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xxHash sometimes doesn't match the Hash from the C library from Google #16

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illcom94 opened this issue Aug 19, 2015 · 4 comments
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xxHash sometimes doesn't match the Hash from the C library from Google #16

illcom94 opened this issue Aug 19, 2015 · 4 comments

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@illcom94
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I need to be able to verify an xxHash64 that is being generated by another program. Sometimes the xxHash from this code doesn't match, and when I run the C code downloaded from google, it does.
https://code.google.com/p/xxhash/

Has anyone else had this issue?
@illcom94
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I stepped through the code along with the C++ code from google and I've found the issue.
xxHash.cs

  1. In ComputeHashInternal() the dataCount variable should be a long instead of an int. On large files, it overflows into negative.
  2. In PostProcess() you have an if statement "if ((remainder.Length % 8) > 4)" this ensures that your code for processing the last 4 bytes of a file will never be hit. It should be changed to " if ((remainder.Length % 8) == 4)".

After these two changes, everything seems to match.

@illcom94
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After running a few more files I had to make a modification to my #2 fix.
The if statement should be "if ((remainder.Length % 8) >= 4)"

@brandondahler
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I'll take a look at as soon as I can. If you know how to submit a pull request with the changes you talked about above, it could significantly help expedite the process.

brandondahler added a commit that referenced this issue Sep 5, 2015
@brandondahler
Issue #16 - xxHash Deviations
f9dd177 
xxHash calculated incorrect valuex when in 64-bit mode and the input satisfies: length % 8 == 4.
xxHash calculated incorrect values when in either mode and the input length was greater than or equal to 2^32 characters in length.

Both of these issues cause breaking changes to any current users of xxHash given the value(s) could satisfy those constraints.
brandondahler added a commit that referenced this issue Sep 5, 2015
@brandondahler
Issue #16 - xxHash Deviations
764edbe 
xxHash calculated incorrect valuex when in 64-bit mode and the input satisfies: length % 8 == 4.
xxHash calculated incorrect values when in either mode and the input length was greater than or equal to 2^32 characters in length.

Both of these issues cause breaking changes to any current users of xxHash given the value(s) could satisfy those constraints.
brandondahler added a commit that referenced this issue Sep 5, 2015
@brandondahler
Issue #16 - xxHash Deviations
165e3d5 
xxHash calculated incorrect valuex when in 64-bit mode and the input satisfies: length % 8 == 4.
xxHash calculated incorrect values when in either mode and the input length was greater than or equal to 2^31 characters in length.

Both of these issues cause breaking changes to any current users of xxHash given the value(s) could satisfy those constraints.
brandondahler added a commit that referenced this issue Sep 27, 2015
@brandondahler
Merge pull request #17 from brandondahler/bugfix/xxHash
9a464b9 
Issue #16 - xxHash Deviations
@brandondahler
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This issue has been addressed in release 1.8.1.

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@brandondahler @illcom94