Difference between revisions of "Kim Walisch"

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=Population Count=
 
=Population Count=
Kim Walisch provides a header-only [[C]]/[[Cpp|C++]] library for [[Population Count|counting the number of 1 bits]] using specialized instructions of various processor architectures <ref>[https://github.com/kimwalisch/libpopcnt GitHub - kimwalisch/libpopcnt: Fast C/C++ bit population count library]</ref>, performing algorithms as described by [[Wojciech Muła]] et al. <ref>[[Wojciech Muła]], [http://dblp.uni-trier.de/pers/hd/k/Kurz:Nathan Nathan Kurz], [https://github.com/lemire Daniel Lemire] ('''2016'''). ''Faster Population Counts Using AVX2 Instructions''. [https://arxiv.org/abs/1611.07612 arXiv:1611.07612]</ref>.
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Kim Walisch provides a header-only [[C]]/[[Cpp|C++]] library for [[Population Count|counting the number of 1 bits]] using specialized instructions of various processor architectures <ref>[https://github.com/kimwalisch/libpopcnt GitHub - kimwalisch/libpopcnt: Fast C/C++ bit population count library]</ref>, performing algorithms as described by [[Wojciech Muła]] et al. <ref>[[Wojciech Muła]], [https://dblp.uni-trier.de/pers/hd/k/Kurz:Nathan Nathan Kurz], [https://github.com/lemire Daniel Lemire] ('''2016'''). ''Faster Population Counts Using AVX2 Instructions''. [https://arxiv.org/abs/1611.07612 arXiv:1611.07612]</ref>.
  
 
=External Links=
 
=External Links=
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'''[[People|Up one level]]'''
 
'''[[People|Up one level]]'''
[[Category:Programmer]]
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[[Category:Programmer|Walisch]]

Latest revision as of 18:54, 27 August 2019

Home * People * Kim Walisch

Kim Walisch,
a software engineer from Luxembourg, and avocational expert in prime number generation [1] [2], applying the Sieve of Eratosthenes [3]. He is knowledgeable about processor architectures, software optimization and bit-twiddling.

Bitscan

In October 2012, Kim Walisch proposed an improved bitscan routine, multiplying the De Bruijn Sequence with a 0-1 mask separated by the least significant one bit of a scanned integer or bitboard. The mask separation is cheaper than the bit isolation due to the x86 lea instruction, performing the decrement of a source register into another target register, not affecting processor flags. This is a 32-bit bitscan forward routine:

const int index32[32] = {
    0,  9,  1, 10, 13, 21,  2, 29, 
   11, 14, 16, 18, 22, 25,  3, 30,
    8, 12, 20, 28, 15, 17, 24,  7,
   19, 27, 23,  6, 26,  5,  4, 31
};

/**
 * bitScanForward
 * @author Kim Walisch (2012)
 * @param v 32-bit set
 * @precondition v != 0
 * @return index (0..31) of least significant one bit
 */
int bitScanForward(unsigned int v) {
   return index32[((v ^ (v - 1)) * 0x07C4ACDDU) >> 27];
}

Population Count

Kim Walisch provides a header-only C/C++ library for counting the number of 1 bits using specialized instructions of various processor architectures [4], performing algorithms as described by Wojciech Muła et al. [5].

External Links

GitHub - kimwalisch/libpopcnt: Fast C/C++ bit population count library by Kim Walisch

References

Up one level