88 lines
3.6 KiB
C++
88 lines
3.6 KiB
C++
// Licensed to the Apache Software Foundation (ASF) under one
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// or more contributor license agreements. See the NOTICE file
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// distributed with this work for additional information
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// regarding copyright ownership. The ASF licenses this file
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// to you under the Apache License, Version 2.0 (the
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// "License"); you may not use this file except in compliance
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// with the License. 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,
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// software distributed under the License is distributed on an
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// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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// KIND, either express or implied. See the License for the
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// specific language governing permissions and limitations
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// under the License.
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// This file is copied from
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// https://github.com/ClickHouse/ClickHouse/blob/master/src/Common/MemcpySmall.h
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// and modified by Doris
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#pragma once
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#include <string.h>
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#if defined(__SSE2__) || defined(__aarch64__)
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#ifdef __SSE2__
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#include <emmintrin.h>
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#elif __aarch64__
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#include <sse2neon.h>
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#endif
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/** memcpy function could work suboptimal if all the following conditions are met:
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* 1. Size of memory region is relatively small (approximately, under 50 bytes).
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* 2. Size of memory region is not known at compile-time.
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*
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* In that case, memcpy works suboptimal by following reasons:
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* 1. Function is not inlined.
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* 2. Much time/instructions are spend to process "tails" of data.
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*
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* There are cases when function could be implemented in more optimal way, with help of some assumptions.
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* One of that assumptions - ability to read and write some number of bytes after end of passed memory regions.
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* Under that assumption, it is possible not to implement difficult code to process tails of data and do copy always by big chunks.
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*
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* This case is typical, for example, when many small pieces of data are gathered to single contiguous piece of memory in a loop.
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* - because each next copy will overwrite excessive data after previous copy.
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*
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* Assumption that size of memory region is small enough allows us to not unroll the loop.
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* This is slower, when size of memory is actually big.
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*
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* Use with caution.
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*/
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namespace detail {
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inline void memcpy_small_allow_read_write_overflow15_impl(char* __restrict dst,
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const char* __restrict src, ssize_t n) {
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while (n > 0) {
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_mm_storeu_si128(reinterpret_cast<__m128i*>(dst),
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_mm_loadu_si128(reinterpret_cast<const __m128i*>(src)));
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dst += 16;
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src += 16;
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n -= 16;
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}
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}
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} // namespace detail
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/** Works under assumption, that it's possible to read up to 15 excessive bytes after end of 'src' region
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* and to write any garbage into up to 15 bytes after end of 'dst' region.
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*/
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inline void memcpy_small_allow_read_write_overflow15(void* __restrict dst,
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const void* __restrict src, size_t n) {
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detail::memcpy_small_allow_read_write_overflow15_impl(reinterpret_cast<char*>(dst),
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reinterpret_cast<const char*>(src), n);
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}
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/** NOTE There was also a function, that assumes, that you could read any bytes inside same memory page of src.
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* This function was unused, and also it requires special handling for Valgrind and ASan.
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*/
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#else /// Implementation for other platforms.
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inline void memcpy_small_allow_read_write_overflow15(void* __restrict dst,
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const void* __restrict src, size_t n) {
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memcpy(dst, src, n);
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}
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#endif
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