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Use another implementation for PDEP #3

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Use another implementation for PDEP #3

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@yanjiew1 yanjiew1 commented Aug 12, 2024 •
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This approach is from chapter 7 of Hacker's Delight. It eliminates the need of POPCNT and BZHI instructions totally, enhancing portability.

GCC generates less instructions compared to the original implementation.

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Use another implementation for PDEP
4a46b90 
This approach is from chapter 7 of Hacker's Delight. It eliminates
the need of POPCNT and BZHI instructions totally, enhancing portability.

GCC generates less instructions compared to the original implementation.
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yanjiew1 commented Aug 14, 2024 •
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The performance can be slower when compiled with "-O3" flag because the new implementation cannot take advantage of the LEA instruction.
If we compile this code with "-O3", GCC may inline the function and then optimize the code in a way that the shifts of the ppp are computed once for each mask. Thus, the number of instructions may not be reduced when "-O3" is used.

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