Determine equality of floating point values as abs(A-B) < epsilon ins…

…tead of A == B. Precise equality can lead to wrong results due to small differences in values cause by rounding. Closes issue #561.
JusticeRage · Aug 2, 2018 · 803d42a · 803d42a
1 parent f9a52f0
commit 803d42a
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Showing 2 changed files with 24 additions and 2 deletions.
diff --git a/libyara/exec.c b/libyara/exec.c
@@ -32,6 +32,7 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <string.h>
 #include <assert.h>
 #include <math.h>
+#include <float.h>
 
 #include <yara/globals.h>
 #include <yara/arena.h>
@@ -1157,7 +1158,7 @@ int yr_execute_code(
         pop(r1);
         ensure_defined(r2);
         ensure_defined(r1);
-        r1.i = r1.d == r2.d;
+        r1.i = fabs(r1.d - r2.d) < DBL_EPSILON;
         push(r1);
         break;
 
@@ -1166,7 +1167,7 @@ int yr_execute_code(
         pop(r1);
         ensure_defined(r2);
         ensure_defined(r1);
-        r1.i = r1.d != r2.d;
+        r1.i = fabs(r1.d - r2.d) >= DBL_EPSILON;
         push(r1);
         break;
 

diff --git a/tests/test-rules.c b/tests/test-rules.c
@@ -88,6 +88,27 @@ static void test_comparison_operators()
   assert_true_rule(
       "rule test { condition: 1.5 >= 1.0}", NULL);
 
+  assert_true_rule(
+      "rule test { condition: 1.0 != 1.000000000000001 }", NULL);
+
+  assert_true_rule(
+      "rule test { condition: 1.0 < 1.000000000000001 }", NULL);
+
+  assert_false_rule(
+      "rule test { condition: 1.0 >= 1.000000000000001 }", NULL);
+
+  assert_true_rule(
+      "rule test { condition: 1.000000000000001 > 1 }", NULL);
+
+  assert_false_rule(
+      "rule test { condition: 1.000000000000001 <= 1 }", NULL);
+
+  assert_true_rule(
+      "rule test { condition: 1.0 == 1.0000000000000001 }", NULL);
+
+  assert_true_rule(
+      "rule test { condition: 1.0 >= 1.0000000000000001 }", NULL);
+
   assert_true_rule(
       "rule test { condition: 1.5 >= 1}", NULL);