[libc] added cos function fuzzing test (#101556)

libc/fuzzing/math/CMakeLists.txt

@@ -70,3 +70,12 @@ add_libc_fuzzer(
   DEPENDS
     libc.src.math.sin
 )
+
+add_libc_fuzzer(
+  cos_fuzz
+  NEED_MPFR
+  SRCS
+    cos_fuzz.cpp
+  DEPENDS
+    libc.src.math.cos
+)

libc/fuzzing/math/cos_fuzz.cpp

@@ -0,0 +1,40 @@
+//===-- cos_fuzz.cpp ----------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// Fuzzing test for llvm-libc cos implementation.
+///
+//===----------------------------------------------------------------------===//
+
+#include "src/math/cos.h"
+#include <math.h>
+#include <mpfr.h>
+
+extern "C" int LLVMFuzzerTestOneInput(const double x) {
+  // remove NaN and inf as preconditions
+  if (isnan(x))
+    return 0;
+  if (isinf(x))
+    return 0;
+  // signed zeros already tested in unit tests
+  if (signbit(x) && x == 0.0)
+    return 0;
+  mpfr_t input;
+  mpfr_init2(input, 53);
+  mpfr_set_d(input, x, MPFR_RNDN);
+  int output = mpfr_cos(input, input, MPFR_RNDN);
+  mpfr_subnormalize(input, output, MPFR_RNDN);
+  double to_compare = mpfr_get_d(input, MPFR_RNDN);
+
+  double result = LIBC_NAMESPACE::cos(x);
+
+  if (result != to_compare)
+    __builtin_trap();
+
+  mpfr_clear(input);
+  return 0;
+}

libc/fuzzing/math/sin_fuzz.cpp

@@ -11,17 +11,17 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/math/sin.h"
-#include <cmath>
+#include <math.h>
 #include <mpfr.h>
 
 extern "C" int LLVMFuzzerTestOneInput(const double x) {
   // remove NaN and inf as preconditions
-  if (std::isnan(x))
+  if (isnan(x))
     return 0;
-  if (std::isinf(x))
+  if (isinf(x))
     return 0;
   // signed zeros already tested in unit tests
-  if (std::signbit(x) && x == 0.0)
+  if (signbit(x) && x == 0.0)
     return 0;
   mpfr_t input;
   mpfr_init2(input, 53);