Kim Walisch

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Kim Walisch, a software engineer from Luxembourg, and avocational expert in prime number generation, applying the Sieve of Eratosthenes. 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, performing algorithms as described by Wojciech Muła et al..

=External Links=
 * Referent Kim Walisch www.primzahlen.de (German)
 * kimwalisch (Kim Walisch) · GitHub
 * GitHub - kimwalisch/libpopcnt: Fast C/C++ bit population count library by Kim Walisch

=References= Up one level