bits.h File Reference

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Classes
struct	CeilLog2< N >
struct	CeilLog2< 1 >
struct	CeilLog2< 0 >

Macros
#define	BIT(n)   (1u << (n))
	pretty much the same as Bit<unsigned>. More...
#define	IS_POW2(n)   (((n) != 0) && ((n) & ((n)-1)) == 0)
#define	ROUND_UP(n, multiple)   (((n) + (multiple)-1) & ~((multiple)-1))

Functions
template<typename T >
T	Bit (size_t n)
	value of bit number <n>. More...
template<typename T >
bool	IsBitSet (T value, size_t index)
template<typename T >
T	bit_mask (size_t numBits)
	a mask that includes the lowest N bits More...
template<typename T >
T	bits (T num, size_t lo_idx, size_t hi_idx)
	extract the value of bits hi_idx:lo_idx within num More...
template<typename T >
T	SetBitsTo (T num, size_t lo_idx, size_t hi_idx, size_t value)
	set the value of bits hi_idx:lo_idx More...
template<typename T >
size_t	SparsePopulationCount (T mask)
template<typename T >
static size_t	PopulationCount (T x)
template<typename T >
bool	is_pow2 (T n)
template<typename T >
T	LeastSignificantBit (T x)
template<typename T >
T	ClearLeastSignificantBit (T x)
template<typename T >
size_t	ceil_log2 (T x)
	ceil(log2(x)) More...
int	floor_log2 (const float x)
	floor(log2(f)) fast, uses the FPU normalization hardware. More...
template<typename T >
T	round_up_to_pow2 (T x)
	round up to next larger power of two. More...
template<typename T >
T	round_down_to_pow2 (T x)
	round down to next larger power of two. More...
template<typename T >
T	round_up (T n, T multiple)
	round number up/down to the next given multiple. More...
template<typename T >
T	round_down (T n, T multiple)
template<typename T >
T	MaxPowerOfTwoDivisor (T value)

Macro Definition Documentation

BIT

#define BIT

(

n

)

(1u << (n))

pretty much the same as Bit<unsigned>.

this is intended for the initialization of enum values, where a compile-time constant is required.

IS_POW2

#define IS_POW2

(

n

)

(((n) != 0) && ((n) & ((n)-1)) == 0)

ROUND_UP

#define ROUND_UP	(		n,
			multiple
	)		(((n) + (multiple)-1) & ~((multiple)-1))

Function Documentation

Bit()

template<typename T >

T Bit ( size_t  n )

inline

value of bit number <n>.

Parameters

n	bit index.

requirements:

• T should be an unsigned type
• n must be in [0, CHAR_BIT*sizeof(T)), else the result is undefined!

bit_mask()

template<typename T >

T bit_mask ( size_t  numBits )

inline

a mask that includes the lowest N bits

Parameters

numBits

Number of bits in mask.

bits()

template<typename T >

T bits ( T  num, size_t  lo_idx, size_t  hi_idx  )

inline

extract the value of bits hi_idx:lo_idx within num

example: bits(0x69, 2, 5) == 0x0A

Parameters

num	number whose bits are to be extracted
lo_idx	bit index of lowest bit to include
hi_idx	bit index of highest bit to include

Returns

value of extracted bits.

ceil_log2()

template<typename T >

size_t ceil_log2 ( T  x )

inline

ceil(log2(x))

Parameters

x	(unsigned integer)

Returns

ceiling of the base-2 logarithm (i.e. rounded up) or zero if the input is zero.

ClearLeastSignificantBit()

template<typename T >

T ClearLeastSignificantBit ( T  x )

inline

floor_log2()

int floor_log2

(

const float

x

)

floor(log2(f)) fast, uses the FPU normalization hardware.

Parameters

x	(float) input; MUST be > 0, else results are undefined.

Returns

floor of the base-2 logarithm (i.e. rounded down).

is_pow2()

template<typename T >

bool is_pow2 ( T  n )

inline

Returns

whether the given number is a power of two.

IsBitSet()

template<typename T >

bool IsBitSet ( T  value, size_t  index  )

inline

LeastSignificantBit()

template<typename T >

T LeastSignificantBit ( T  x )

inline

MaxPowerOfTwoDivisor()

template<typename T >

T MaxPowerOfTwoDivisor ( T  value )

inline

PopulationCount()

template<typename T >

static size_t PopulationCount ( T  x )

inlinestatic

Returns

number of 1-bits in mask. execution time is logarithmic in the total number of bits. supports up to 128-bit integers (if their arithmetic operators are defined). [http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel]

round_down()

template<typename T >

T round_down ( T  n, T  multiple  )

inline

round_down_to_pow2()

template<typename T >

T round_down_to_pow2 ( T  x )

inline

round down to next larger power of two.

round_up()

template<typename T >

T round_up ( T  n, T  multiple  )

inline

round number up/down to the next given multiple.

Parameters

n	Number to round.
multiple	Must be a power of two.

round_up_to_pow2()

template<typename T >

T round_up_to_pow2 ( T  x )

inline

round up to next larger power of two.

SetBitsTo()

template<typename T >

T SetBitsTo ( T  num, size_t  lo_idx, size_t  hi_idx, size_t  value  )

inline

set the value of bits hi_idx:lo_idx

Parameters

lo_idx	bit index of lowest bit to include
hi_idx	bit index of highest bit to include
value	new value to be assigned to these bits

SparsePopulationCount()

template<typename T >

size_t SparsePopulationCount ( T  mask )

inline

Returns

number of 1-bits in mask. execution time is proportional to number of 1-bits in mask.