barrier/lib/io/CStreamBuffer.cpp

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#include "CStreamBuffer.h"
//
// CStreamBuffer
//
const UInt32 CStreamBuffer::kChunkSize = 4096;
CStreamBuffer::CStreamBuffer() :
m_size(0),
m_headUsed(0)
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{
// do nothing
}
CStreamBuffer::~CStreamBuffer()
{
// do nothing
}
const void*
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CStreamBuffer::peek(UInt32 n)
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{
assert(n <= m_size);
// reserve space in first chunk
ChunkList::iterator head = m_chunks.begin();
head->reserve(n + m_headUsed);
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// consolidate chunks into the first chunk until it has n bytes
ChunkList::iterator scan = head;
++scan;
while (head->size() - m_headUsed < n && scan != m_chunks.end()) {
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head->insert(head->end(), scan->begin(), scan->end());
scan = m_chunks.erase(scan);
}
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return reinterpret_cast<const void*>(&(head->begin()[m_headUsed]));
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}
void
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CStreamBuffer::pop(UInt32 n)
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{
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// discard all chunks if n is greater than or equal to m_size
if (n >= m_size) {
m_size = 0;
m_headUsed = 0;
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m_chunks.clear();
return;
}
// update size
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m_size -= n;
// discard chunks until more than n bytes would've been discarded
ChunkList::iterator scan = m_chunks.begin();
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assert(scan != m_chunks.end());
while (scan->size() - m_headUsed <= n) {
n -= scan->size() - m_headUsed;
m_headUsed = 0;
scan = m_chunks.erase(scan);
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assert(scan != m_chunks.end());
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}
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// remove left over bytes from the head chunk
if (n > 0) {
m_headUsed += n;
}
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}
void
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CStreamBuffer::write(const void* vdata, UInt32 n)
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{
assert(vdata != NULL);
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// ignore if no data, otherwise update size
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if (n == 0) {
return;
}
m_size += n;
// cast data to bytes
const UInt8* data = reinterpret_cast<const UInt8*>(vdata);
// point to last chunk if it has space, otherwise append an empty chunk
ChunkList::iterator scan = m_chunks.end();
if (scan != m_chunks.begin()) {
--scan;
if (scan->size() >= kChunkSize) {
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++scan;
}
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}
if (scan == m_chunks.end()) {
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scan = m_chunks.insert(scan, Chunk());
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}
// append data in chunks
while (n > 0) {
// choose number of bytes for next chunk
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assert(scan->size() <= kChunkSize);
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UInt32 count = kChunkSize - scan->size();
if (count > n)
count = n;
// transfer data
scan->insert(scan->end(), data, data + count);
n -= count;
data += count;
// append another empty chunk if we're not done yet
if (n > 0) {
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++scan;
scan = m_chunks.insert(scan, Chunk());
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}
}
}
UInt32
CStreamBuffer::getSize() const
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{
return m_size;
}