bitarithm.h File Reference

Helper functions for bit arithmetic. More...

Detailed Description

Helper functions for bit arithmetic.

Author

Kaspar Schleiser kaspa.nosp@m.r@sc.nosp@m.hleis.nosp@m.er.d.nosp@m.e

Martine Lenders mlend.nosp@m.ers@.nosp@m.inf.f.nosp@m.u-be.nosp@m.rlin..nosp@m.de

Definition in file bitarithm.h.

#include <stdint.h>
#include "cpu_conf.h"

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Macros
#define	ARCH_32_BIT   (__INT_MAX__ == 2147483647)
	1 for 32 bit architectures, 0 otherwise

Functions
static unsigned	bitarithm_msb (unsigned v)
	Returns the number of the highest '1' bit in a value. More...
static unsigned	bitarithm_lsb (unsigned v)
	Returns the number of the lowest '1' bit in a value. More...
unsigned	bitarithm_bits_set (unsigned v)
	Returns the number of bits set in a value. More...
uint8_t	bitarithm_bits_set_u32 (uint32_t v)
	Returns the (uint32_t version) number of bits set in a value. More...
unsigned	bitarith_msb_32bit_no_native_clz (unsigned v)
	Returns the number of the highest '1' bit in a value. More...
static uint8_t	bitarithm_clzb (uint8_t x)
	Returns the number of leading 0-bits in x, starting at the most significant bit position. More...
static unsigned	bitarithm_test_and_clear (unsigned state, uint8_t *index)
	Used for iterating over the bits in state. More...
#define	SETBIT(val, bit)   val |= (bit)
	Sets a bitmask for a bitfield. More...
#define	CLRBIT(val, bit)   val &= (~(bit))
	Clears bitmask for a bitfield. More...

Single Bit Defines
#define	BIT0   0x00000001
	Bit 0 set define.
#define	BIT1   0x00000002
	Bit 1 set define.
#define	BIT2   0x00000004
	Bit 2 set define.
#define	BIT3   0x00000008
	Bit 3 set define.
#define	BIT4   0x00000010
	Bit 4 set define.
#define	BIT5   0x00000020
	Bit 5 set define.
#define	BIT6   0x00000040
	Bit 6 set define.
#define	BIT7   0x00000080
	Bit 7 set define.
#define	BIT8   0x00000100
	Bit 8 set define.
#define	BIT9   0x00000200
	Bit 9 set define.
#define	BIT10   0x00000400
	Bit 10 set define.
#define	BIT11   0x00000800
	Bit 11 set define.
#define	BIT12   0x00001000
	Bit 12 set define.
#define	BIT13   0x00002000
	Bit 13 set define.
#define	BIT14   0x00004000
	Bit 14 set define.
#define	BIT15   0x00008000
	Bit 15 set define.
#define	BIT16   0x00010000
	Bit 16 set define.
#define	BIT17   0x00020000
	Bit 17 set define.
#define	BIT18   0x00040000
	Bit 18 set define.
#define	BIT19   0x00080000
	Bit 19 set define.
#define	BIT20   0x00100000
	Bit 20 set define.
#define	BIT21   0x00200000
	Bit 21 set define.
#define	BIT22   0x00400000
	Bit 22 set define.
#define	BIT23   0x00800000
	Bit 23 set define.
#define	BIT24   0x01000000
	Bit 24 set define.
#define	BIT25   0x02000000
	Bit 25 set define.
#define	BIT26   0x04000000
	Bit 26 set define.
#define	BIT27   0x08000000
	Bit 27 set define.
#define	BIT28   0x10000000
	Bit 28 set define.
#define	BIT29   0x20000000
	Bit 29 set define.
#define	BIT30   0x40000000
	Bit 30 set define.
#define	BIT31   0x80000000
	Bit 31 set define.

Macro Definition Documentation

CLRBIT

#define CLRBIT	(		val,
			bit
	)		val &= (~(bit))

Clears bitmask for a bitfield.

Parameters

[in]	val	The bitfield
[in]	bit	Specifies the bits to be cleared

Returns

The modified bitfield

Definition at line 52 of file bitarithm.h.

SETBIT

#define SETBIT	(		val,
			bit
	)		val |= (bit)

Sets a bitmask for a bitfield.

Parameters

[in]	val	The bitfield
[in]	bit	Specifies the bits to be set

Returns

The modified bitfield

Definition at line 41 of file bitarithm.h.

Function Documentation

bitarith_msb_32bit_no_native_clz()

unsigned bitarith_msb_32bit_no_native_clz

(

unsigned

v

)

Returns the number of the highest '1' bit in a value.

     Internal software implementation for 32 bit platforms,
     use @see bitarithm_msb in application code.

Parameters

[in]

v

Input value

Returns

Bit Number

bitarithm_bits_set()

unsigned bitarithm_bits_set

(

unsigned

v

)

Returns the number of bits set in a value.

Parameters

[in]

v

Input value with platform-dependent word size

Returns

Number of set bits

bitarithm_bits_set_u32()

uint8_t bitarithm_bits_set_u32

(

uint32_t

v

)

Returns the (uint32_t version) number of bits set in a value.

Parameters

[in]

v

Input value with 32 bit size

Returns

Number of set bits

bitarithm_clzb()

static uint8_t bitarithm_clzb ( uint8_t  x )

inlinestatic

Returns the number of leading 0-bits in x, starting at the most significant bit position.

If x is 0, the result is undefined.

Parameters

[in]

x

Input value

Returns

Number of leading zero bits

Definition at line 176 of file bitarithm.h.

bitarithm_lsb()

static unsigned bitarithm_lsb ( unsigned  v )

inlinestatic

Returns the number of the lowest '1' bit in a value.

Parameters

[in]

v

Input value - must be unequal to '0', otherwise the function will produce an infinite loop

Returns

Bit Number

Definition at line 206 of file bitarithm.h.

bitarithm_msb()

static unsigned bitarithm_msb ( unsigned  v )

inlinestatic

Returns the number of the highest '1' bit in a value.

Parameters

[in]

v

Input value

Returns

Bit Number

Source: http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogObvious

Definition at line 153 of file bitarithm.h.

bitarithm_test_and_clear()

static unsigned bitarithm_test_and_clear ( unsigned  state, uint8_t *  index  )

inlinestatic

Used for iterating over the bits in state.

Returns the index of a set bit in state, returns state with that bit cleared.

Warning

This is a low-level helper function, arguments are not checked. It is intended to iterate over a bit map until all bits are cleared. Whether it starts with the highest or lowest bit will depend on what is fastest on the given hardware.

state must not be zero.

Parameters

[in]	state	Bit Map with at least one bit set
[out]	index	Index of the first set bit. Must be initialized with 0 before the first call to this function, must not be modified between subsequent calls.

Returns

new state value - must be treated as opaque value

Definition at line 254 of file bitarithm.h.