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MdePkg/BaseLib: Fix CRC16-ANSI calculation 

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4609

The current CalculateCrc16Ansi implementation does the following:
1) Invert the passed checksum
2) Calculate the new checksum by going through data and using the
   lookup table
3) Invert it back again

This emulated my design for CalculateCrc32c, where 0 is
passed as the initial checksum, and it inverts in the end.
However, CRC16 does not invert the checksum on input and output.
So this is incorrect.

Fix the problem by not inverting input checksums nor output checksums.
Callers should now pass CRC16ANSI_INIT as the initial value instead of
"0". This is a breaking change.

This problem was found out-of-list when older ext4 filesystems
(that use crc16 checksums) failed to mount with "corruption".

Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
Signed-off-by: Pedro Falcato <pedro.falcato@gmail.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>
This commit is contained in:
Pedro Falcato 2023-11-30 02:46:10 +00:00 committed by mergify[bot]
parent 7182621edc
commit e2d4f75913
2 changed files with 7 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
MdePkg/Include/Library/BaseLib.h
View File

@ -4599,6 +4599,11 @@ CalculateCrc16Ansi (
IN UINT16 InitialValue
);
//
// Initial value for the CRC16-ANSI algorithm, when no prior checksum has been calculated.
//
#define CRC16ANSI_INIT 0xffff
/**
Calculates the CRC32c checksum of the given buffer.

4
MdePkg/Library/BaseLib/CheckSum.c
View File

@ -678,13 +678,13 @@ CalculateCrc16Ansi (
Buf = Buffer;
Crc = ~InitialValue;
Crc = InitialValue;
while (Length-- != 0) {
Crc = mCrc16LookupTable[(Crc & 0xFF) ^ *(Buf++)] ^ (Crc >> 8);
}
return ~Crc;
return Crc;
}
GLOBAL_REMOVE_IF_UNREFERENCED STATIC CONST UINT32 mCrc32cLookupTable[256] = {