size_t VSICachedFile::Read( void * pBuffer, size_t nSize, size_t nCount )
{
if( nOffset >= nFileSize )
return 0;
/* ==================================================================== */
/* Make sure the cache is loaded for the whole request region. */
/* ==================================================================== */
size_t nStartBlock = (size_t) (nOffset / CHUNK_SIZE);
size_t nEndBlock = (size_t) ((nOffset + nSize * nCount - 1) / CHUNK_SIZE);
for( size_t iBlock = nStartBlock; iBlock <= nEndBlock; iBlock++ )
{
if( apoCache.size() <= iBlock || apoCache[iBlock] == NULL )
{
size_t nBlocksToLoad = 1;
while( iBlock + nBlocksToLoad <= nEndBlock
&& (apoCache.size() <= iBlock+nBlocksToLoad
|| apoCache[iBlock+nBlocksToLoad] == NULL) )
nBlocksToLoad++;
LoadBlocks( iBlock, nBlocksToLoad, pBuffer, nSize * nCount );
}
}
/* ==================================================================== */
/* Copy data into the target buffer to the extent possible. */
/* ==================================================================== */
size_t nAmountCopied = 0;
while( nAmountCopied < nSize * nCount )
{
size_t iBlock = (size_t) ((nOffset + nAmountCopied) / CHUNK_SIZE);
size_t nThisCopy;
VSICacheChunk *poBlock = apoCache[iBlock];
nThisCopy = (size_t)
((iBlock * CHUNK_SIZE + poBlock->nDataFilled)
- nAmountCopied - nOffset);
if( nThisCopy > nSize * nCount - nAmountCopied )
nThisCopy = nSize * nCount - nAmountCopied;
if( nThisCopy == 0 )
break;
memcpy( ((GByte *) pBuffer) + nAmountCopied,
poBlock->abyData
+ (nOffset + nAmountCopied) - iBlock * CHUNK_SIZE,
nThisCopy );
nAmountCopied += nThisCopy;
}
nOffset += nAmountCopied;
/* -------------------------------------------------------------------- */
/* Ensure the cache is reduced to our limit. */
/* -------------------------------------------------------------------- */
while( nCacheUsed > nCacheMax )
FlushLRU();
return nAmountCopied / nSize;
}
size_t VSICachedFile::Read( void * pBuffer, size_t nSize, size_t nCount )
{
if( nOffset >= nFileSize )
{
bEOF = TRUE;
return 0;
}
/* ==================================================================== */
/* Make sure the cache is loaded for the whole request region. */
/* ==================================================================== */
vsi_l_offset nStartBlock = nOffset / nChunkSize;
vsi_l_offset nEndBlock = (nOffset + nSize * nCount - 1) / nChunkSize;
for( vsi_l_offset iBlock = nStartBlock; iBlock <= nEndBlock; iBlock++ )
{
if( apoCache.size() <= iBlock || apoCache[iBlock] == NULL )
{
size_t nBlocksToLoad = 1;
while( iBlock + nBlocksToLoad <= nEndBlock
&& (apoCache.size() <= iBlock+nBlocksToLoad
|| apoCache[iBlock+nBlocksToLoad] == NULL) )
nBlocksToLoad++;
LoadBlocks( iBlock, nBlocksToLoad, pBuffer, nSize * nCount );
}
}
/* ==================================================================== */
/* Copy data into the target buffer to the extent possible. */
/* ==================================================================== */
size_t nAmountCopied = 0;
while( nAmountCopied < nSize * nCount )
{
vsi_l_offset iBlock = (nOffset + nAmountCopied) / nChunkSize;
size_t nThisCopy;
VSICacheChunk *poBlock = apoCache[iBlock];
if( poBlock == NULL )
{
/* We can reach that point when the amount to read exceeds */
/* the cache size */
LoadBlocks( iBlock, 1, ((GByte *) pBuffer) + nAmountCopied,
MIN(nSize * nCount - nAmountCopied, nChunkSize) );
poBlock = apoCache[iBlock];
CPLAssert(poBlock != NULL);
}
vsi_l_offset nStartOffset = (vsi_l_offset)iBlock * nChunkSize;
nThisCopy = (size_t)
((nStartOffset + poBlock->nDataFilled)
- nAmountCopied - nOffset);
if( nThisCopy > nSize * nCount - nAmountCopied )
nThisCopy = nSize * nCount - nAmountCopied;
if( nThisCopy == 0 )
break;
memcpy( ((GByte *) pBuffer) + nAmountCopied,
poBlock->pabyData
+ (nOffset + nAmountCopied) - nStartOffset,
nThisCopy );
nAmountCopied += nThisCopy;
}
nOffset += nAmountCopied;
/* -------------------------------------------------------------------- */
/* Ensure the cache is reduced to our limit. */
/* -------------------------------------------------------------------- */
while( nCacheUsed > nCacheMax )
FlushLRU();
size_t nRet = nAmountCopied / nSize;
if (nRet != nCount)
bEOF = TRUE;
return nRet;
}