From 90065da6d5a5f661b60c2f75b0f2dc094d27f4f5 Mon Sep 17 00:00:00 2001
From: RoseZhang03 <rosezhang@google.com>
Date: Thu, 1 Aug 2024 17:31:04 +0000
Subject: [PATCH] [libc] created fuzz test for sin function (#101411)

Verifies that sin function output is correct by comparing with MPFR
output. NaN and inf are not tested (as our output will vary compared to
MPFR), and signed zeroes are already tested in unit tests.
---
 libc/fuzzing/CMakeLists.txt      |  2 +-
 libc/fuzzing/math/CMakeLists.txt |  9 +++++++
 libc/fuzzing/math/sin_fuzz.cpp   | 40 ++++++++++++++++++++++++++++++++
 3 files changed, 50 insertions(+), 1 deletion(-)
 create mode 100644 libc/fuzzing/math/sin_fuzz.cpp

diff --git a/libc/fuzzing/CMakeLists.txt b/libc/fuzzing/CMakeLists.txt
index 816691b4bd44..e2dcecca7f7d 100644
--- a/libc/fuzzing/CMakeLists.txt
+++ b/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)
diff --git a/libc/fuzzing/math/CMakeLists.txt b/libc/fuzzing/math/CMakeLists.txt
index 6990a04922a5..ad163cc53eae 100644
--- a/libc/fuzzing/math/CMakeLists.txt
+++ b/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
+)
diff --git a/libc/fuzzing/math/sin_fuzz.cpp b/libc/fuzzing/math/sin_fuzz.cpp
new file mode 100644
index 000000000000..1e607d461978
--- /dev/null
+++ b/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;
+}