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33 lines
855 B
C++
33 lines
855 B
C++
// Copyright 2025 XTX Markets Technologies Limited
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//
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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#pragma once
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#include <stdint.h>
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constexpr uint32_t ISCSI_POLY = 0x82F63B78u;
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// Return a(x) multiplied by b(x) modulo ISCSI_POLY, For speed, this requires
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// that a(x) not be zero.
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static uint32_t crc32c_mult_mod_p(uint32_t a, uint32_t b) {
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// m goes from x^0 to x^31
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uint32_t m = 1u << 31;
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uint32_t p = 0;
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for (;;) {
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// If a(x) contains x^n, add b(x)*x^n
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if (a & m) {
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p ^= b;
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// Exit when there are no higher bits in a(x)
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if ((a & (m - 1)) == 0) {
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break;
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}
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}
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// Go from x^n to x^(n+1)
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m >>= 1;
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// Go from b(x)*x^n to b(x)*x^(n+1)
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b = (b & 1) ? ((b >> 1) ^ ISCSI_POLY) : b >> 1;
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}
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return p;
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}
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