New, fixpoint distinct random algorithm for choosing peers from the list... may contain bugs. Feedback welcome

master
Dirk Engling 16 years ago
parent 1e706713cc
commit 134779877b
  1. 42
      trackerlogic.c

@ -229,7 +229,6 @@ ot_torrent *add_peer_to_torrent( ot_hash *hash, ot_peer *peer ) {
size_t return_peers_for_torrent( ot_torrent *torrent, unsigned int amount, char *reply ) {
char *r = reply;
unsigned int peer_count, seed_count, index;
int pool_offset = -1, pool_index = 0, wert = -1;
#ifdef WANT_CLOSED_TRACKER
if( torrent == OT_TORRENT_NOT_ON_WHITELIST ) {
@ -254,19 +253,36 @@ size_t return_peers_for_torrent( ot_torrent *torrent, unsigned int amount, char
if( peer_count < amount ) amount = peer_count;
r += sprintf( r, "d8:completei%ie10:incompletei%ie8:intervali600e5:peers%i:", seed_count, peer_count-seed_count, 6*amount );
for( index = 0; index < amount; ++index ) {
double step = 1.8*((double)( peer_count - wert - 1 ))/((double)( amount - index ));
int off = random() % (int)step;
off = 1 + ( off % ( peer_count - wert - 1 ));
wert += off; pool_offset += off;
while( pool_offset >= torrent->peer_list->peers[pool_index].size ) {
pool_offset -= torrent->peer_list->peers[pool_index].size;
pool_index++;
}
if( amount ) {
unsigned int pool_offset, pool_index = 0;;
unsigned int shifted_pc = peer_count;
unsigned int shifted_step = 0;
unsigned int shift = 0;
/* Make fixpoint arithmetic as exact as possible */
#define MAXPRECBIT (1<<(8*sizeof(int)-3))
while( !(shifted_pc & MAXPRECBIT ) ) { shifted_pc <<= 1; shift++; }
shifted_step = shifted_pc/amount;
#undef MAXPRECBIT
/* Initialize somewhere in the middle of peers so that
fixpoint's aliasing doesn't alway miss the same peers */
pool_offset = random() % peer_count;
for( index = 0; index < amount; ++index ) {
/* This is the aliased, non shifted range, next value may fall into */
unsigned int diff = ( ( ( index + 1 ) * shifted_step ) >> shift ) -
( ( index * shifted_step ) >> shift );
pool_offset += 1 + random() % diff;
while( pool_offset >= torrent->peer_list->peers[pool_index].size ) {
pool_offset -= torrent->peer_list->peers[pool_index].size;
pool_index = ( pool_index + 1 ) % OT_POOLS_COUNT;
}
memmove( r, ((ot_peer*)torrent->peer_list->peers[pool_index].data) + pool_offset, 6 );
r += 6;
memmove( r, ((ot_peer*)torrent->peer_list->peers[pool_index].data) + pool_offset, 6 );
r += 6;
}
}
*r++ = 'e';

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