Skip to content

fix computation of serial correlation factor scct1 #1771

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Aug 22, 2022
Merged

fix computation of serial correlation factor scct1 #1771

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
10 changes: 8 additions & 2 deletions libyara/modules/math/math.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -319,6 +319,7 @@ define_function(data_serial_correlation)
YR_MEMORY_BLOCK_ITERATOR* iterator = context->iterator;

double sccun = 0;
double sccfirst = 0;
double scclast = 0;
double scct1 = 0;
double scct2 = 0;
Expand Down Expand Up @@ -348,6 +349,9 @@ define_function(data_serial_correlation)
for (i = 0; i < data_len; i++)
{
sccun = (double) *(block_data + data_offset + i);
if (i == 0) {
sccfirst = sccun;
}
scct1 += scclast * sccun;
scct2 += sccun;
scct3 += sccun * sccun;
Expand All @@ -373,7 +377,7 @@ define_function(data_serial_correlation)
if (!past_first_block)
return_float(YR_UNDEFINED);

scct1 += scclast * sccun;
scct1 += scclast * sccfirst;
scct2 *= scct2;

scc = total_len * scct3 - scct2;
Expand Down Expand Up @@ -408,7 +412,9 @@ define_function(string_serial_correlation)
scclast = sccun;
}

scct1 += scclast * sccun;
if (s->length > 0) {
scct1 += scclast * (double) s->c_string[0];
}
scct2 *= scct2;

scc = s->length * scct3 - scct2;
Expand Down
4 changes: 2 additions & 2 deletions tests/test-math.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -179,15 +179,15 @@ int main(int argc, char** argv)
"import \"math\" \
rule test { \
condition: \
math.serial_correlation(\"BCAB\") == -0.5 \
math.serial_correlation(\"BCA\") == -0.5 \
}",
NULL);

assert_true_rule_blob(
"import \"math\" \
rule test { \
condition: \
math.serial_correlation(1, 4) == -0.5 \
math.serial_correlation(1, 3) == -0.5 \
}",
"ABCABC");

Expand Down