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authorGerrit Renker <gerrit@erg.abdn.ac.uk>2008-06-11 11:19:10 +0100
committerGerrit Renker <gerrit@erg.abdn.ac.uk>2008-06-11 11:19:10 +0100
commit1e8a287c79f64226541f5c44aa52d4698bb84cf5 (patch)
treea280516dae548981cd9c9f981cc7bd8ec879baf2
parent65907a433ac0ca450c4408080f24c6e4743386b2 (diff)
dccp ccid-3: TFRC reverse-lookup Bug-Fix
This fixes a bug in the reverse lookup of p: given a value f(p), instead of p, the function returned the smallest tabulated value f(p). The smallest tabulated value of 10^6 * f(p) = sqrt(2*p/3) + 12 * sqrt(3*p/8) * (32 * p^3 + p) for p=0.0001 is 8172. Since this value is scaled by 10^6, the outcome of this bug is that a loss of 8172/10^6 = 0.8172% was reported whenever the input was below the table resolution of 0.01%. This means that the value was over 80 times too high, resulting in large spikes of the initial loss interval, thus unnecessarily reducing the throughput. Also corrected the printk format (%u for u32). Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
-rw-r--r--net/dccp/ccids/lib/tfrc_equation.c8
1 files changed, 4 insertions, 4 deletions
diff --git a/net/dccp/ccids/lib/tfrc_equation.c b/net/dccp/ccids/lib/tfrc_equation.c
index e4e64b76c10..2f20a29cffe 100644
--- a/net/dccp/ccids/lib/tfrc_equation.c
+++ b/net/dccp/ccids/lib/tfrc_equation.c
@@ -661,7 +661,7 @@ u32 tfrc_calc_x(u16 s, u32 R, u32 p)
EXPORT_SYMBOL_GPL(tfrc_calc_x);
-/*
+/**
* tfrc_calc_x_reverse_lookup - try to find p given f(p)
*
* @fvalue: function value to match, scaled by 1000000
@@ -676,11 +676,11 @@ u32 tfrc_calc_x_reverse_lookup(u32 fvalue)
/* Error cases. */
if (fvalue < tfrc_calc_x_lookup[0][1]) {
- DCCP_WARN("fvalue %d smaller than resolution\n", fvalue);
- return tfrc_calc_x_lookup[0][1];
+ DCCP_WARN("fvalue %u smaller than resolution\n", fvalue);
+ return TFRC_SMALLEST_P;
}
if (fvalue > tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][0]) {
- DCCP_WARN("fvalue %d exceeds bounds!\n", fvalue);
+ DCCP_WARN("fvalue %u exceeds bounds!\n", fvalue);
return 1000000;
}