[libc-commits] [libc] [libc][mathvec] Initial commit for LIBC vector math component (PR #173058)

[Schrodinger ZHU Yifan via libc-commits]

================
@@ -0,0 +1,29 @@
+//===-- Common utils for exp function ---------------------------*- 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_SRC___SUPPORT_MATHVEC_EXP_UTILS_H
+#define LLVM_LIBC_SRC___SUPPORT_MATHVEC_EXP_UTILS_H
+
+#include "src/__support/CPP/simd.h"
+#include "src/__support/mathvec/common_constants.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+template <size_t N>
+LIBC_INLINE cpp::simd<double, N> exp_lookup(cpp::simd<uint64_t, N> u) {
+  auto index = u & cpp::simd<uint64_t, N>(0x3f);
+  auto mantissa = cpp::gather<cpp::simd<uint64_t, N>>(
+      true, index, common_constants_internal::EXP_MANTISSA);
+  auto exponent = (u >> 6) << 52;
+  auto result = mantissa | exponent;
+  return reinterpret_cast<cpp::simd<double, N>>(result);
----------------
SchrodingerZhu wrote:

It feels strange to do `reinterpret_cast` from a simd register of integer to a simd register of double.

```suggestion
  return cpp::bit_cast<cpp::simd<double, N>>(result);
```

https://github.com/llvm/llvm-project/pull/173058