[libc] sincos fuzz test (#147855)

Created fuzz test for sincos

---------

Co-authored-by: Sriya Pratipati <sriyap@google.com>

Author: sribee8

libc/fuzzing/math/CMakeLists.txt

@@ -88,3 +88,12 @@ add_libc_fuzzer(
   DEPENDS
     libc.src.math.tan
 )
+
+add_libc_fuzzer(
+  sincos_fuzz
+  NEED_MPFR
+  SRCS
+    sincos_fuzz.cpp
+  DEPENDS
+    libc.src.math.sincos
+)

libc/fuzzing/math/sincos_fuzz.cpp

@@ -0,0 +1,51 @@
+//===-- sincos_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/sincos.h"
+#include "utils/MPFRWrapper/mpfr_inc.h"
+#include <math.h>
+
+extern "C" int LLVMFuzzerTestOneInput(double x) {
+  // remove NaN and inf as preconditions
+  if (isnan(x) || isinf(x))
+    return 0;
+  // signed zeros already tested in unit tests
+  if (signbit(x) && x == 0.0)
+    return 0;
+  mpfr_t input;
+  mpfr_t sin_x;
+  mpfr_t cos_x;
+
+  mpfr_init2(input, 53);
+  mpfr_init2(sin_x, 53);
+  mpfr_init2(cos_x, 53);
+
+  mpfr_set_d(input, x, MPFR_RNDN);
+
+  int output = mpfr_sin_cos(sin_x, cos_x, input, MPFR_RNDN);
+  mpfr_subnormalize(sin_x, output, MPFR_RNDN);
+  mpfr_subnormalize(cos_x, output, MPFR_RNDN);
+
+  double to_compare_sin = mpfr_get_d(sin_x, MPFR_RNDN);
+  double to_compare_cos = mpfr_get_d(cos_x, MPFR_RNDN);
+
+  double sin_res, cos_res;
+  LIBC_NAMESPACE::sincos(x, &sin_res, &cos_res);
+
+  if (sin_res != to_compare_sin || cos_res != to_compare_cos)
+    __builtin_trap();
+
+  mpfr_clear(input);
+  mpfr_clear(sin_x);
+  mpfr_clear(cos_x);
+  return 0;
+}