[libc-commits] [libc] [libc][math][c23] Add asinhf16 function (PR #131351)

[via libc-commits]

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@@ -0,0 +1,106 @@
+//===-- Half-precision asinh(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/asinhf16.h"
+#include "explogxf.h"
+#include "hdr/fenv_macros.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/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+static constexpr size_t N_EXCEPTS = 8;
+
+static constexpr fputil::ExceptValues<float16, N_EXCEPTS> ASINHF16_EXCEPTS{{
+    // (input, RZ output, RU offset, RD offset, RN offset)
+
+    // x = 0x1.da4p-2, asinhf16(x) = 0x1.ca8p-2 (RZ)
+    {0x3769, 0x372a, 1, 0, 1},
+    // x = 0x1.d6cp-1, asinhf16(x) = 0x1.a58p-1 (RZ)
+    {0x3b5b, 0x3a96, 1, 0, 0},
+    // x = 0x1.c7cp+3, asinhf16(x) = 0x1.accp+1 (RZ)
+    {0x4b1f, 0x42b3, 1, 0, 0},
+    // x = 0x1.26cp+4, asinhf16(x) = 0x1.cd8p+1 (RZ)
+    {0x4c9b, 0x4336, 1, 0, 1},
+    // x = -0x1.da4p-2, asinhf16(x) = -0x1.ca8p-2 (RZ)
+    {0xb769, 0xb72a, 0, 1, 1},
+    // x = -0x1.d6cp-1, asinhf16(x) = -0x1.a58p-1 (RZ)
+    {0xbb5b, 0xba96, 0, 1, 0},
+    // x = -0x1.c7cp+3, asinhf16(x) = -0x1.accp+1 (RZ)
+    {0xcb1f, 0xc2b3, 0, 1, 0},
+    // x = -0x1.26cp+4, asinhf16(x) = -0x1.cd8p+1 (RZ)
+    {0xcc9b, 0xc336, 0, 1, 1},
+}};
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+LLVM_LIBC_FUNCTION(float16, asinhf16, (float16 x)) {
+  using FPBits = fputil::FPBits<float16>;
+  FPBits xbits(x);
+
+  uint16_t x_u = xbits.uintval();
+  uint16_t x_abs = x_u & 0x7fff;
+
+  if (LIBC_UNLIKELY(xbits.is_inf_or_nan())) {
+    if (xbits.is_signaling_nan()) {
+      fputil::raise_except_if_required(FE_INVALID);
+      return FPBits::quiet_nan().get_val();
+    }
+
+    return x;
+  }
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+  // Handle exceptional values
+  if (auto r = ASINHF16_EXCEPTS.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+    return r.value();
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+  float xf = x;
+  const float SIGN[2] = {1.0f, -1.0f};
+  float x_sign = SIGN[x_u >> 15];
+
+  // |x| <= 0.25
+  if (LIBC_UNLIKELY(x_abs <= 0x3400)) {
+
+    // when |x| < 0x1.718p-5, asinhf16(x) = x. Adjust by 1 ULP for certain
+    // rounding types.
+    if (LIBC_UNLIKELY(x_abs < 0x29c6)) {
+      if (((fputil::get_round() == FE_UPWARD) ||
+           (fputil::get_round() == FE_TOWARDZERO)) &&
+          xf < 0)
+        return fputil::cast<float16>(xf + 0x1p-24f);
+      if (((fputil::get_round() == FE_DOWNWARD) ||
+           (fputil::get_round() == FE_TOWARDZERO)) &&
+          xf > 0)
+        return fputil::cast<float16>(xf - 0x1p-24f);
+      return fputil::cast<float16>(xf);
+    }
+
+    float x_sq = xf * xf;
+    // Generated by Sollya with:
+    // > P = fpminimax(asinh(x)/x, [|0, 2, 4, 6, 8|], [|SG...|], [0, 2^-2]);
+    // The last coefficient 0x1.bd114ep-6f has been changed to 0x1.bd114ep-5f
+    // for better accuracy.
+    float p = fputil::polyeval(x_sq, 1.0f, -0x1.555552p-3f, 0x1.332f6ap-4f,
+                               -0x1.6c53dep-5f, 0x1.bd114ep-5f);
+
+    return fputil::cast<float16>(xf * p);
+  }
+
+  // General case: asinh(x) = ln(x + sqrt(x^2 + 1))
+  float sqrt_term = fputil::sqrt<float>(fputil::multiply_add(xf, xf, 1.0f));
+  return fputil::cast<float16>(
+      x_sign * log_eval(fputil::multiply_add(xf, x_sign, sqrt_term)));
+}
+} // namespace LIBC_NAMESPACE_DECL
----------------
overmighty wrote:

Nit: spacing.

```suggestion
}

} // namespace LIBC_NAMESPACE_DECL
```

https://github.com/llvm/llvm-project/pull/131351