BIT.h File Reference

Utility routines to manipulate 16 and 32 bit words. More...

Defines
#define	BW_(x)
	Replaces each 4-bit sequence in arg by the number of bits in sequence.
#define	BS_(x)
	Replaces each 4-bit sequence in arg by the number of bits in sequence.
Functions
static __inline unsigned int	BIT__countW (unsigned int w)
	Computes the number of bits set (1) in 32-bit argument.
static __inline unsigned int	BIT__countS (unsigned short int s)
	Computes the number of bits set (1) in 16-bit argument.
static __inline unsigned int	BIT__countB (unsigned char c)
	Computes the number of bits set (1) in 8-bit argument.

---

Detailed Description

Utility routines to manipulate 16 and 32 bit words.

Author:

JJRussell - russell@slac.stanford.edu

   CVS $Id: BIT.h,v 1.2 2009/04/29 23:01:53 russell Exp $

---

Define Documentation

#define BS_

(

x

)

Value:

((x) - (((x)>>1)&0x7777)                        \
                               - (((x)>>2)&0x3333)                        \
                               - (((x)>>3)&0x1111))

Replaces each 4-bit sequence in arg by the number of bits in sequence.

See also:

BIT_countS

Replaces each 4-bit sequence in 16-bit argument by the number of bits in that sequence (which will, of course, fit in 4 bits).

Warning:

This is not a public macro, it used only to implement BIT32_count

Referenced by BIT__countS().

#define BW_

(

x

)

Value:

((x) - (((x)>>1)&0x77777777)                    \
                               - (((x)>>2)&0x33333333)                    \
                               - (((x)>>3)&0x11111111))

Replaces each 4-bit sequence in arg by the number of bits in sequence.

See also:

BIT_countW

Replaces each 4-bit sequence in 32-bit argument by the number of bits in that sequence (which will, of course, fit in 4 bits).

Warning:

This is not a public macro, it used only to implement BIT32_count

Referenced by BIT__countW().

---

Function Documentation

static __inline unsigned int BIT__countB

(

unsigned char

c

)

[static]

Computes the number of bits set (1) in 8-bit argument.

Returns:

The number of set bits

Parameters:

c

The character to count the bits in

The algorithm is to do this in two 4-bit chunks, where the nibbles are used to access an array of 16 x 2 bit values. 2* nibble-1 is used as an index the array. The array itself holds the count, except the value 0xf must be special cased, since the number of bits is 4, a value that is unable to fit into 2 bits.

static __inline unsigned int BIT__countS

(

unsigned short int

s

)

[static]

Computes the number of bits set (1) in 16-bit argument.

See also:

BS_

Credit to Chris Smith (original algorithm) Jane Huffman (original writer) Brad Merril & Jerry Leichter (ported from 36-bit words to 32-bit words)

References BS_.

static __inline unsigned int BIT__countW

(

unsigned int

w

)

[static]

Computes the number of bits set (1) in 32-bit argument.

See also:

BW_

Credit to Chris Smith (original algorithm) Jane Huffman (original writer) Brad Merril & Jerry Leichter (ported from 36-bit words to 32-bit words)

References BW_.