algo_bit.md

Bit algorithms

The namespace algo::bit offers a set of bit manipulation algorithms. They can help when the number of operations is required to be low or when to avoid importing other libraries so save space.

The algorithms

These functions are constexpr lambda-functions in a header-file. Using them should allow the compiler to determine sizes in compile-time.

Check sign of an input number

constexpr auto Sign = [](const auto& x);

Returns 0 if x is positive otherwise -1.

Usage

int sign{algo::bit::Sign(-1)};

Check if an input is even

constexpr auto IsEven = [](const auto& x);

Returns true if x is even, false if odd.

Usage

bool even{algo::bit::IsEven(2)};

Set a specific bit

constexpr auto SetBit = [](const auto& x, const auto& n, const Bit& b);

Changes x at bit position n to either 0 or 1.

Example

unsigned int num{algo::bit::SetBit(0xFFFFF, 15, algo::bit::Bit::False)}; // == 0xF7FFF

Check if a bit is set

constexpr auto IsBit = [](const auto& x, const auto& n);

Returns true if bit number n in x is 1, otherwise false.

Example

bool is_bit{algo::bit::IsBit(0xAAAA, 11)}; // == true

Toogle a bit

constexpr auto ToggleBit = [](const auto& x, const auto& n);

Changes a bit at position n in x, zero to one or one to zero.

Example

unsigned int{algo::bit::ToggleBit(0xBBBB, 14)}; // == 0xFBBB

Check if a number is a power of 2

constexpr auto IsPow2 = [](const auto& x);

Returns true if x is a power of two, e.g. is a power of 2.

Example

bool is_pow2{algo::bit::IsPow2(1024)}; // ==  true

.

Get the next power of 2

constexpr auto NextPow2 = [](auto x);

Returns the next power of two, e.g. the next power of two of 1025 is 2048.

Example

unsigned int next_pow2{algo::bit::NextPow2(1025)}; // == 2048

Count number of 1s in a number

constexpr auto CountSetBits = [](auto x);

Returns the number of set bits, the number of 1s, in a (binary) number.

Example

unsigned count{algo::bit::CountSetBits(0xFF)}; // == 8

Swap the bits in a number

constexpr auto SwapBits = [](const auto& x);

Changes all the true bits to false, and all false bit to true in the input number x.

Example

unsigned int swapped{algo::bit::SwapBits(170)}; // == 85