[libc-commits] [libc] [libc][math][c23] Add acoshf16 C23 math function. (PR #130588)

[via libc-commits]

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@@ -0,0 +1,88 @@
+//===-- Half-precision acoshf16 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/acoshf16.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/cast.h"
+#include "src/__support/FPUtil/except_value_utils.h"
+#include "src/__support/FPUtil/generic/sqrt.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/macros/optimization.h"
+#include "src/math/generic/explogxf.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+static constexpr size_t N_EXCEPTS = 2;
+static constexpr fputil::ExceptValues<float16, N_EXCEPTS> ACOSHF16_EXCEPTS{
+    {// (input, RZ output, RU offset, RD offset, RN offset)
+     {0x41B7, 0x3ED8, 1, 0, 0},
+     {0x3CE4, 0x393E, 1, 0, 1}}};
+
+LLVM_LIBC_FUNCTION(float16, acoshf16, (float16 x)) {
+  using FPBits = fputil::FPBits<float16>;
+  FPBits xbits(x);
+  uint16_t x_u = xbits.uintval();
+  uint16_t x_abs = x_u & 0x7fff;
+
+  // Check for NaN input first.
+  if (LIBC_UNLIKELY(xbits.is_nan())) {
+    if (xbits.is_signaling_nan()) {
+      fputil::raise_except_if_required(FE_INVALID);
+      return FPBits::quiet_nan().get_val();
+    }
+    return x;
+  }
+
+  // Check for infinite inputs.
+  if (LIBC_UNLIKELY(xbits.is_inf())) {
+    if (xbits.is_neg()) {
+      fputil::set_errno_if_required(EDOM);
+      fputil::raise_except_if_required(FE_INVALID);
+      return FPBits::quiet_nan().get_val();
+    }
+    return x;
+  }
+
+  // Domain error for inputs less than 1.0.
+  if (LIBC_UNLIKELY(x_abs < 0x3c00U)) {
+    fputil::set_errno_if_required(EDOM);
+    fputil::raise_except_if_required(FE_INVALID);
+    return FPBits::quiet_nan().get_val();
+  }
+
+  // acosh(1.0) exactly equals 0.0
+  if (LIBC_UNLIKELY(x_u == 0x3c00U))
+    return float16(0.0f);
----------------
overmighty wrote:

Nit: I don't think this use of function-style casts is common across the LLVM libc codebase. I think we mostly use them when dealing with type template parameters.

```suggestion
    return FPBits::zero().get_val();;
```

https://github.com/llvm/llvm-project/pull/130588