ByteBuffer Class Reference

ByteBuffer allows access to an array of buffers as a single memory space. More...

#include <ByteBuffer.h>

List of all members.

Public Member Functions
	ByteBuffer ()
void	init (boost::shared_array< PBuffer > ppBuffers, uint nBuffers, uint bufSize)
	Provides storage for the virtual byte buffer.
uint	getSize ()
	Returns the size of the buffer, in bytes.
UnsignedByte	getByte (uint pos)
	Returns the byte at pos.
void	setByte (uint pos, UnsignedByte b)
	Sets byte at pos.
void	mergeByte (uint pos, UnsignedByte b)
	Merges (OR's) byte at pos.
PBuffer	getMem (uint pos, uint &size)
	Returns a pointer to contiguous memory.
void	setMem (uint pos, UnsignedByte value, uint len)
	Initializes a run of bytes in the buffer.
void	copyMem (uint pos, PConstBuffer mem, uint len)
	Copies a run of bytes into the buffer.
void	mergeMem (uint pos, PConstBuffer mem, uint len)
	Merges (OR's) a run of bytes into the buffer; similar to memmerge.
Private Member Functions
uint	getI (uint pos)
	Returns which buffer to use to access pos.
uint	getJ (uint pos)
	Returns offset within buffer to use to access pos.
Static Private Member Functions
static void	memmerge (PBuffer dest, PConstBuffer src, uint len)
	Merges (OR's) one buffer into another.
Private Attributes
boost::shared_array< PBuffer >	ppBuffers
uint	nBuffers
uint	bufferSize
uint	bufferMask
uint	bufferShift

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Detailed Description

ByteBuffer allows access to an array of buffers as a single memory space.

It allows for optimization with direct memory access. It has an interface for accessing one byte at a time (less overhead), and an interface for accessing runs of bytes (more overhead, but processes one memory chunk at a time). The methods setMem and copyMem are similar to memset and memcpy.

This class neither allocates nor deallocates memory, except through shared pointers. As usual, indexes are zero-based.

Author:

John Pham

Version:

Id

//open/dev/fennel/common/ByteBuffer.h#9

Definition at line 48 of file ByteBuffer.h.

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Constructor & Destructor Documentation

ByteBuffer::ByteBuffer

(

)

[explicit]

Definition at line 27 of file ByteBuffer.cpp.

References bufferSize, and nBuffers.

{
    nBuffers = 0;
    bufferSize = 0;
}

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Member Function Documentation

uint ByteBuffer::getI

(

uint

pos

)

[inline, private]

Returns which buffer to use to access pos.

Definition at line 59 of file ByteBuffer.h.

    {
        uint i = pos >> bufferShift;
        assert(i < nBuffers);
        return i;
    }

uint ByteBuffer::getJ

(

uint

pos

)

[inline, private]

Returns offset within buffer to use to access pos.

Definition at line 69 of file ByteBuffer.h.

    {
        uint j = pos & bufferMask;
        assert(j < bufferSize);
        return j;
    }

static void ByteBuffer::memmerge	(	PBuffer	dest,
		PConstBuffer	src,
		uint	len
	)			[inline, static, private]

Merges (OR's) one buffer into another.

Definition at line 79 of file ByteBuffer.h.

Referenced by mergeMem().

    {
        PBuffer end = dest + len;
        while (dest < end) {
            *dest++ |= *src++;
        }
    }

void ByteBuffer::init	(	boost::shared_array< PBuffer >	ppBuffers,
		uint	nBuffers,
		uint	bufSize
	)

Provides storage for the virtual byte buffer.

Definition at line 33 of file ByteBuffer.cpp.

References bufferMask, bufferShift, and bufferSize.

Referenced by LbmUnionExecStream::open().

{
    this->ppBuffers = ppBuffers;
    this->nBuffers = nBuffers;
    this->bufferSize = bufSize;

    // Currently we use bit masking (rather than mod) to calculate virtual
    // offsets. This scheme requires that the buffer size be a power of 2.
    // If this cannot be guaranteed, we should change to another scheme.
    bufferMask = bufSize - 1;
    assert((bufferMask & bufSize) == 0);

    bufferShift = 0;
    uint tmp = bufferMask;
    while (tmp > 0) {
        bufferShift++;
        tmp >>=1;
    }
}

uint ByteBuffer::getSize

(

)

Returns the size of the buffer, in bytes.

Definition at line 54 of file ByteBuffer.cpp.

References bufferSize, and nBuffers.

Referenced by copyMem(), mergeMem(), and setMem().

{
    return nBuffers * bufferSize;
}

UnsignedByte ByteBuffer::getByte

(

uint

pos

)

[inline]

Returns the byte at pos.

Definition at line 104 of file ByteBuffer.h.

    {
        return ppBuffers[getI(pos)][getJ(pos)];
    }

void ByteBuffer::setByte	(	uint	pos,
		UnsignedByte	b
	)			[inline]

Sets byte at pos.

Definition at line 112 of file ByteBuffer.h.

    {
        ppBuffers[getI(pos)][getJ(pos)] = b;
    }

void ByteBuffer::mergeByte	(	uint	pos,
		UnsignedByte	b
	)			[inline]

Merges (OR's) byte at pos.

Definition at line 120 of file ByteBuffer.h.

    {
        ppBuffers[getI(pos)][getJ(pos)] |= b;
    }

PBuffer ByteBuffer::getMem	(	uint	pos,
		uint &	size
	)			[inline]

Returns a pointer to contiguous memory.

Parameters:

	pos	memory position
	size	returns size of the contiguous memory

Definition at line 131 of file ByteBuffer.h.

Referenced by copyMem(), mergeMem(), and setMem().

    {
        size = bufferSize - getJ(pos);
        return &ppBuffers[getI(pos)][getJ(pos)];
    }

void ByteBuffer::setMem	(	uint	pos,
		UnsignedByte	value,
		uint	len
	)

Initializes a run of bytes in the buffer.

Definition at line 59 of file ByteBuffer.cpp.

References getMem(), and getSize().

{
    assert(pos + len <= getSize());
    uint current = pos;
    uint remaining = len;

    while (remaining > 0) {
        uint chunkLen;
        PBuffer mem = getMem(current, chunkLen);
        if (chunkLen >= remaining) {
            memset(mem, value, remaining);
            break;
        }
        memset(mem, value, chunkLen);
        current += chunkLen;
        remaining -= chunkLen;
    }
}

void ByteBuffer::copyMem	(	uint	pos,
		PConstBuffer	mem,
		uint	len
	)

Copies a run of bytes into the buffer.

Definition at line 78 of file ByteBuffer.cpp.

References getMem(), and getSize().

{
    assert(pos + len <= getSize());
    uint current = pos;
    PConstBuffer currentData = data;
    uint remaining = len;

    while (remaining > 0) {
        uint chunkLen;
        PBuffer mem = getMem(current, chunkLen);
        if (chunkLen >= remaining) {
            memcpy(mem, currentData, remaining);
            break;
        }
        memcpy(mem, currentData, chunkLen);
        current += chunkLen;
        currentData += chunkLen;
        remaining -= chunkLen;
    }
}

void ByteBuffer::mergeMem	(	uint	pos,
		PConstBuffer	mem,
		uint	len
	)

Merges (OR's) a run of bytes into the buffer; similar to memmerge.

Definition at line 99 of file ByteBuffer.cpp.

References getMem(), getSize(), and memmerge().

{
    assert(pos + len <= getSize());
    uint current = pos;
    PConstBuffer currentData = data;
    uint remaining = len;

    while (remaining > 0) {
        uint chunkLen;
        PBuffer mem = getMem(current, chunkLen);
        if (chunkLen >= remaining) {
            memmerge(mem, currentData, remaining);
            break;
        }
        memmerge(mem, currentData, chunkLen);
        current += chunkLen;
        currentData += chunkLen;
        remaining -= chunkLen;
    }
}

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Member Data Documentation

boost::shared_array<PBuffer> ByteBuffer::ppBuffers [private]

Definition at line 50 of file ByteBuffer.h.

uint ByteBuffer::nBuffers [private]

Definition at line 51 of file ByteBuffer.h.

Referenced by ByteBuffer(), and getSize().

uint ByteBuffer::bufferSize [private]

Definition at line 52 of file ByteBuffer.h.

Referenced by ByteBuffer(), getSize(), and init().

uint ByteBuffer::bufferMask [private]

Definition at line 53 of file ByteBuffer.h.

Referenced by init().

uint ByteBuffer::bufferShift [private]

Definition at line 54 of file ByteBuffer.h.

Referenced by init().

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

• /home/pub/open/dev/fennel/common/ByteBuffer.h
• /home/pub/open/dev/fennel/common/ByteBuffer.cpp

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