7f19d64164
git-subtree-dir: third_party/immer git-subtree-split: ad3e3556d38bb75966dd24c61a774970a7c7957e
108 lines
2.5 KiB
C++
108 lines
2.5 KiB
C++
//
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// immer: immutable data structures for C++
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// Copyright (C) 2016, 2017, 2018 Juan Pedro Bolivar Puente
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//
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// This software is distributed under the Boost Software License, Version 1.0.
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// See accompanying file LICENSE or copy at http://boost.org/LICENSE_1_0.txt
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//
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#pragma once
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#include <cstdint>
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#if defined(_MSC_VER)
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#include <intrin.h> // __popcnt
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#endif
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namespace immer {
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namespace detail {
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namespace hamts {
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using size_t = std::size_t;
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using hash_t = std::size_t;
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using bits_t = std::uint32_t;
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using count_t = std::uint32_t;
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using shift_t = std::uint32_t;
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template <bits_t B>
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struct get_bitmap_type
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{
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static_assert(B < 6u, "B > 6 is not supported.");
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using type = std::uint32_t;
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};
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template <>
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struct get_bitmap_type<6u>
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{
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using type = std::uint64_t;
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};
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template <bits_t B, typename T = count_t>
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constexpr T branches = T{1u} << B;
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template <bits_t B, typename T = size_t>
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constexpr T mask = branches<B, T> - 1u;
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template <bits_t B, typename T = count_t>
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constexpr T max_depth = (sizeof(hash_t) * 8u + B - 1u) / B;
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template <bits_t B, typename T = count_t>
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constexpr T max_shift = max_depth<B, count_t>* B;
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#define IMMER_HAS_BUILTIN_POPCOUNT 1
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inline auto popcount_fallback(std::uint32_t x)
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{
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// More alternatives:
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// https://en.wikipedia.org/wiki/Hamming_weight
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// http://wm.ite.pl/articles/sse-popcount.html
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// http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
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x = x - ((x >> 1) & 0x55555555u);
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x = (x & 0x33333333u) + ((x >> 2) & 0x33333333u);
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return (((x + (x >> 4u)) & 0xF0F0F0Fu) * 0x1010101u) >> 24u;
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}
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inline auto popcount_fallback(std::uint64_t x)
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{
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x = x - ((x >> 1) & 0x5555555555555555u);
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x = (x & 0x3333333333333333u) + ((x >> 2u) & 0x3333333333333333u);
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return (((x + (x >> 4)) & 0x0F0F0F0F0F0F0F0Fu) * 0x0101010101010101u) >>
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56u;
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}
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inline count_t popcount(std::uint32_t x)
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{
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#if IMMER_HAS_BUILTIN_POPCOUNT
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#if defined(_MSC_VER)
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return __popcnt(x);
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#else
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return __builtin_popcount(x);
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#endif
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#else
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return popcount_fallback(x);
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#endif
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}
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inline count_t popcount(std::uint64_t x)
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{
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#if IMMER_HAS_BUILTIN_POPCOUNT
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#if defined(_MSC_VER)
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#if defined(_WIN64)
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return __popcnt64(x);
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#else
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// TODO: benchmark against popcount_fallback(std::uint64_t x)
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return popcount(static_cast<std::uint32_t>(x >> 32)) +
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popcount(static_cast<std::uint32_t>(x));
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#endif
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#else
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return __builtin_popcountll(x);
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#endif
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#else
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return popcount_fallback(x);
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#endif
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}
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} // namespace hamts
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} // namespace detail
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} // namespace immer
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