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more improvements to makemeta's piece size heuristics (SoftwareElves & charles_)

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This commit is contained in:
Charles Kerr 2007-06-19 16:36:15 +00:00
parent d4e1c19e32
commit bda9067ee7
1 changed files with 14 additions and 20 deletions
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34
libtransmission/makemeta.c
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@ -74,38 +74,32 @@ getFiles( const char * dir,
}
static int
bestPieceSize( uint64_t totalSize, uint64_t fileCount )
bestPieceSize( uint64_t totalSize, int fileCount )
{
int pieceSize = 1;
const int minPieceSize = 65536; /* arbitrary; 2^16 */
const int maxPieceSize = 16777216; /* arbitrary; 2^24 */
const int desiredMinPiecesPerFile = 15; /* arbitrary */
uint64_t log;
const int desiredMinPiecesPerFile = 10; /* arbitrary */
const unsigned int desiredPieces = fileCount * desiredMinPiecesPerFile;
/* start off in the range of (1024..2048] pieces
for "normal" torrents... */
log = totalSize;
/* a good starting range is to have (1024..2048] pieces... */
int pieceSize = 1;
uint64_t log = totalSize;
while( log > 2048 ) {
log >>= 1;
pieceSize <<= 1;
}
/* special case 1: torrents with a lot of small files.
try to have a reasonable number of pieces per file,
which will reduce overhead on selective downloading
/* now try to have N pieces per average file size...
this will reduce overhead on selective downloading
and increase swarm speed. */
while( totalSize/pieceSize < (fileCount * desiredMinPiecesPerFile) ) {
const int swap = pieceSize >> 1;
if( swap < minPieceSize )
break;
pieceSize = swap;
}
/* special case 2: enormous single-file torrents. our normal
case creates unwieldly piece sizes in that case */
while( pieceSize < maxPieceSize )
while( ( totalSize / pieceSize ) < desiredPieces )
pieceSize >>= 1;
/* clamp to our desired range to make sure we
haven't gone too far astray... */
if( pieceSize < minPieceSize ) pieceSize = minPieceSize;
if( pieceSize > maxPieceSize ) pieceSize = maxPieceSize;
return pieceSize;
}