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BFU.h File Reference

Bit Field Unpack Routines. More...

#include "PBS/FFS.ih"

Include dependency graph for BFU.h:

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Classes
struct	_BFU
	The return value of the BFU routines, capturing the current 32-bit word that is being used as a source and the extracted value. More...
Defines
#define	_bfu_get_pos(_bfu) _bfu.val
	Gets the current buffer bit position.
#define	_bfu_get_tmp(_bfu) _bfu.cur
	Gets the current temporary buffer.
#define	_bfu_get(_bfu, _tmp, _pos)
	Gets the current temporary buffer and buffer bit position.
#define	_bfu_put_tmp(_bfu, _tmp) _bfu.cur = _tmp;
	Updates the current temporary buffer.
#define	_bfu_put_pos(_bfu, _pos) _bfu.val = _pos;
	Gets the current buffer bit position.
#define	_bfu_put(_bfu, _tmp, _pos)
	Updates the current temporary buffer and buffer bit position.
#define	_bfu_construct(_bfu, _s, _alignment, _src, _boff)
	Constructs a BFU from an arbitrarily aligned source buffer pointer, and a bit offset _boff. Also returns a 32-bit aligned pointer to be used with _bfu_extract.
#define	_bfu_constructW(_bfu, _src, _boff)
	Constructs a BFU from an 32-bit (word) aligned source buffer pointer and a bit offset _boff.
#define	_bfu_extractBoolean(_bfu, _wrds, _position)
	Extracts the next bit, returning it as a boolean value. The justification is unspecfied. The implementation is the most efficient of _bfu_extractBL or _bfu_extractBR. Use one of those routine if the justification needs to be specified.
#define	_bfu_extractBR(_bfu, _wrds, _position)
	Extracts the right justified bit from the current position.
#define	_bfu_extractBL(_bfu, _wrds, _position)
	Extracts the left justified bit from the current position.
#define	_bfu_extractL(_bfu, _wrds, _position, _width)
	Extracts a left justified value from the current position.
#define	_bfu_extractR(_bfu, _wrds, _position, _width)
	Extracts a right justified value from the current position.
#define	_bfu_extract32(_bfu, _wrds, _position)
	Extracts 32 bits from the current position.
#define	_bfu_count1s(_bfu, _wrds, _position)
	Counts the number of 1s till the first clear bit.
#define	_bfu_revert(_bfu, _wrds, _position, _nwidth, _nexp)
	Counts the number of 1s till the first clear bit.
Typedefs
typedef struct _BFU	BFU
	Typedef for struct _BFU.
Functions
static __inline BFU	BFU__bitL (const unsigned int *wrds, unsigned int cur, unsigned int position)
	Unpacks the left justified bit from the current position.
static __inline BFU	BFU__bitR (const unsigned int *wrds, unsigned int cur, unsigned int position)
	Unpacks the right justified bit from the current position.
static __inline BFU	BFU__boolean (const unsigned int *wrds, unsigned int cur, unsigned int position)
	Unpacks the next bit. This is equivalent to a bit extract, but the justification (left or right) is unspecified. Rather the must efficient extraction is used, returning only 0 or non-zero. Use BFU__bitL or BFU__bitR if a specific justification is needed.
static __inline BFU	BFU__wordR (const unsigned int *wrds, unsigned int cur, unsigned int position, unsigned int width)
	Unpacks a right justified bit field from the current position. The width of the bit field must be less than 32 bits.
static __inline BFU	BFU__wordL (const unsigned int *wrds, unsigned int cur, unsigned int position, unsigned int width)
	Unpacks a left justified bit field from the current position. The width of the bit field must be less than 32 bits.
static __inline BFU	BFU__word (const unsigned int *wrds, unsigned int cur, unsigned int position)
	Unpacks exactly 32 bits from the current position.
static __inline BFU	BFU__ffc (const unsigned int *wrds, unsigned int cur, unsigned int position)
	Scans the input bit stream for the first clear bit, this effectively counts the number of set bits.

Detailed Description

Bit Field Unpack Routines.

Author:: JJRussell - russell@slac.stanford.edu

Inline functions to (left justified) unpack bit fields.

Define Documentation

#define _bfu_construct	(	_bfu,
		_s,
		_alignment,
		_src,
		_boff	)

Value:

do                                                                         \
{                                                                          \
    /* Move to the nearest 32-bit boundary */                              \
                                                                           \
    /* Convert to a 32-bit pointer */                                      \
    _s = (const unsigned int *)_src;                                       \
                                                                           \
    /* Calculate the number of bits that are not a multiple of 32 */       \
    alignment = ((int)_s & 0x3) << 3;                                      \
                                                                           \
    /* Add this to the bit offset */                                       \
    _boff += _alignment;                                                   \
                                                                           \
    /* Reset the pointer back to the nearest 32-bit boundary */            \
    _s = (const unsigned int *)((int)_s & ~0x3);                           \
                                                                           \
    /* Extract the first word */                                           \
    _bfu.cur = _s[_boff >> 5];                                             \
    _bfu.val = boff;                                                       \
                                                                           \
} while (0)

Constructs a BFU from an arbitrarily aligned source buffer pointer, and a bit offset _boff. Also returns a 32-bit aligned pointer to be used with _bfu_extract.

Parameters:

	_bfu	The BFU structure to populate
	_s	Returned as a 32-bit aligned version of _src
	_alignment	Returned as the alignment adjustment. This value should be subtracted off when resetting the bit offset back to a value that corresponds to the alignment associated with _src.
	_src	The source buffer pointer
	_boff	The original bit offset, returned as the adjusted offset to compensate for any possible alignment to _s

#define _bfu_constructW	(	_bfu,
		_src,
		_boff	)

Value:

_bfu.cur = _src[_boff >> 5];                                           \
    _bfu.val = _boff                                                       \

Constructs a BFU from an 32-bit (word) aligned source buffer pointer and a bit offset _boff.

Parameters:

	_bfu	The BFU structure to populate
	_src	The source buffer pointer
	_boff	The original bit offset, returned as the adjusted offset to compensate for any possible alignment to _s

#define _bfu_count1s	(	_bfu,
		_wrds,
		_position	)

Value:

(_bfu      = BFU__ffc (_wrds, _bfu_get_tmp(bfu), _position),       \
         _position += (_bfu.val -= _position),                             \
         _bfu.val - 1)

Counts the number of 1s till the first clear bit.

Returns:: The number of bits to the first clear bit

Parameters:

	_bfu	The bit field unpacking context
	_wrds	The source word array
	_position	The bit position of the left most bit of the field to be extracted in the source array

#define _bfu_extract32	(	_bfu,
		_wrds,
		_position	)

Value:

(_bfu       = BFU__word (_wrds, _bfu.cur, _position),               \
        _position += 32,                                                   \
        _bfu.val)

Extracts 32 bits from the current position.

Returns:: The extract value

Parameters:

	_bfu	The bit field unpacking context
	_wrds	The source word array
	_position	The bit position of the left most bit of the field to be extracted in the source array

#define _bfu_extractBL	(	_bfu,
		_wrds,
		_position	)

Value:

(_bfu       = BFU__bitL (_wrds, _bfu.cur, _position),               \
        _position += 1,                                                    \
        _bfu.val)

Extracts the left justified bit from the current position.

Returns:: The left justified bit

Parameters:

	_bfu	The bit field unpacking context
	_wrds	The source word array
	_position	The bit position of the bit to be extracted from the source array

#define _bfu_extractBoolean	(	_bfu,
		_wrds,
		_position	)

Value:

(_bfu       = BFU__boolean (_wrds, _bfu.cur, _position),            \
        _position += 1,                                                    \
        _bfu.val)

Extracts the next bit, returning it as a boolean value. The justification is unspecfied. The implementation is the most efficient of _bfu_extractBL or _bfu_extractBR. Use one of those routine if the justification needs to be specified.

Return values:

	0,if	the bit was 0
	!=0,if	the bit was 1

Parameters:

	_bfu	The bit field unpacking context
	_wrds	The source word array
	_position	The bit position of the bit to be extracted from the source array

#define _bfu_extractBR	(	_bfu,
		_wrds,
		_position	)

Value:

(_bfu       = BFU__bitR (_wrds, _bfu.cur, _position),               \
        _position += 1,                                                    \
        _bfu.val)

Extracts the right justified bit from the current position.

Returns:: The right justified bit

Parameters:

	_bfu	The bit field unpacking context
	_wrds	The source word array
	_position	The bit position of the bit to be extracted from the source array

#define _bfu_extractL	(	_bfu,
		_wrds,
		_position,
		_width	)

Value:

(_bfu       = BFU__wordL (_wrds, _bfu.cur, _position, _width),     \
        _position += _width,                                              \
        _bfu.val)

Extracts a left justified value from the current position.

Returns:: The left justified value

Parameters:

	_bfu	The bit field unpacking context
	_wrds	The source word array
	_position	The bit position of the left most bit of the field to be extracted in the source array
	_width	The width of the field to be extracted; must be < 32

#define _bfu_extractR	(	_bfu,
		_wrds,
		_position,
		_width	)

Value:

(_bfu       = BFU__wordR (_wrds, _bfu.cur, _position, _width),     \
        _position += _width,                                              \
        _bfu.val)

Extracts a right justified value from the current position.

Returns:: The right justified value

Parameters:

	_bfu	The bit field unpacking context
	_wrds	The source word array
	_position	The bit position of the left most bit of the field to be extracted in the source array
	_width	The width of the field to be extracted; must be < 32

#define _bfu_get	(	_bfu,
		_tmp,
		_pos	)

Value:

_tmp = _bfu.cur;           \
                      _pos = _bfu.val;

Gets the current temporary buffer and buffer bit position.

Parameters:

	_bfu	The context to fetch the temporary buffer from
	_tmp	Returned as the value of the temporary holding buffer
	_pos	Returned as the value of the buffer bit position

#define _bfu_get_pos ( _bfu ) _bfu.val

Gets the current buffer bit position.

Return values:

The

value of the current buffer bit position

Parameters:

_bfu

The context to fetch the buffer bit position from

#define _bfu_get_tmp ( _bfu ) _bfu.cur

Gets the current temporary buffer.

Return values:

The

value of the temporary buffer

Parameters:

_bfu

The context to fetch the temporary buffer from

#define _bfu_put	(	_bfu,
		_tmp,
		_pos	)

Value:

_bfu.cur = _tmp;           \
                                       _bfu.val = _pos;

Updates the current temporary buffer and buffer bit position.

Parameters:

	_bfu	The context to update
	_tmp	The updated value of the temporary holding buffer
	_pos	The updated value of the buffer bit position

#define _bfu_put_pos	(	_bfu,
		_pos		)	_bfu.val = _pos;

Gets the current buffer bit position.

Parameters:

	_bfu	The context to fetch the buffer bit position from
	_pos	The updated value of the buffer bit position

#define _bfu_put_tmp	(	_bfu,
		_tmp		)	_bfu.cur = _tmp;

Updates the current temporary buffer.

Parameters:

	_bfu	The context to fetch the temporary buffer from
	_tmp	Returned as the updated value of the temporary holding buffer

#define _bfu_revert	(	_bfu,
		_wrds,
		_position,
		_nwidth,
		_nexp	)

Value:

({                                                                         \
   int  val;                                                               \
   int  exp        = _bfu_extractR (_bfu, _wrds, _position, _nexp) - 1;    \
   int  nleading   = (1 << _nexp) - 1;                                    \
   int  ntrailing  = (_nwidth - nleading > 0) ? _nwidth - nleading : 0;    \
   int  nbits      = (exp >= 0)                                            \
                   ? (exp += ntrailing, val = (1 << exp), exp)             \
                   : (val = 0, exp = ntrailing);                           \
                                                                           \
   /* printf ("Exp = %2u, Nbits = %2u\n", exp, nbits); */                  \
                                                                           \
   /* If any more bits, get them */                                        \
   if (nbits > 0)                                                          \
   {                                                                       \
      /* printf ("Val = %8.8x -> ", val); */                               \
      val |= _bfu_extractR (_bfu, _wrds, _position, nbits);                \
      /* printf ("%8.8x\n", val); */                                       \
   }                                                                       \
   val;                                                                    \
})

Counts the number of 1s till the first clear bit.

Returns:: The number of bits to the first clear bit

Parameters:

	_bfu	The bit field unpacking context
	_wrds	The source word array
	_position	The bit position of the left most bit of the field to be extracted in the source array
	_nwidth	The bit width of the word to be reverted
	_nexp	The number bits used to store the exponent

Warning:: This macro uses a GCC enhancement to the preprocessor and is likely not portable.

Function Documentation

static __inline BFU BFU__bitL	(	const unsigned int *	wrds,
		unsigned int	cur,
		unsigned int	position
	)			`[static]`

Unpacks the left justified bit from the current position.

Returns:: The extracted bit, right justified

Parameters:

	wrds	The input word array
	cur	The current set of bits one is working on
	position	The current bit position in the output bit field

static __inline BFU BFU__bitR	(	const unsigned int *	wrds,
		unsigned int	cur,
		unsigned int	position
	)			`[static]`

Unpacks the right justified bit from the current position.

Returns:: The extracted bit, right justified

Parameters:

	wrds	The input word array
	cur	The current set of bits one is working on
	position	The current bit position in the output bit field

static __inline BFU BFU__boolean	(	const unsigned int *	wrds,
		unsigned int	cur,
		unsigned int	position
	)			`[static]`

Unpacks the next bit. This is equivalent to a bit extract, but the justification (left or right) is unspecified. Rather the must efficient extraction is used, returning only 0 or non-zero. Use BFU__bitL or BFU__bitR if a specific justification is needed.

Return values:

	0,if	bit was 0
	!=0,if	bit was 1 (i.e. non-zero

Parameters:

	wrds	The input word array
	cur	The current set of bits one is working on
	position	The current bit position in the output bit field

static __inline BFU BFU__ffc	(	const unsigned int *	wrds,
		unsigned int	cur,
		unsigned int	position
	)			`[static]`

Scans the input bit stream for the first clear bit, this effectively counts the number of set bits.

Returns:: The updated BFU past the first clear bit.

Parameters:

	wrds	The input word array
	cur	The current 32-bit word
	position	The current bit position in the output bit field

static __inline BFU BFU__word	(	const unsigned int *	wrds,
		unsigned int	cur,
		unsigned int	position
	)			`[static]`

Unpacks exactly 32 bits from the current position.

Returns:: The extracted field, right justified

Parameters:

	wrds	The input word array
	cur	The current set of bits one is working on
	position	The current bit position in the output bit field

static __inline BFU BFU__wordL	(	const unsigned int *	wrds,
		unsigned int	cur,
		unsigned int	position,
		unsigned int	width
	)			`[static]`

Unpacks a left justified bit field from the current position. The width of the bit field must be less than 32 bits.

Returns:: The extracted field, left justified + the current buffered word

Parameters:

	wrds	The input word array
	cur	The current set of bits one is working on
	position	The current bit position in the output bit field
	width	The width of the field to be extracted

static __inline BFU BFU__wordR	(	const unsigned int *	wrds,
		unsigned int	cur,
		unsigned int	position,
		unsigned int	width
	)			`[static]`

Unpacks a right justified bit field from the current position. The width of the bit field must be less than 32 bits.

Returns:: The extracted field, right justified

Parameters:

	wrds	The input word array
	cur	The current set of bits one is working on
	position	The current bit position in the output bit field
	width	The width of the field to be extracted

Generated on Fri Jun 19 01:48:05 2009 by

1.5.3

BFU.h File Reference

Classes

Defines

Typedefs

Functions

Detailed Description

Define Documentation

Function Documentation