[libc-commits] [libc] [llvm] [libc][math][c23] Add rsqrtf() function (PR #159615)

[via libc-commits]

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@@ -0,0 +1,74 @@
+//===-- Utility class to test rsqrt[f|l] ------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_TEST_SRC_MATH_RSQRTTEST_H
+#define LLVM_LIBC_TEST_SRC_MATH_RSQRTTEST_H
+
+#include "test/UnitTest/FEnvSafeTest.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+
+namespace mpfr = LIBC_NAMESPACE::testing::mpfr;
+
+template <typename OutType, typename InType = OutType>
+class RsqrtTest : public LIBC_NAMESPACE::testing::FEnvSafeTest {
+
+  DECLARE_SPECIAL_CONSTANTS(InType)
+
+  static constexpr StorageType HIDDEN_BIT =
+      StorageType(1) << LIBC_NAMESPACE::fputil::FPBits<InType>::FRACTION_LEN;
+
+public:
+  using RsqrtFunc = OutType (*)(InType);
+
+  // Subnormal inputs: probe both power-of-two mantissas and an even sampling
+  // across the subnormal range.
+  void test_denormal_values(RsqrtFunc func) {
+    // Powers of two in the subnormal mantissa space.
+    for (StorageType mant = 1; mant < HIDDEN_BIT; mant <<= 1) {
+      FPBits denormal(zero);
+      denormal.set_mantissa(mant);
+      InType x = denormal.get_val();
+      ASSERT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Rsqrt, x, func(x), 0.5);
+    }
+
+    // Even sampling across all subnormals.
+    constexpr StorageType COUNT = 200'001;
+    constexpr StorageType STEP = HIDDEN_BIT / COUNT;
+    for (StorageType i = 0, v = 0; i <= COUNT; ++i, v += STEP) {
+      InType x = FPBits(i).get_val();
+      ASSERT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Rsqrt, x, func(x), 0.5);
+    }
+  }
+
+  // Positive normal range sampling: skip NaNs and negative values.
+  void test_normal_range(RsqrtFunc func) {
+    constexpr StorageType COUNT = 200'001;
+    constexpr StorageType STEP = STORAGE_MAX / COUNT;
+    for (StorageType i = 0, v = 0; i <= COUNT; ++i, v += STEP) {
+      FPBits x_bits(v);
+      InType x = x_bits.get_val();
+      if (x_bits.is_nan() || (x < static_cast<InType>(0)))
----------------
overmighty wrote:

```suggestion
      if (x_bits.is_nan() || x_bits.is_neg())
```

https://github.com/llvm/llvm-project/pull/159615