Fix undefined behaviour of char bit shifting when combining classic i… #19
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* Expose classic_combine function * Add exposition code * Fix syntax error * Expose calc_signature_size
* Expose classic_combine function * Add exposition code * Fix syntax error * Expose calc_signature_size * Expose classic combine as cmd instead
…ndices Previously when combining multiple classic indices into a single classic index, the contents of source indices are read in as `char`. During the interleaving process, depending on the current position of the destination index, both left and right shifts on the next char could be performed. However, there are a few undefined behaviours that could affect the results depending on the platform: 1. The signedness of a `char` is an undefined behaviour. Hence when bit shifting, the usual arithmetic conversion performed on the char is undefined. The char could be promoted to either signed int or unsigned int. 2. If the char is treated as signed int, the bit shifting (both left and right) is also undefined in pre-c++20 standards. The behaviour is platform dependent. This change fixes the issue by declare the contents read from source indices as `unsigned char`.
…ne-cmd Modify combine cmd
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…ingmann#5) When combining classic indices, for each batch the combinations of rows from each constituent index are written to an output block. The output block is reused for next batch. As we use bitwise OR operation to combine rows from the constituent indices, the output block should be reset to all 0s before being reused. Otherwise, previous set bits will be carried over to next batch and accumulating false positives till the end of the batch processing loop.
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…ndices
Previously when combining multiple classic indices into a single classic
index, the contents of source indices are read in as
char. During theinterleaving process, depending on the current position of the destination
index, both left and right shifts on the next char could be performed.
However, there are a few undefined behaviours that could affect the results
depending on the platform:
charis an undefined behaviour. Hence whenbit shifting, the usual arithmetic conversion performed on the char is
undefined. The char could be promoted to either signed int or unsigned
int.
right) is also undefined in pre-c++20 standards. The behaviour is platform
dependent.
This change fixes the issue by declare the contents read from source
indices as
unsigned char.