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https://github.com/XTXMarkets/ternfs.git
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136d55bff0
Specifically:
* Extend tables so that they won't wrap around wrongly for big sizes
(we would never hit this since our blocks are at most a few MBs
big).
* Use CRC instructions to compute remainders.
56 lines
1.8 KiB
C
56 lines
1.8 KiB
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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// Computes the CRC32C (C = "Castagnoli" polynomial, also used in iSCSI)
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//
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// As usual, the CRC is initialized with -1, and xor'd with -1 at the end.
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// Since we provide `crc32c` so that the CRC can be computed incrementally,
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// we just invert the crc at the beginning and at the end.
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//
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// See <https://en.wikipedia.org/wiki/Computation_of_cyclic_redundancy_checks#CRC_variants>.
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//
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// The pclmul versions use pclmul instructions, and are therefore generally faster. They're
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// otherwise identical to the non-pclmul versions.
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#ifndef TERN_CRC32C
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#define TERN_CRC32C
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#include <stdint.h>
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#include <sys/types.h>
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#ifdef __cplusplus
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extern "C" {
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#endif
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// Initialize crc with 0.
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uint32_t crc32c(uint32_t crc, const char* buf, size_t len);
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// Computes the CRC32C of the XOR between two equally long
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// strings, given their crcs and their length.
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uint32_t crc32c_xor(uint32_t crc1, uint32_t crc2, size_t len);
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// Computes the CRC32C of the concatenation of two strings, given
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// their crcs and the length of the second string.
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uint32_t crc32c_append(uint32_t crc1, uint32_t crc2, size_t len2);
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// Computes the CRC32C that you'd get by doing
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//
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// char* zero_bytes = (char*)malloc(zeros);
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// memset(zero_bytes, 0, zeros);
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// crc = crc32c(crc, zero_bytes, zeros);
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//
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// `zeros` can be negative, in which case this "undoes" `zeros`
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// zeroes.
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uint32_t crc32c_zero_extend(uint32_t crc, ssize_t zeros);
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uint32_t crc32c_pclmul(uint32_t crc, const char* buf, size_t len);
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uint32_t crc32c_xor_pclmul(uint32_t crc1, uint32_t crc2, size_t len);
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uint32_t crc32c_append_pclmul(uint32_t crc1, uint32_t crc2, size_t len2);
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uint32_t crc32c_zero_extend_pclmul(uint32_t crc, ssize_t zeros);
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#ifdef __cplusplus
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}
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#endif
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#endif
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