2 files changed, 12 insertions, 0 deletions
diff --git a/Libraries/LibM/math.cpp b/Libraries/LibM/math.cpp
index ffa6483ccb..fc1e1ec38a 100644
--- a/Libraries/LibM/math.cpp
+++ b/Libraries/LibM/math.cpp
@@ -536,4 +536,11 @@ double erfc(double x)
 {
     return 1 - erf(x);
 }
+
+int isnormal(double x)
+{
+    if (x < 0)
+        x = -x;
+    return x >= DOUBLE_MIN && x <= DOUBLE_MAX;
+}
 }
diff --git a/Libraries/LibM/math.h b/Libraries/LibM/math.h
index 36b971560f..2783f1af59 100644
--- a/Libraries/LibM/math.h
+++ b/Libraries/LibM/math.h
@@ -42,6 +42,9 @@ __BEGIN_DECLS
 #define M_SQRT2 1.4142135623730951
 #define M_SQRT1_2 0.7071067811865475
 
+#define DOUBLE_MAX ((double)0b0111111111101111111111111111111111111111111111111111111111111111)
+#define DOUBLE_MIN ((double)0b0000000000010000000000000000000000000000000000000000000000000000)
+
 double acos(double);
 float acosf(float);
 double asin(double);
@@ -110,4 +113,6 @@ double hypot(double, double);
 double erf(double);
 double erfc(double);
 
+int isnormal(double);
+
 __END_DECLS