[libc-commits] [libc] [libc][math][c23] implement C23 math function asinpif16 (PR #146226)

[via libc-commits]

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@@ -0,0 +1,163 @@
+//===-- Half-precision asinpif16(x) function ------------------------------===//
+//
+// 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.
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/math/asinpif16.h"
+#include "hdr/errno_macros.h"
+#include "hdr/fenv_macros.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/PolyEval.h"
+#include "src/__support/FPUtil/cast.h"
+#include "src/__support/FPUtil/except_value_utils.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/FPUtil/sqrt.h"
+#include "src/__support/macros/optimization.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+static constexpr float16 ONE_OVER_TWO = 0.5f16;
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+static constexpr size_t N_ASINFPI_EXCEPTS = 3;
+
+static constexpr fputil::ExceptValues<float16, N_ASINFPI_EXCEPTS>
+    ASINFPI_EXCEPTS{{
+        // (input_hex, RZ_output_hex, RU_offset, RD_offset, RN_offset)
+        // x = 0.0, asinfpi(0.0) = 0.0
+        {0x0000, 0x0000, 0, 0, 0},
+
+        // x = 1.0, asinfpi(1) = 1/2
+        {(fputil::FPBits<float16>(1.0f16)).uintval(),
+         (fputil::FPBits<float16>(ONE_OVER_TWO)).uintval(), 0, 0, 0},
+
+        // x = -1.0, asinfpi(-1.0) = -1/2
+        {(fputil::FPBits<float16>(-1.0f16)).uintval(),
+         (fputil::FPBits<float16>(-ONE_OVER_TWO)).uintval(), 0, 0, 0},
+    }};
----------------
overmighty wrote:

Exceptional values with the degree-13 polynomial:

```cpp
        // x = 0x1.004p-3, asinpif16(x) = 0x1.47p-5 (RZ)
        {0x3001U, 0x291cU, 1U, 0U, 1U},
        // x = 0x1.0bp-1, asinpif16(x) = 0x1.658p-3 (RZ)
        {0x382cU, 0x3196U, 1U, 0U, 0U},
```

Exceptional values with the degree-11 polynomial:

```cpp
        // x = 0x1.004p-3, asinpif16(x) = 0x1.47p-5 (RZ)
        {0x3001U, 0x291cU, 1U, 0U, 1U},
        // x = 0x1.e3cp-2, asinpif16(x) = 0x1.40cp-3 (RZ)
        {0x378fU, 0x3103U, 1U, 0U, 0U},
        // x = 0x1.0bp-1, asinpif16(x) = 0x1.658p-3 (RZ)
        {0x382cU, 0x3196U, 1U, 0U, 0U},
        // x = 0x1.0b4p-1, asinpif16(x) = 0x1.65cp-3 (RZ)
        {0x382dU, 0x3197U, 1U, 0U, 1U},
        // x = 0x1.124p-1, asinpif16(x) = 0x1.704p-3 (RZ)
        {0x3849U, 0x31c1U, 1U, 0U, 1U},
```

https://github.com/llvm/llvm-project/pull/146226