
CRC := $FFFFFFFF;
for i := 1 to Size do
begin
CRC := CRC XOR B^;
Inc(B);
for j := 0 to 7 do
begin
flag := (CRC AND 1) > 0;
if flag then
CRC := (CRC SHR 1) XOR $04C11DB7
else
CRC := CRC SHR 1;
end;
end;
LabeledEdit1.Text := IntToHEX(CRC, 8);
//
//
Freemem(P);
CloseFile(f);
end;
lazarus crc32
asked Nov 14 '18 at 14:32
ClaireClaire
112
|
show 2 more comments
1
I have to make some project for my college, and I need to calculate CRC32. But I almost didn't work with shifts before, so even after I read theory it's still hard to me. I found some CRC32 basic algorithm for C (not mine) and I tried to rewrite it for Lazarus(Delphi). But it doesn't work. I can't understand, what's wrong. Please, help (*_ _)人
Here my code:
procedure TMyFrame.CRC32_Checksum();
var
P : Pointer;
Size, i : Integer;
CRC, j : LongWord;
B : ^Byte;
flag : Boolean;
begin
AssignFile (f, FileName);
Reset(f, 1);
Size := FileSize(f);
GetMem(P, Size);
BlockRead(f, P^, Size);
B := P;
//
//
CRC := $FFFFFFFF;
for i := 1 to Size do
begin
CRC := CRC XOR B^;
Inc(B);
for j := 0 to 7 do
begin
flag := (CRC AND 1) > 0;
if flag then
CRC := (CRC SHR 1) XOR $04C11DB7
else
CRC := CRC SHR 1;
end;
end;
LabeledEdit1.Text := IntToHEX(CRC, 8);
//
//
Freemem(P);
CloseFile(f);
end;
lazarus crc32
asked Nov 14 '18 at 14:32
ClaireClaire
112
We don't know what it is meant to do, and how it fails. You need to learn how to debug your program. That's your next task.
– David Heffernan
Nov 14 '18 at 14:47
my program just looking for checksum and finds wrong numbers. It checks .txt file where "123456789" and it finds "0x340BC6D9", but it must be "0xCBF43926". I already tried to debug as you said, but I have no idea what's problem here. That's why I asking here about my problem
– Claire
Nov 14 '18 at 15:17
There are many variants of CRC32 algorithm. Who knows which one you want? Presumably you do. You have working C code, and now want Pascal code. Compare the execution of the two versions (Pascal against C). Find out where the two diverge. Fix, and repeat. When there is no more divergence, the task is done. Once again, your next task it to learn how to debug. This is the perfect opportunity. Would you like to learn how to debug? Or do you just want code that works?
– David Heffernan
Nov 14 '18 at 15:20
I'd like to learn how to debug, I guess... okay then, I'll try once again
– Claire
Nov 14 '18 at 15:29
Just do what I say. Compare the execution of the two programs, the C version and the Pascal version. Output (e.g. to console) the value ofCRCeach time around the loop and compare the outputs of those two programs. Take it from there.
– David Heffernan
Nov 14 '18 at 15:32
|
show 2 more comments
1
1
1
1
I have to make some project for my college, and I need to calculate CRC32. But I almost didn't work with shifts before, so even after I read theory it's still hard to me. I found some CRC32 basic algorithm for C (not mine) and I tried to rewrite it for Lazarus(Delphi). But it doesn't work. I can't understand, what's wrong. Please, help (*_ _)人
Here my code:
procedure TMyFrame.CRC32_Checksum();
var
P : Pointer;
Size, i : Integer;
CRC, j : LongWord;
B : ^Byte;
flag : Boolean;
begin
AssignFile (f, FileName);
Reset(f, 1);
Size := FileSize(f);
GetMem(P, Size);
BlockRead(f, P^, Size);
B := P;
//
//
CRC := $FFFFFFFF;
for i := 1 to Size do
begin
CRC := CRC XOR B^;
Inc(B);
for j := 0 to 7 do
begin
flag := (CRC AND 1) > 0;
if flag then
CRC := (CRC SHR 1) XOR $04C11DB7
else
CRC := CRC SHR 1;
end;
end;
LabeledEdit1.Text := IntToHEX(CRC, 8);
//
//
Freemem(P);
CloseFile(f);
end;
lazarus crc32
asked Nov 14 '18 at 14:32
ClaireClaire
112
I have to make some project for my college, and I need to calculate CRC32. But I almost didn't work with shifts before, so even after I read theory it's still hard to me. I found some CRC32 basic algorithm for C (not mine) and I tried to rewrite it for Lazarus(Delphi). But it doesn't work. I can't understand, what's wrong. Please, help (*_ _)人
Here my code:
procedure TMyFrame.CRC32_Checksum();
var
P : Pointer;
Size, i : Integer;
CRC, j : LongWord;
B : ^Byte;
flag : Boolean;
begin
AssignFile (f, FileName);
Reset(f, 1);
Size := FileSize(f);
GetMem(P, Size);
BlockRead(f, P^, Size);
B := P;
//
//
CRC := $FFFFFFFF;
for i := 1 to Size do
begin
CRC := CRC XOR B^;
Inc(B);
for j := 0 to 7 do
begin
flag := (CRC AND 1) > 0;
if flag then
CRC := (CRC SHR 1) XOR $04C11DB7
else
CRC := CRC SHR 1;
end;
end;
LabeledEdit1.Text := IntToHEX(CRC, 8);
//
//
Freemem(P);
CloseFile(f);
end;
lazarus crc32
lazarus crc32
asked Nov 14 '18 at 14:32
ClaireClaire
112
asked Nov 14 '18 at 14:32
ClaireClaire
112
edited Nov 14 '18 at 15:19
Claire
asked Nov 14 '18 at 14:32
ClaireClaire
112
asked Nov 14 '18 at 14:32
ClaireClaire
112
asked Nov 14 '18 at 14:32
ClaireClaire
112
112
We don't know what it is meant to do, and how it fails. You need to learn how to debug your program. That's your next task.
– David Heffernan
Nov 14 '18 at 14:47
my program just looking for checksum and finds wrong numbers. It checks .txt file where "123456789" and it finds "0x340BC6D9", but it must be "0xCBF43926". I already tried to debug as you said, but I have no idea what's problem here. That's why I asking here about my problem
– Claire
Nov 14 '18 at 15:17
There are many variants of CRC32 algorithm. Who knows which one you want? Presumably you do. You have working C code, and now want Pascal code. Compare the execution of the two versions (Pascal against C). Find out where the two diverge. Fix, and repeat. When there is no more divergence, the task is done. Once again, your next task it to learn how to debug. This is the perfect opportunity. Would you like to learn how to debug? Or do you just want code that works?
– David Heffernan
Nov 14 '18 at 15:20
I'd like to learn how to debug, I guess... okay then, I'll try once again
– Claire
Nov 14 '18 at 15:29
Just do what I say. Compare the execution of the two programs, the C version and the Pascal version. Output (e.g. to console) the value ofCRCeach time around the loop and compare the outputs of those two programs. Take it from there.
– David Heffernan
Nov 14 '18 at 15:32
|
show 2 more comments
We don't know what it is meant to do, and how it fails. You need to learn how to debug your program. That's your next task.
– David Heffernan
Nov 14 '18 at 14:47
my program just looking for checksum and finds wrong numbers. It checks .txt file where "123456789" and it finds "0x340BC6D9", but it must be "0xCBF43926". I already tried to debug as you said, but I have no idea what's problem here. That's why I asking here about my problem
– Claire
Nov 14 '18 at 15:17
There are many variants of CRC32 algorithm. Who knows which one you want? Presumably you do. You have working C code, and now want Pascal code. Compare the execution of the two versions (Pascal against C). Find out where the two diverge. Fix, and repeat. When there is no more divergence, the task is done. Once again, your next task it to learn how to debug. This is the perfect opportunity. Would you like to learn how to debug? Or do you just want code that works?
– David Heffernan
Nov 14 '18 at 15:20
I'd like to learn how to debug, I guess... okay then, I'll try once again
– Claire
Nov 14 '18 at 15:29
Just do what I say. Compare the execution of the two programs, the C version and the Pascal version. Output (e.g. to console) the value ofCRCeach time around the loop and compare the outputs of those two programs. Take it from there.
– David Heffernan
Nov 14 '18 at 15:32
We don't know what it is meant to do, and how it fails. You need to learn how to debug your program. That's your next task.
– David Heffernan
Nov 14 '18 at 14:47
We don't know what it is meant to do, and how it fails. You need to learn how to debug your program. That's your next task.
– David Heffernan
Nov 14 '18 at 14:47
my program just looking for checksum and finds wrong numbers. It checks .txt file where "123456789" and it finds "0x340BC6D9", but it must be "0xCBF43926". I already tried to debug as you said, but I have no idea what's problem here. That's why I asking here about my problem
– Claire
Nov 14 '18 at 15:17
my program just looking for checksum and finds wrong numbers. It checks .txt file where "123456789" and it finds "0x340BC6D9", but it must be "0xCBF43926". I already tried to debug as you said, but I have no idea what's problem here. That's why I asking here about my problem
– Claire
Nov 14 '18 at 15:17
There are many variants of CRC32 algorithm. Who knows which one you want? Presumably you do. You have working C code, and now want Pascal code. Compare the execution of the two versions (Pascal against C). Find out where the two diverge. Fix, and repeat. When there is no more divergence, the task is done. Once again, your next task it to learn how to debug. This is the perfect opportunity. Would you like to learn how to debug? Or do you just want code that works?
– David Heffernan
Nov 14 '18 at 15:20
There are many variants of CRC32 algorithm. Who knows which one you want? Presumably you do. You have working C code, and now want Pascal code. Compare the execution of the two versions (Pascal against C). Find out where the two diverge. Fix, and repeat. When there is no more divergence, the task is done. Once again, your next task it to learn how to debug. This is the perfect opportunity. Would you like to learn how to debug? Or do you just want code that works?
– David Heffernan
Nov 14 '18 at 15:20
I'd like to learn how to debug, I guess... okay then, I'll try once again
– Claire
Nov 14 '18 at 15:29
I'd like to learn how to debug, I guess... okay then, I'll try once again
– Claire
Nov 14 '18 at 15:29
Just do what I say. Compare the execution of the two programs, the C version and the Pascal version. Output (e.g. to console) the value of
CRC each time around the loop and compare the outputs of those two programs. Take it from there.– David Heffernan
Nov 14 '18 at 15:32
Just do what I say. Compare the execution of the two programs, the C version and the Pascal version. Output (e.g. to console) the value of
CRC each time around the loop and compare the outputs of those two programs. Take it from there.– David Heffernan
Nov 14 '18 at 15:32
|
show 2 more comments
2 Answers
2
active
oldest
votes
3
0xCBF43926 is the bit-wise inverse ("not") of 0x340BC6D9. You just need to use not on the result, or exclusive or with $FFFFFFFF.
answered Nov 14 '18 at 16:26
Mark AdlerMark Adler
58.3k864111
add a comment |
1
Note that FPC comes with a CRC32 unit. (derived from crc32.c by Mark Adler, above )
This unit has a function to calculate the CRC for a block called crc32()
function crc32 (crc : cardinal; buf : Pbyte; len : cardinal): cardinal;
The XOR is included in this crc32.crc32() function.
answered Nov 15 '18 at 10:32
Marco van de VoortMarco van de Voort
22.2k44079
add a comment |
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2 Answers
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active
oldest
votes
2 Answers
2
active
oldest
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votes
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votes
3
0xCBF43926 is the bit-wise inverse ("not") of 0x340BC6D9. You just need to use not on the result, or exclusive or with $FFFFFFFF.
answered Nov 14 '18 at 16:26
Mark AdlerMark Adler
58.3k864111
add a comment |
3
0xCBF43926 is the bit-wise inverse ("not") of 0x340BC6D9. You just need to use not on the result, or exclusive or with $FFFFFFFF.
answered Nov 14 '18 at 16:26
Mark AdlerMark Adler
58.3k864111
add a comment |
3
3
3
0xCBF43926 is the bit-wise inverse ("not") of 0x340BC6D9. You just need to use not on the result, or exclusive or with $FFFFFFFF.
answered Nov 14 '18 at 16:26
Mark AdlerMark Adler
58.3k864111
0xCBF43926 is the bit-wise inverse ("not") of 0x340BC6D9. You just need to use not on the result, or exclusive or with $FFFFFFFF.
answered Nov 14 '18 at 16:26
Mark AdlerMark Adler
58.3k864111
answered Nov 14 '18 at 16:26
Mark AdlerMark Adler
58.3k864111
answered Nov 14 '18 at 16:26
Mark AdlerMark Adler
58.3k864111
answered Nov 14 '18 at 16:26
Mark AdlerMark Adler
58.3k864111
58.3k864111
add a comment |
add a comment |
1
Note that FPC comes with a CRC32 unit. (derived from crc32.c by Mark Adler, above )
This unit has a function to calculate the CRC for a block called crc32()
function crc32 (crc : cardinal; buf : Pbyte; len : cardinal): cardinal;
The XOR is included in this crc32.crc32() function.
answered Nov 15 '18 at 10:32
Marco van de VoortMarco van de Voort
22.2k44079
add a comment |
1
Note that FPC comes with a CRC32 unit. (derived from crc32.c by Mark Adler, above )
This unit has a function to calculate the CRC for a block called crc32()
function crc32 (crc : cardinal; buf : Pbyte; len : cardinal): cardinal;
The XOR is included in this crc32.crc32() function.
answered Nov 15 '18 at 10:32
Marco van de VoortMarco van de Voort
22.2k44079
add a comment |
1
1
1
Note that FPC comes with a CRC32 unit. (derived from crc32.c by Mark Adler, above )
This unit has a function to calculate the CRC for a block called crc32()
function crc32 (crc : cardinal; buf : Pbyte; len : cardinal): cardinal;
The XOR is included in this crc32.crc32() function.
answered Nov 15 '18 at 10:32
Marco van de VoortMarco van de Voort
22.2k44079
Note that FPC comes with a CRC32 unit. (derived from crc32.c by Mark Adler, above )
This unit has a function to calculate the CRC for a block called crc32()
function crc32 (crc : cardinal; buf : Pbyte; len : cardinal): cardinal;
The XOR is included in this crc32.crc32() function.
answered Nov 15 '18 at 10:32
Marco van de VoortMarco van de Voort
22.2k44079
answered Nov 15 '18 at 10:32
Marco van de VoortMarco van de Voort
22.2k44079
answered Nov 15 '18 at 10:32
Marco van de VoortMarco van de Voort
22.2k44079
answered Nov 15 '18 at 10:32
Marco van de VoortMarco van de Voort
22.2k44079
22.2k44079
add a comment |
add a comment |
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We don't know what it is meant to do, and how it fails. You need to learn how to debug your program. That's your next task.
– David Heffernan
Nov 14 '18 at 14:47
my program just looking for checksum and finds wrong numbers. It checks .txt file where "123456789" and it finds "0x340BC6D9", but it must be "0xCBF43926". I already tried to debug as you said, but I have no idea what's problem here. That's why I asking here about my problem
– Claire
Nov 14 '18 at 15:17
There are many variants of CRC32 algorithm. Who knows which one you want? Presumably you do. You have working C code, and now want Pascal code. Compare the execution of the two versions (Pascal against C). Find out where the two diverge. Fix, and repeat. When there is no more divergence, the task is done. Once again, your next task it to learn how to debug. This is the perfect opportunity. Would you like to learn how to debug? Or do you just want code that works?
– David Heffernan
Nov 14 '18 at 15:20
I'd like to learn how to debug, I guess... okay then, I'll try once again
– Claire
Nov 14 '18 at 15:29
Just do what I say. Compare the execution of the two programs, the C version and the Pascal version. Output (e.g. to console) the value of
CRCeach time around the loop and compare the outputs of those two programs. Take it from there.– David Heffernan
Nov 14 '18 at 15:32