[libc] cbrt fuzz test

libc/fuzzing/math/CMakeLists.txt

@@ -196,3 +196,12 @@ add_libc_fuzzer(
   DEPENDS
     libc.src.__support.FPUtil.generic.sqrt
 )
+
+add_libc_fuzzer(
+  cbrt_fuzz
+  NEED_MPFR
+  SRCS
+    cbrt_fuzz.cpp
+  DEPENDS
+    libc.src.math.cbrt
+)

libc/fuzzing/math/cbrt_fuzz.cpp

@@ -0,0 +1,50 @@
+//===-- cbrt_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 cbrt implementation.
+///
+//===----------------------------------------------------------------------===//
+
+#include "src/math/cbrt.h"
+#include "utils/MPFRWrapper/mpfr_inc.h"
+#include <cstdint>
+#include <cstring>
+#include <iostream>
+#include <math.h>
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+  mpfr_t input;
+  mpfr_init2(input, 53);
+  for (size_t i = 0; i < size / sizeof(double); ++i) {
+    double x;
+    std::memcpy(&x, data, sizeof(double));
+    data += sizeof(double);
+    // remove NaN and inf
+    if (isnan(x) || isinf(x))
+      continue;
+    // signed zeros already tested in unit tests
+    if (signbit(x) && x == 0.0)
+      continue;
+
+    mpfr_set_d(input, x, MPFR_RNDN);
+    int output = mpfr_cbrt(input, input, MPFR_RNDN);
+    mpfr_subnormalize(input, output, MPFR_RNDN);
+    double to_compare = mpfr_get_d(input, MPFR_RNDN);
+
+    double result = LIBC_NAMESPACE::cbrt(x);
+
+    if (result != to_compare) {
+      std::cout << std::hexfloat << "Failing input: " << x << std::endl;
+      std::cout << std::hexfloat << "Failing output: " << result << std::endl;
+      std::cout << std::hexfloat << "Expected: " << to_compare << std::endl;
+      __builtin_trap();
+    }
+  }
+  mpfr_clear(input);
+  return 0;
+}