57 lines
1.5 KiB
C++
57 lines
1.5 KiB
C++
#ifndef INCLUDE_GUARD_BIT_UTILS_H
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#define INCLUDE_GUARD_BIT_UTILS_H
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#include <cstdint> // uint32_t, uint64_t
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/**
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* Computes the parity of a 32-bit word (0 for even bit count and 1 otherwise)
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*/
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int bitParity(uint32_t x);
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/**
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* Counts the number of set bits (`1`s in binary) in the number `x`
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*/
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int bitCount(uint32_t x);
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/**
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* Gets the index of the LSB (least significant bit) in a 32-bit word
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*
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* @condition `x != 0`, for `x == 0` undefined behaviour
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*/
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int bitScanLS(uint32_t x);
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/**
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* 32-bit Parallel DEPosit (aka PDEP)
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*
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* Writes the `val` bits into the positions of the set bits in `mask`.
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*
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* Example:
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* val: **** **** **** 1.1.
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* mask: 1... 1... 1... 1...
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* res: 1... .... 1... ....
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*/
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uint32_t bitDeposit(uint32_t val, uint32_t mask);
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/**
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* Gets the next lexicographically ordered permutation of an n-bit word.
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*
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* Let `val` be a bit-word with `n` bits set, then this procedire computes a
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* `n` bit word wich is the next element in the lexicographically ordered
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* sequence of `n` bit words. For example
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*
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* val -> bitNextPerm(val)
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* 00010011 -> 00010101
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* 00010101 -> 00010110
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* 00010110 -> 00011001
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* 00011001 -> 00011010
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* 00011010 -> 00011100
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* 00011100 -> 00100011
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*
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* @condition `x != 0`, for `x == 0` undefined behaviour due to `bitScanLS`
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*
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* see: https://graphics.stanford.edu/~seander/bithacks.html#NextBitPermutation
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*/
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uint32_t bitNextPerm(uint32_t val);
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#endif /* BIT_UTILS_INCLUDE_GUARD_H */
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