1 files changed, 122 insertions, 0 deletions
diff --git a/third_party/highway/hwy/examples/skeleton.cc b/third_party/highway/hwy/examples/skeleton.cc
new file mode 100644
index 0000000000..778ba4ac0a
--- /dev/null
+++ b/third_party/highway/hwy/examples/skeleton.cc
@@ -0,0 +1,122 @@
+// Copyright 2020 Google LLC
+// SPDX-License-Identifier: Apache-2.0
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "hwy/examples/skeleton.h"
+
+#include <stdio.h>
+
+// >>>> for dynamic dispatch only, skip if you want static dispatch
+
+// First undef to prevent error when re-included.
+#undef HWY_TARGET_INCLUDE
+// For dynamic dispatch, specify the name of the current file (unfortunately
+// __FILE__ is not reliable) so that foreach_target.h can re-include it.
+#define HWY_TARGET_INCLUDE "hwy/examples/skeleton.cc"
+// Generates code for each enabled target by re-including this source file.
+#include "hwy/foreach_target.h"  // IWYU pragma: keep
+
+// <<<< end of dynamic dispatch
+
+// Must come after foreach_target.h to avoid redefinition errors.
+#include "hwy/highway.h"
+
+// Optional, can instead add HWY_ATTR to all functions.
+HWY_BEFORE_NAMESPACE();
+
+namespace skeleton {
+// This namespace name is unique per target, which allows code for multiple
+// targets to co-exist in the same translation unit. Required when using dynamic
+// dispatch, otherwise optional.
+namespace HWY_NAMESPACE {
+
+// Highway ops reside here; ADL does not find templates nor builtins.
+namespace hn = hwy::HWY_NAMESPACE;
+
+// Computes log2 by converting to a vector of floats. Compiled once per target.
+template <class DF>
+HWY_ATTR_NO_MSAN void OneFloorLog2(const DF df,
+                                   const uint8_t* HWY_RESTRICT values,
+                                   uint8_t* HWY_RESTRICT log2) {
+  // Type tags for converting to other element types (Rebind = same count).
+  const hn::RebindToSigned<DF> d32;
+  const hn::Rebind<uint8_t, DF> d8;
+  using VI32 = hn::Vec<decltype(d32)>;
+
+  const VI32 vi32 = hn::PromoteTo(d32, hn::Load(d8, values));
+  const VI32 bits = hn::BitCast(d32, hn::ConvertTo(df, vi32));
+  const VI32 exponent = hn::Sub(hn::ShiftRight<23>(bits), hn::Set(d32, 127));
+  hn::Store(hn::DemoteTo(d8, exponent), d8, log2);
+}
+
+void CodepathDemo() {
+  // Highway defaults to portability, but per-target codepaths may be selected
+  // via #if HWY_TARGET == HWY_SSE4 or by testing capability macros:
+#if HWY_HAVE_INTEGER64
+  const char* gather = "Has int64";
+#else
+  const char* gather = "No int64";
+#endif
+  printf("Target %s: %s\n", hwy::TargetName(HWY_TARGET), gather);
+}
+
+void FloorLog2(const uint8_t* HWY_RESTRICT values, size_t count,
+               uint8_t* HWY_RESTRICT log2) {
+  CodepathDemo();
+
+  const hn::ScalableTag<float> df;
+  const size_t N = hn::Lanes(df);
+  size_t i = 0;
+  for (; i + N <= count; i += N) {
+    OneFloorLog2(df, values + i, log2 + i);
+  }
+  for (; i < count; ++i) {
+    hn::CappedTag<float, 1> d1;
+    OneFloorLog2(d1, values + i, log2 + i);
+  }
+}
+
+// NOLINTNEXTLINE(google-readability-namespace-comments)
+}  // namespace HWY_NAMESPACE
+}  // namespace skeleton
+HWY_AFTER_NAMESPACE();
+
+// The table of pointers to the various implementations in HWY_NAMESPACE must
+// be compiled only once (foreach_target #includes this file multiple times).
+// HWY_ONCE is true for only one of these 'compilation passes'.
+#if HWY_ONCE
+
+namespace skeleton {
+
+// This macro declares a static array used for dynamic dispatch; it resides in
+// the same outer namespace that contains FloorLog2.
+HWY_EXPORT(FloorLog2);
+
+// This function is optional and only needed in the case of exposing it in the
+// header file. Otherwise using HWY_DYNAMIC_DISPATCH(FloorLog2) in this module
+// is equivalent to inlining this function.
+HWY_DLLEXPORT void CallFloorLog2(const uint8_t* HWY_RESTRICT in,
+                                 const size_t count,
+                                 uint8_t* HWY_RESTRICT out) {
+  // This must reside outside of HWY_NAMESPACE because it references (calls the
+  // appropriate one from) the per-target implementations there.
+  // For static dispatch, use HWY_STATIC_DISPATCH.
+  return HWY_DYNAMIC_DISPATCH(FloorLog2)(in, count, out);
+}
+
+// Optional: anything to compile only once, e.g. non-SIMD implementations of
+// public functions provided by this module, can go inside #if HWY_ONCE.
+
+}  // namespace skeleton
+#endif  // HWY_ONCE