Utilities for bit-twiddling. More...

Functions
template<typename T >
constexpr bool	sp::bitIsSet (T x, int bit)
	Return true iff the `bit`th bit of `x` is 1. More...

template<typename T >
constexpr T	sp::setBit (T x, int bit)
	Set a bit in `x` to 1, returning the result. More...

template<typename T >
constexpr T	sp::clearBit (T x, int bit)
	Set a bit in `x` to 0, returning the result. More...

template<typename T >
constexpr T	sp::assignBit (T x, int bit, bool value)
	Set bit `bit` of `x` to `value ? 1 : 0`, and return the result. More...

template<typename T >
constexpr T	sp::keepHighBits (T x, int KeepBits)
	Zero everything except the `KeepBits`-many high bits in x. More...

template<typename T >
constexpr T	sp::keepLowBits (T x, int KeepBits)
	Zero everything except the `KeepBits`-many low bits in x. More...

template<typename T = uint64_t, typename ValueT >
constexpr T	sp::bitfieldExtract (ValueT x, int start, int len=sizeof(T) *8)
	Extract a bitfield starting at bit `start` and extending for `len` bits. More...

template<typename ValueT , typename PayloadT >
constexpr ValueT	sp::bitfieldInsert (ValueT x, PayloadT value, int start, int len=bits< PayloadT >)
	Copy the least significant `len` bits of `value` into `x` at position `start`. More...

template<typename T >
constexpr T	sp::snipBit (T x, int bit)
	"cut" a bit out of x, shifting everything above it to the right. More...

template<typename I >
constexpr int	sp::bitsNeededForValue (I n)
	Calculate the number of bits needed to represent the given integer. More...

template<typename I >
constexpr I	sp::getLSBOnes (int count)
	Get a value with the count least significant bits set to one. More...

template<typename T >
constexpr T	sp::popcount (const T &arg)
	Population-count the object representation of any type. More...

Detailed Description

Utilities for bit-twiddling.

Convenient ways to access BFI and BFE instructions for GPUs.
Various other bit-smashing functions...

Function Documentation

◆ assignBit()

template<typename T >

constexpr T sp::assignBit	(	T	x,
		int	bit,
		bool	value
	)

constexpr

Set bit bit of x to value ? 1 : 0, and return the result.

◆ bitfieldExtract()

template<typename T = uint64_t, typename ValueT >

constexpr T sp::bitfieldExtract	(	ValueT	x,
		int	start,
		int	len = `sizeof(T) * 8`
	)

constexpr

Extract a bitfield starting at bit start and extending for len bits.

The result is shifted down to the least-significant position and returned.

Note that although this function looks hideously complicated, it does reliably compile to a BFE or an AND instruction, meaning you can safely use it to do bounds-checked bit-twiddling and so on.

Template Parameters

T	The type of the bifield member being extracted.
ValueT	The type of integer containing the bitfield (deduced)

◆ bitfieldInsert()

template<typename ValueT , typename PayloadT >

constexpr ValueT sp::bitfieldInsert	(	ValueT	x,
		PayloadT	value,
		int	start,
		int	len = `bits<PayloadT>`
	)

constexpr

Copy the least significant len bits of value into x at position start.

◆ bitIsSet()

template<typename T >

constexpr bool sp::bitIsSet	(	T	x,
		int	bit
	)

constexpr

Return true iff the bitth bit of x is 1.

◆ bitsNeededForValue()

template<typename I >

constexpr int sp::bitsNeededForValue ( I n )

constexpr

Calculate the number of bits needed to represent the given integer.

For non-negative values, this calculates log2(n + 1) rounded up to the nearest integer. For negative values, this gives the number of bits in the integer's type.

Parameters

n	An integer parameter for the calculation.

Returns: The number of bits required to represent n.

◆ clearBit()

template<typename T >

constexpr T sp::clearBit	(	T	x,
		int	bit
	)

constexpr

Set a bit in x to 0, returning the result.

The operation occurs in the type of x: T.

Template Parameters

T	The type of `x`, and the result.

Parameters

x	The input value.
bit	The position of the bit to clear.

Returns: A copy of x with the bit'th bit set to 1.

◆ getLSBOnes()

template<typename I >

constexpr I sp::getLSBOnes ( int count )

constexpr

Get a value with the count least significant bits set to one.

This computation is performed without wrapping (for constexpr computation), but is not otherwise the most efficient.

◆ keepHighBits()

template<typename T >

constexpr T sp::keepHighBits	(	T	x,
		int	KeepBits
	)

constexpr

Zero everything except the KeepBits-many high bits in x.

◆ keepLowBits()

template<typename T >

constexpr T sp::keepLowBits	(	T	x,
		int	KeepBits
	)

constexpr

Zero everything except the KeepBits-many low bits in x.

◆ popcount()

template<typename T >

constexpr T sp::popcount ( const T & arg )

constexpr

Population-count the object representation of any type.

If the input type contains any padding bytes, the function will become nondeterminstic (since any number of the padding bits might be 1). Nevertheless, the behaviour is in that case still defined and could conceivably be useful.

◆ setBit()

template<typename T >

constexpr T sp::setBit	(	T	x,
		int	bit
	)

constexpr

Set a bit in x to 1, returning the result.

The operation occurs in the type of x: T.

Template Parameters

T	The type of `x`, and the result.

Parameters

x	The input value.
bit	The position of the bit to set.

Returns: A copy of x with the bit'th bit set to 1.

◆ snipBit()

template<typename T >

constexpr T sp::snipBit	(	T	x,
		int	bit
	)

constexpr

"cut" a bit out of x, shifting everything above it to the right.

Functions

Detailed Description

Function Documentation

◆ assignBit()

◆ bitfieldExtract()

◆ bitfieldInsert()

◆ bitIsSet()

◆ bitsNeededForValue()

◆ clearBit()

◆ getLSBOnes()

◆ keepHighBits()

◆ keepLowBits()

◆ popcount()

◆ setBit()

◆ snipBit()