commit 052b95e2f196211c97b33ce8c68960e1c2561ea0 Author: Nick Mathewson nickm@torproject.org Date: Wed Sep 7 21:22:02 2011 -0400
Refactor connection_bucket_refill(_helper) to avoid roundoff
We were doing "divide bandwidth by 1000, then multiply by msec", but that would lose accuracy: instead of getting your full bandwidth, you'd lose up to 999 bytes per sec. (Not a big deal, but every byte helps.)
Instead, do the multiply first, then the division. This can easily overflow a 32-bit value, so make sure to do it as a 64-bit operation. --- src/or/connection.c | 16 ++++++++-------- 1 files changed, 8 insertions(+), 8 deletions(-)
diff --git a/src/or/connection.c b/src/or/connection.c index 42d7e2f..cb93a81 100644 --- a/src/or/connection.c +++ b/src/or/connection.c @@ -2389,7 +2389,7 @@ connection_bucket_init(void) }
/** Refill a single <b>bucket</b> called <b>name</b> with bandwidth rate - * per millisecond <b>rate</b> and bandwidth burst per refill interval + * per second <b>rate</b> and bandwidth burst per refill interval * <b>burst</b>, assuming that <b>milliseconds_elapsed</b> milliseconds * have passed since the last call. */ static void @@ -2398,13 +2398,13 @@ connection_bucket_refill_helper(int *bucket, int rate, int burst, const char *name) { int starting_bucket = *bucket; - if (starting_bucket < burst && milliseconds_elapsed) { - if (((burst - starting_bucket)/milliseconds_elapsed) < rate) { + if (starting_bucket < burst && milliseconds_elapsed > 0) { + int64_t incr = (((int64_t)rate) * milliseconds_elapsed) / 1000; + if ((burst - starting_bucket) < incr) { *bucket = burst; /* We would overflow the bucket; just set it to * the maximum. */ } else { - int incr = rate*milliseconds_elapsed; - *bucket += incr; + *bucket += (int)incr; if (*bucket > burst || *bucket < starting_bucket) { /* If we overflow the burst, or underflow our starting bucket, * cap the bucket value to burst. */ @@ -2425,11 +2425,11 @@ connection_bucket_refill(int milliseconds_elapsed, time_t now) smartlist_t *conns = get_connection_array(); int bandwidthrate, bandwidthburst, relayrate, relayburst;
- bandwidthrate = (int)options->BandwidthRate / 1000; + bandwidthrate = (int)options->BandwidthRate; bandwidthburst = (int)options->BandwidthBurst;
if (options->RelayBandwidthRate) { - relayrate = (int)options->RelayBandwidthRate / 1000; + relayrate = (int)options->RelayBandwidthRate; relayburst = (int)options->RelayBandwidthBurst; } else { relayrate = bandwidthrate; @@ -2464,7 +2464,7 @@ connection_bucket_refill(int milliseconds_elapsed, time_t now) { if (connection_speaks_cells(conn)) { or_connection_t *or_conn = TO_OR_CONN(conn); - int orbandwidthrate = or_conn->bandwidthrate / 1000; + int orbandwidthrate = or_conn->bandwidthrate; int orbandwidthburst = or_conn->bandwidthburst; if (connection_bucket_should_increase(or_conn->read_bucket, or_conn)) { connection_bucket_refill_helper(&or_conn->read_bucket,