Bit(field) macros

Modules
	Data routines

some EVIL bit-field operations, >:)
These allow you to mimic bitfields with macros. Most of the bitfields in the registers have foo_SHIFT and foo_SHIFT macros indicating the mask and shift values of the bitfield named foo in a variable. These macros let you prepare, get and set the bitfields.
INLINE u32	bf_get (u32 y, uint shift, uint len)
	Get len long bitfield from y, starting at shift.
INLINE u32	bf_merge (u32 y, u32 x, uint shift, uint len)
	Merge x into an len long bitfield from y, starting at shift.
INLINE u32	bf_clamp (int x, uint len)
	Clamp to within the range allowed by len bits.
INLINE int	bit_tribool (u32 flags, uint plus, uint minus)
	Gives a tribool (-1, 0, or +1) depending on the state of some bits.
INLINE u32	ROR (u32 x, uint ror)
	Rotate bits right. Yes, this does lead to a ror instruction.
#define	BFN_PREP(x, name)   ( ((x)<<name##_SHIFT) & name##_MASK )
	Prepare a named bit-field for for insterion or combination.
#define	BFN_GET(y, name)   ( ((y) & name##_MASK)>>name##_SHIFT )
	Get the value of a named bitfield from y. Equivalent to (var=) y.name.
#define	BFN_SET(y, x, name)   (y = ((y)&~name##_MASK) | BFN_PREP(x,name) )
	Set a named bitfield in y to x. Equivalent to y.name= x.
#define	BFN_CMP(y, x, name)   ( ((y)&name##_MASK) == (x) )
	Compare a named bitfield to named literal x.
#define	BFN_PREP2(x, name)   ( (x) & name##_MASK )
	Massage x for use in bitfield name with pre-shifted x.
#define	BFN_GET2(y, name)   ( (y) & name##_MASK )
	Get the value of bitfield name from y, but don't down-shift.
#define	BFN_SET2(y, x, name)   ( y = ((y)&~name##_MASK) | BFN_PREP2(x,name) )
	Set bitfield name from y to x with pre-shifted x.

Simple bit macros
#define	BIT(n)   ( 1<<(n) )
	Create value with bit n set.
#define	BIT_SHIFT(a, n)   ( (a)<<(n) )
	Shift a by n.
#define	BIT_MASK(len)   ( BIT(len)-1 )
	Create a bitmask len bits long.
#define	BIT_SET(y, flag)   ( y |= (flag) )
	Set the flag bits in word.
#define	BIT_CLEAR(y, flag)   ( y &= ~(flag) )
	Clear the flag bits in word.
#define	BIT_FLIP(y, flag)   ( y ^= (flag) )
	Flip the flag bits in word.
#define	BIT_EQ(y, flag)   ( ((y)&(flag)) == (flag) )
	Test whether all the flag bits in word are set.
#define	BF_MASK(shift, len)   ( BIT_MASK(len)<<(shift) )
	Create a bitmask of length len starting at bit shift.
#define	_BF_GET(y, shift, len)   ( ((y)>>(shift))&BIT_MASK(len) )
	Retrieve a bitfield mask of length starting at bit shift from y.
#define	_BF_PREP(x, shift, len)   ( ((x)&BIT_MASK(len))<<(shift) )
	Prepare a bitmask for insertion or combining.
#define	_BF_SET(y, x, shift, len)    ( y= ((y) &~ BF_MASK(shift, len)) | _BF_PREP(x, shift, len) )
	Insert a new bitfield value x into y.

Detailed Description

Function Documentation

bf_get()

INLINE u32 bf_get	(	u32	y,
		uint	shift,
		uint	len
	)

Get len long bitfield from y, starting at shift.

Parameters

y	Value containing bitfield.
shift	Bitfield Start;
len	Length of bitfield.

Returns

Bitfield between bits shift and shift + length.

bf_merge()

INLINE u32 bf_merge	(	u32	y,
		u32	x,
		uint	shift,
		uint	len
	)

Merge x into an len long bitfield from y, starting at shift.

Parameters

y	Value containing bitfield.
x	Value to merge (will be masked to fit).
shift	Bitfield Start;
len	Length of bitfield.

Returns

Result of merger: (y&~M) | (x<<s & M)

Note

Does not write the result back into y (Because pure C does't have references, that's why)

bit_tribool()

INLINE int bit_tribool	(	u32	flags,
		uint	plus,
		uint	minus
	)

Gives a tribool (-1, 0, or +1) depending on the state of some bits.

Looks at the plus and minus bits of flags, and subtracts their status to give a +1, -1 or 0 result. Useful for direction flags.

Parameters

flags	Value with bit-flags.
plus	Bit number for positive result.
minus	Bit number for negative result.

Returns

+1 if plus bit is set but minus bit isn't
-1 if minus bit is set and plus bit isn't
0 if neither or both are set.

Referenced by key_tri_fire(), key_tri_horz(), key_tri_shoulder(), and key_tri_vert().