129 lines
4.7 KiB
C++
129 lines
4.7 KiB
C++
// Copyright 2020 Google LLC
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// SPDX-License-Identifier: Apache-2.0
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "hwy/examples/skeleton.h"
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#include <stdio.h>
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// >>>> for dynamic dispatch only, skip if you want static dispatch
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// First undef to prevent error when re-included.
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#undef HWY_TARGET_INCLUDE
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// For dynamic dispatch, specify the name of the current file (unfortunately
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// __FILE__ is not reliable) so that foreach_target.h can re-include it.
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#define HWY_TARGET_INCLUDE "hwy/examples/skeleton.cc"
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// Generates code for each enabled target by re-including this source file.
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#include "hwy/foreach_target.h" // IWYU pragma: keep
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// <<<< end of dynamic dispatch
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// Must come after foreach_target.h to avoid redefinition errors.
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#include "hwy/highway.h"
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// Optional, can instead add HWY_ATTR to all functions.
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HWY_BEFORE_NAMESPACE();
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namespace skeleton {
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// This namespace name is unique per target, which allows code for multiple
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// targets to co-exist in the same translation unit. Required when using dynamic
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// dispatch, otherwise optional.
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namespace HWY_NAMESPACE {
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// Highway ops reside here; ADL does not find templates nor builtins.
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namespace hn = hwy::HWY_NAMESPACE;
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// Computes log2 by converting to a vector of floats. Compiled once per target.
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template <class DF>
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HWY_ATTR_NO_MSAN void OneFloorLog2(const DF df,
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const uint8_t* HWY_RESTRICT values,
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uint8_t* HWY_RESTRICT log2) {
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// Type tags for converting to other element types (Rebind = same count).
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const hn::RebindToSigned<DF> d32;
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const hn::Rebind<uint8_t, DF> d8;
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using VI32 = hn::Vec<decltype(d32)>;
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const VI32 vi32 = hn::PromoteTo(d32, hn::Load(d8, values));
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const VI32 bits = hn::BitCast(d32, hn::ConvertTo(df, vi32));
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const VI32 exponent = hn::Sub(hn::ShiftRight<23>(bits), hn::Set(d32, 127));
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hn::Store(hn::DemoteTo(d8, exponent), d8, log2);
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}
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void CodepathDemo() {
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// Highway defaults to portability, but per-target codepaths may be selected
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// via #if HWY_TARGET == HWY_SSE4 or by testing capability macros:
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#if HWY_HAVE_INTEGER64
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const char* gather = "Has int64";
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#else
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const char* gather = "No int64";
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#endif
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printf("Target %s: %s\n", hwy::TargetName(HWY_TARGET), gather);
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}
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void FloorLog2(const uint8_t* HWY_RESTRICT values, size_t count,
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uint8_t* HWY_RESTRICT log2) {
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CodepathDemo();
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const hn::ScalableTag<float> df;
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const size_t N = hn::Lanes(df);
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size_t i = 0;
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for (; i + N <= count; i += N) {
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OneFloorLog2(df, values + i, log2 + i);
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}
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for (; i < count; ++i) {
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hn::CappedTag<float, 1> d1;
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OneFloorLog2(d1, values + i, log2 + i);
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}
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}
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// NOLINTNEXTLINE(google-readability-namespace-comments)
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} // namespace HWY_NAMESPACE
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} // namespace skeleton
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HWY_AFTER_NAMESPACE();
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// The table of pointers to the various implementations in HWY_NAMESPACE must
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// be compiled only once (foreach_target #includes this file multiple times).
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// HWY_ONCE is true for only one of these 'compilation passes'.
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#if HWY_ONCE
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namespace skeleton {
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// This macro declares a static array used for dynamic dispatch; it resides in
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// the same outer namespace that contains FloorLog2.
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HWY_EXPORT(FloorLog2);
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// This function is optional and only needed in the case of exposing it in the
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// header file. Otherwise using HWY_DYNAMIC_DISPATCH(FloorLog2) in this module
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// is equivalent to inlining this function.
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HWY_DLLEXPORT void CallFloorLog2(const uint8_t* HWY_RESTRICT in,
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const size_t count,
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uint8_t* HWY_RESTRICT out) {
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// This must reside outside of HWY_NAMESPACE because it references (calls the
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// appropriate one from) the per-target implementations there.
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// For static dispatch, use HWY_STATIC_DISPATCH.
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return HWY_DYNAMIC_DISPATCH(FloorLog2)(in, count, out);
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}
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HWY_DLLEXPORT void SavedCallFloorLog2(const uint8_t* HWY_RESTRICT in,
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const size_t count,
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uint8_t* HWY_RESTRICT out) {
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const auto ptr = HWY_DYNAMIC_POINTER(FloorLog2);
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return ptr(in, count, out);
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}
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// Optional: anything to compile only once, e.g. non-SIMD implementations of
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// public functions provided by this module, can go inside #if HWY_ONCE.
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} // namespace skeleton
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#endif // HWY_ONCE
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