diff --git a/libc/test/src/math/fdiml_test.cpp b/libc/test/src/math/fdiml_test.cpp
@@ -0,0 +1,27 @@
+//===-- Unittests for fdiml -----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "FDimTest.h"
+
+#include "include/math.h"
+#include "src/math/fdiml.h"
+#include "utils/FPUtil/FPBits.h"
+#include "utils/FPUtil/TestHelpers.h"
+#include "utils/UnitTest/Test.h"
+
+using FDimTest = FDimTestTemplate<long double>;
+
+TEST_F(FDimTest, NaNArg_fdiml) { testNaNArg(&__llvm_libc::fdiml); }
+
+TEST_F(FDimTest, InfArg_fdiml) { testInfArg(&__llvm_libc::fdiml); }
+
+TEST_F(FDimTest, NegInfArg_fdiml) { testNegInfArg(&__llvm_libc::fdiml); }
+
+TEST_F(FDimTest, BothZero_fdiml) { testBothZero(&__llvm_libc::fdiml); }
+
+TEST_F(FDimTest, InLongDoubleRange_fdiml) { testInRange(&__llvm_libc::fdiml); }
diff --git a/libc/utils/FPUtil/BasicOperations.h b/libc/utils/FPUtil/BasicOperations.h
@@ -62,6 +62,22 @@ static inline T fmax(T x, T y) {
   }
 }
 
+template <typename T,
+          cpp::EnableIfType<cpp::IsFloatingPointType<T>::Value, int> = 0>
+static inline T fdim(T x, T y) {
+  FPBits<T> bitx(x), bity(y);
+
+  if (bitx.isNaN()) {
+    return x;
+  }
+
+  if (bity.isNaN()) {
+    return y;
+  }
+
+  return (x > y ? x - y : 0);
+}
+
 } // namespace fputil
 } // namespace __llvm_libc