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Remove an erroneous 0.5 in compute_weighted_bandwidths()

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Back in 0.2.4.3-alpha (e106812a77), when we switched from using
double to using uint64 for selecting by bandwidth, I got the math
wrong: I should have used llround(x), or (uint64_t)(x+0.5), but
instead I wrote llround(x+0.5).  That means we would always round
up, rather than rounding to the closest integer

Fixes bug 23318; bugfix on 0.2.4.3-alpha.
This commit is contained in:
Nick Mathewson 2017-09-22 15:29:15 -04:00
parent 04d4786cc4
commit 3c03e237ab
2 changed files with 8 additions and 1 deletions
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7
changes/bug23318 Normal file
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@ -0,0 +1,7 @@
o Minor bugfixes (path selection):
- When selecting relays by bandwidth, avoid a rounding error that
could sometimes cause load to be imbalanced incorrectly. Previously,
we would always round upwards; now, we round towards the nearest
integer. This had the biggest effect when a relay's weight adjustments
should have given it weight 0, but it got weight 1 instead.
Fixes bug 23318; bugfix on 0.2.4.3-alpha.

2
src/or/routerlist.c
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@ -2713,7 +2713,7 @@ compute_weighted_bandwidths(const smartlist_t *sl,
final_weight = weight*this_bw; final_weight = weight*this_bw;
} }
bandwidths[node_sl_idx] = final_weight + 0.5; bandwidths[node_sl_idx] = final_weight;
} SMARTLIST_FOREACH_END(node); } SMARTLIST_FOREACH_END(node);
log_debug(LD_CIRC, "Generated weighted bandwidths for rule %s based " log_debug(LD_CIRC, "Generated weighted bandwidths for rule %s based "