bf9a963582
They're marked constinit, but constinit does not imply const. Since they're not supposed to be modified, mark them const too. Closes scylladb/scylladb#25539
66 lines
1.9 KiB
C++
66 lines
1.9 KiB
C++
/*
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* Copyright (C) 2018-present ScyllaDB
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*/
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/*
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* SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.0
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*
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*/
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#if defined(__x86_64__) || defined(__i386__) || defined(__aarch64__)
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#include <array>
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#include "crc_combine_table.hh"
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#include "utils/clmul.hh"
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#include "barrett.hh"
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template <int bits>
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static
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constexpr
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std::array<uint32_t, bits>
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make_crc32_power_table() {
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std::array<uint32_t, bits> pows;
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pows[0] = 0x00800000; // x^8
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for (int i = 1; i < bits; ++i) {
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// x^(2*N) mod G(x)
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// = (x^N)*(x^N) mod G(x)
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// = (x^N mod G(x))^2 mod G(x)
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pows[i] = crc32_fold_barrett_u64(clmul(pows[i - 1], pows[i - 1]) << 1);
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}
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return pows;
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}
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static
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constexpr
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std::array<uint32_t, 256>
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make_crc32_table(int base, int radix_bits, uint32_t one, std::array<uint32_t, 32> pows) {
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std::array<uint32_t, 256> table;
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for (int i = 0; i < (1 << radix_bits); ++i) {
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uint32_t product = one;
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for (int j = 0; j < radix_bits; ++j) {
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if (i & (1 << j)) {
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product = crc32_fold_barrett_u64(clmul(product, pows[base + j]) << 1);
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}
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}
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table[i] = product;
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}
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return table;
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}
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static constexpr int bits = 32;
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static constexpr int radix_bits = 8;
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static constexpr uint32_t one = 0x80000000; // x^0
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static constexpr auto pows = make_crc32_power_table<bits>(); // pows[i] = x^(2^i*8) mod G(x)
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const constinit std::array<uint32_t, 256> crc32_x_pow_radix_8_table_base_0 = make_crc32_table(0, radix_bits, one, pows);
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const constinit std::array<uint32_t, 256> crc32_x_pow_radix_8_table_base_8 = make_crc32_table(8, radix_bits, one, pows);
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const constinit std::array<uint32_t, 256> crc32_x_pow_radix_8_table_base_16 = make_crc32_table(16, radix_bits, one, pows);
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const constinit std::array<uint32_t, 256> crc32_x_pow_radix_8_table_base_24 = make_crc32_table(24, radix_bits, one, pows);
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#else
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#error "Not implemented for this CPU architecture."
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#endif
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