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Adds a test showing how to get conflicts on CRC. #559

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Aug 11, 2021
Merged

Adds a test showing how to get conflicts on CRC. #559

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72 changes: 71 additions & 1 deletion src/utils/Crc.cxxtest
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Original file line number Diff line number Diff line change
@@ -1,7 +1,8 @@
#include "utils/Crc.hxx"

#include <stdlib.h>
#include "utils/format_utils.hxx"
#include "utils/test_main.hxx"
#include <stdlib.h>

extern uint8_t reverse(uint8_t data);

Expand Down Expand Up @@ -105,3 +106,72 @@ TEST(Crc8Test, Fuzz)
EXPECT_EQ(c0.get(), c256.get());
}
}

string get_sample(unsigned suffix)
{
const uint8_t prefixbytes[] = {0, 0x99, 0x11, 0x22, 0x33};
string s((const char *)prefixbytes, 5);
s.push_back(suffix & 0xff);
s[4] ^= (suffix >> 8);
return s;
}

// Shows the collision behavior of CRC8.
TEST(Crc8Test, Collision)
{
std::map<uint8_t, unsigned> rev_lookup;
unsigned c1, c2;
for (unsigned i = 0; i < 2 * 256; i++)
{
string s = get_sample(i);
Crc8DallasMaxim m;
for (unsigned j = 0; j < 6; j++)
{
m.update256(s[j]);
}
uint8_t crc = m.get();
if (rev_lookup.find(crc) != rev_lookup.end())
{
c1 = i;
c2 = rev_lookup[crc];
LOG(INFO, "collision: %d %d on %02x", c1, c2, crc);
break;
}
rev_lookup[crc] = i;
}
string s1 = get_sample(c1), s2 = get_sample(c2);
Crc8DallasMaxim m1, m2;
for (unsigned i = 0; i < 6; i++)
{
m1.update256(s1[i]);
m2.update256(s2[i]);
}
LOG(INFO, "1 %02x %02x %d", m1.get(), m2.get(), s1 == s2);
for (unsigned i = 0; i < 6; i++)
{
m1.update256(s1[i]);
m2.update256(s2[i]);
}
LOG(INFO, "2 %02x %02x", m1.get(), m2.get());
for (unsigned i = 0; i < 6; i++)
{
m1.update256(s1[i]);
m2.update256(s2[i]);
}
LOG(INFO, "3 %02x %02x", m1.get(), m2.get());
for (unsigned cc = 0; cc < 256; cc++)
{
m1.init();
m1.update256(cc);
m2.init();
m2.update256(cc);
for (unsigned i = 0; i < 6; i++)
{
m1.update256(s1[i]);
m2.update256(s2[i]);
}
LOG(VERBOSE, "start %02x one %02x two %02x", cc, m1.get(), m2.get());
}
LOG(INFO, "s1=%s s2=%s", string_to_hex(s1).c_str(),
string_to_hex(s2).c_str());
}