bits.h File Reference

Bits and bitfields. More...

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Macros
#define	st_bf_set(word, mask, val)   (((word) & ~(mask)) | (val))
	Set a bitfield in a word to a new value.
#define	ST_BIT(pos)   (1 << (pos))
	Create a bitmask for a single bit.
#define	ST_BITMASK(hi, lo)   ((1 << (hi)) * 2 - (1 << (lo)))
	Create a contiguous bitmask.
#define	ST_BITFIELD(mask, val)   ((val) << (__builtin_ffs(mask) - 1))
	Create a bitfield.

Typedefs
typedef int	StBits
	The data type for bitwise operations.

Detailed Description

Bits and bitfields.

This header file provides macros for operating with bits and bitfields. Use the StBits data type for bitwise operations as it avoids many issues related to integral promotion, which is a common source of bugs when doing bit manipulations.

Note

Compiling with -Wconversion is recommended.

Usage.

1. Set.

   word |= ST_BIT(pos);
   word |= ST_BITMASK(hi, lo);

2. Clear.

   word &= ~ST_BIT(pos);
   word $= ~ST_BITMASK(hi, lo);

Macro Definition Documentation

st_bf_set

#define st_bf_set	(		word,
			mask,
			val
	)		(((word) & ~(mask)) | (val))

Set a bitfield in a word to a new value.

Parameters

[in]	word	The word that contains the bitfield.
[in]	mask	The bitmask of the bitfield.
[in]	val	The new value of the bitfield.

Returns

New value of the word.

ST_BIT

#define ST_BIT

(

pos

)

(1 << (pos))

Create a bitmask for a single bit.

This macro creates a bitmask for a bit at position pos.

Returns

A bitmask for the bit at the pos position.

ST_BITFIELD

#define ST_BITFIELD	(		mask,
			val
	)		((val) << (__builtin_ffs(mask) - 1))

Create a bitfield.

Parameters

[in]	mask	The bitmask of the bitfield.
[in]	val	The value of the bitfield.

Returns

A bitfield with the value val at the position of the mask.

ST_BITMASK

#define ST_BITMASK	(		hi,
			lo
	)		((1 << (hi)) * 2 - (1 << (lo)))

Create a contiguous bitmask.

This macro creates a contiguous bitmask that spans from the hi (most significant bit) to the lo (least significant bit).

Returns

A contiguous bitmask that spans from the hi to the lo.