[libc] created fuzz test for sin function

libc/fuzzing/CMakeLists.txt

@@ -3,7 +3,7 @@ add_custom_target(libc-fuzzer)
 
 add_subdirectory(__support)
 # TODO(#85680): Re-enable math fuzzing after headers are sorted out
-# add_subdirectory(math)
+add_subdirectory(math)
 add_subdirectory(stdlib)
 add_subdirectory(stdio)
 add_subdirectory(string)

libc/fuzzing/math/CMakeLists.txt

@@ -61,3 +61,12 @@ add_libc_fuzzer(
     libc.src.math.nextafterf
     libc.src.math.nextafterl
 )
+
+add_libc_fuzzer(
+  sin_fuzz
+  NEED_MPFR
+  SRCS
+    sin_fuzz.cpp
+  DEPENDS
+    libc.src.math.sin
+)

libc/fuzzing/math/sin_fuzz.cpp

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