Conjecture::BitOverlay Class Reference

#include <BitOverlay.h>

Inheritance diagram for Conjecture::BitOverlay:

List of all members.

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Detailed Description

Hyper-low-level bit analysis.

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This class provides a variety of routines for analyzing the bits within a 32-bit value.

There are both static and instance versions of each method.

An "on" bit is 1, an "off" bit is 0.

IMPORTANT: This class can be used as simply a collection of static methods, OR it can be used as an "overlay", a means of adding semantics and functionality to an arbitrary integer. However, in order for it to be an overlay, NO VIRTUAL METHODS! We do not want a vtbl here! Includes parents, of course. Because of this, statically typing a variable as BitOverlay and assigning it an instance of the subclass BitInfo is NOT recommended.

FUTURE WORK: Analyze http://graphics.stanford.edu/~seander/bithacks.html and incorporate useful methods from there into this class!

See Also: BitOverlay64

Public Types
typedef unsigned int	Layout
typedef int	BitPos
typedef unsigned	BitCount
Public Member Functions
	BitOverlay (Layout data)
Layout	bits () const
BitPos	findFirstHigh () const
BitPos	findFirstLow () const
BitCount	popc () const
std::string	str () const
BitCount	regions (int *largest=NULL, int *all=NULL) const
Static Public Member Functions
static BitPos	FindFirstHigh (Layout val)
static BitPos	FindFirstHighSlow (Layout val)
static BitPos	FindFirstLow (Layout val)
static int	_bx (Layout x)
static BitCount	PopCount (Layout val)
static BitCount	PopCountSlow (Layout val)
static std::string	Str (Layout val)
static BitCount	Regions (Layout val, int *largest=NULL, int *all=NULL)
static void	Test (int argc=0, const char *argv[]=NULL)
Static Public Attributes
static const BitPos	npos = 255
Protected Member Functions
void	bitsIs (const Layout &bits)

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Member Typedef Documentation

typedef unsigned Conjecture::BitOverlay::BitCount

A type for use in methods that return a bit count.

typedef int Conjecture::BitOverlay::BitPos

A bit position. Bit position 0 is the lowest-order bit, and bit position 31 is the highest-order-bit. The special value 'npos' is used to represent "not present", and is outside the 0-31 range. NOTE: Although this type could be described using a single byte (the maximum bit position possible is 31, after all), it is defined as an 'int' because 'char' types get printed out as chars, not integers, when used in '<<' debugging operators. If size becomes relevant, it can be changed to 'unsigned char'. FUTURE FIX: A better name for this type should be found!

typedef unsigned int Conjecture::BitOverlay::Layout

The type describing the underlying value being analyzed. A typedef to make a BitOverlay64 implementation look as similar as possible to BitOverlay (and to make potential transitioning to a template implementation easier).

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Member Function Documentation

static int Conjecture::BitOverlay::_bx (  Layout  x  )  [inline, static]

Population Count: Returns the number of "on" bits.

BitOverlay::BitPos Conjecture::BitOverlay::FindFirstHigh (  Layout  val  )  [static]

Returns the bit position of the most-significant "on" bit. NOTE: Some chipsets have a 'find-first-set' (ffs) instruction that implements this. I've renamed it because I want to distinguish ffh and ffl.

BitOverlay::BitPos Conjecture::BitOverlay::FindFirstLow (  Layout  val  )  [static]

Returns the bit position of the least-significant "on" bit.

BitOverlay::BitCount Conjecture::BitOverlay::Regions (  Layout  val, int *  largest = NULL, int *  all = NULL )  [static]

Returns number of "regions" of contiguous "on" pixels. Parameters: val  The sequence of bits to analyze largest  If non-null, it is assigned the length of the largest region. all  If non-null, a pre-allocated array of size 16+, into which the sizes of each region are placed (may also encode start-bit-position).

string Conjecture::BitOverlay::Str (  Layout  val  )  [static]

String representation of 'val' as a binary number. Currently always returns a string of length 32. Future extensions may add an optional arg specifying when we can truncate (could use FFS to establish minimum length).

void Conjecture::BitOverlay::Test (  int  argc = 0, const char *  argv[] = NULL )  [static]

The Unit-testing method Reimplemented in Conjecture::BitInfo.

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The documentation for this class was generated from the following files:

• BitOverlay.h
• BitOverlay.cc

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