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Merge pull request #6718

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85efc88c1 Fix overflow issue in epee:misc_utils::rolling_median_t and median(), with unit test (koe)
This commit is contained in:
Alexander Blair 2020-08-16 12:53:50 -07:00
commit 10ad0d7eb2
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3 changed files with 23 additions and 2 deletions
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10
contrib/epee/include/misc_language.h
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@ -106,6 +106,14 @@ namespace misc_utils
return true;
}
template <typename T>
T get_mid(const T &a, const T &b)
{
//returns the average of two numbers; overflow safe and works with at least all integral and floating point types
//(a+b)/2 = (a/2) + (b/2) + ((a - 2*(a/2)) + (b - 2*(b/2)))/2
return (a/2) + (b/2) + ((a - 2*(a/2)) + (b - 2*(b/2)))/2;
}
template<class type_vec_type>
type_vec_type median(std::vector<type_vec_type> &v)
{
@ -122,7 +130,7 @@ namespace misc_utils
return v[n];
}else
{//2, 4, 6...
return (v[n-1] + v[n])/2;
return get_mid<type_vec_type>(v[n-1],v[n]);
}
}

4
contrib/epee/include/rolling_median.h
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@ -34,6 +34,8 @@
#pragma once
#include "misc_language.h"
#include <stdlib.h>
#include <stdint.h>
@ -226,7 +228,7 @@ public:
Item v = data[heap[0]];
if (minCt < maxCt)
{
v = (v + data[heap[-1]]) / 2;
v = get_mid<Item>(v, data[heap[-1]]);
}
return v;
}

11
tests/unit_tests/rolling_median.cpp
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@ -170,6 +170,17 @@ TEST(rolling_median, history_blind)
}
}
TEST(rolling_median, overflow)
{
epee::misc_utils::rolling_median_t<uint64_t> m(2);
uint64_t over_half = static_cast<uint64_t>(3) << static_cast<uint64_t>(62);
m.insert(over_half);
m.insert(over_half);
ASSERT_EQ((over_half + over_half) < over_half, true);
ASSERT_EQ(over_half, m.median());
}
TEST(rolling_median, size)
{
epee::misc_utils::rolling_median_t<uint64_t> m(10);