Bits and bit fields

Bit, mask and register field macros. More...

Macros
#define	PBL_BIT(n)   (1U << (n))
	Unsigned 32-bit value with a single bit set.
#define	PBL_BIT64(n)   (1ULL << (n))
	Unsigned 64-bit value with a single bit set.
#define	PBL_BIT_MASK(n)   (PBL_BIT(n) - 1U)
	Unsigned 32-bit mask with the n least significant bits set.
#define	PBL_BIT64_MASK(n)   (PBL_BIT64(n) - 1ULL)
	Unsigned 64-bit mask with the n least significant bits set.
#define	PBL_GENMASK(h, l)   (((2U << ((h) - (l))) - 1U) << (l))
	Unsigned 32-bit mask with bits l to h set, both included.
#define	PBL_GENMASK64(h, l)   (((2ULL << ((h) - (l))) - 1ULL) << (l))
	Unsigned 64-bit mask with bits l to h set, both included.
#define	PBL_LSB_GET(value)   ((value) & -(value))
	Isolate the least significant set bit of a value.
#define	PBL_FIELD_GET(mask, value)   (((value) & (mask)) / PBL_LSB_GET(mask))
	Extract a field from a register value.
#define	PBL_FIELD_PREP(mask, value)   (((value) * PBL_LSB_GET(mask)) & (mask))
	Prepare a field value for a register.
#define	PBL_WRITE_BIT(var, bit, set)
	Set or clear a bit in a variable.

Detailed Description

Bit, mask and register field macros.

A field is described by a contiguous mask, usually built with PBL_GENMASK(). PBL_FIELD_PREP() shifts a value into the field and PBL_FIELD_GET() extracts it, so the field position never has to be spelled out. With a constant mask both fold to a plain shift and mask.

#define CTRL1_ODR_MASK  PBL_GENMASK(7, 4)
#define CTRL1_ODR_50HZ  0x4U
#define CTRL1_LP_EN     PBL_BIT(0)
 
reg = PBL_FIELD_PREP(CTRL1_ODR_MASK, CTRL1_ODR_50HZ) | CTRL1_LP_EN;
odr = PBL_FIELD_GET(CTRL1_ODR_MASK, reg);

Macro Definition Documentation

PBL_BIT

#define PBL_BIT

(

n

)

(1U << (n))

Unsigned 32-bit value with a single bit set.

Parameters

n	Bit position, 0 to 31.

PBL_BIT64

#define PBL_BIT64

(

n

)

(1ULL << (n))

Unsigned 64-bit value with a single bit set.

Parameters

n	Bit position, 0 to 63.

PBL_BIT64_MASK

#define PBL_BIT64_MASK

(

n

)

(PBL_BIT64(n) - 1ULL)

Unsigned 64-bit mask with the n least significant bits set.

Parameters

n	Number of bits, 0 to 63.

PBL_BIT_MASK

#define PBL_BIT_MASK

(

n

)

(PBL_BIT(n) - 1U)

Unsigned 32-bit mask with the n least significant bits set.

Parameters

n	Number of bits, 0 to 31.

PBL_FIELD_GET

#define PBL_FIELD_GET	(		mask,
			value
	)		(((value) & (mask)) / PBL_LSB_GET(mask))

Extract a field from a register value.

Parameters

mask	Contiguous, non-zero field mask, evaluated twice.
value	Register value.

Returns

Field value, shifted down to bit 0.

PBL_FIELD_PREP

#define PBL_FIELD_PREP	(		mask,
			value
	)		(((value) * PBL_LSB_GET(mask)) & (mask))

Prepare a field value for a register.

Parameters

mask	Contiguous, non-zero field mask, evaluated twice.
value	Field value; bits that do not fit the field are dropped.

Returns

value shifted into the field position and masked.

PBL_GENMASK

#define PBL_GENMASK	(		h,
			l
	)		(((2U << ((h) - (l))) - 1U) << (l))

Unsigned 32-bit mask with bits l to h set, both included.

Parameters

h	Most significant bit of the mask, 0 to 31.
l	Least significant bit of the mask, at most h.

PBL_GENMASK64

#define PBL_GENMASK64	(		h,
			l
	)		(((2ULL << ((h) - (l))) - 1ULL) << (l))

Unsigned 64-bit mask with bits l to h set, both included.

Parameters

h	Most significant bit of the mask, 0 to 63.
l	Least significant bit of the mask, at most h.

PBL_LSB_GET

#define PBL_LSB_GET

(

value

)

((value) & -(value))

Isolate the least significant set bit of a value.

Parameters

value

Unsigned value, evaluated twice.

Returns

value with every bit cleared but its lowest set one, or 0 if value is 0.

PBL_WRITE_BIT

#define PBL_WRITE_BIT	(		var,
			bit,
			set
	)

Value:

  ((var) =                           \
       (set) ? ((var) | ((__typeof__(var))1 << (bit))) : ((var) & ~((__typeof__(var))1 << (bit))))

Set or clear a bit in a variable.

The mask is built in the type of var, so other bits are preserved whatever its width.

Parameters

var	Unsigned integer variable to update, evaluated more than once.
bit	Bit position, less than the width of var.
set	Set the bit if true, clear it otherwise.