forked from Imagelibrary/littlefs
0f72d18b14
crc32c, with a polynomial of 0x11edc6f41, is generally numerically superior to the more common crc32 standard. Catching more bit errors across a wider range of message messages (except 2-bit errors) without any changes to the underlying algorithm. Philip Koopman has a large body of work exploring optimal polynomials here: http://users.ece.cmu.edu/~koopman/crc/crc32.html And from his experiments we know the maximum message size where we can still detect a given number of bit errors for each polynomial: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 crc32 0x104c11db7 = ∞ 4294967263 91607 2974 268 171 91 57 34 21 12 10 10 10 - - - crc32c 0x11edc6f41 = ∞ 2147483615 2147483615 5243 5243 177 177 47 47 20 20 8 8 6 6 1 1 So really crc32c should be prefered where possible. Koopman also has alternative polynomials with slightly different properties, but crc32c is already popular enough to have a decent amount of hardware support. --- Another nice feature of crc32c is that its polynomial has even parity. It turns out that even-parity polynomials give us the nifty property parity(crc(m)) == parity(m). A quick proof: crc(m) = m(x) x^|P|-1 mod P(x) parity(m) = m(x) x mod x+1 though note: x mod x+1 = 1, by hand so: parity(m) = m(x)*1 mod x+1 = m(x) mod x+1 solving for parity(crc(m)): parity(crc(m)) = (m(x) x^|P|-1 mod P(x)) mod x+1 note: (a mod b) mod c = a mod c, if c divides b, aka (a mod b) mod c = a mod c, if b mod c = 0 so if P(x) mod x+1 = 0, aka if parity(P) = 0: parity(crc(m)) = m(x) x^|P|-1 mod x+1 but, like before: x^|P|-1 mod x+1 = 1, by hand so: parity(crc(m)) = m(x)*1 mod x+1 = m(x) mod x+1 = parity(m) so if parity(P) = 0: parity(crc(m)) = parity(m) This has the potential to replace the 1-bit counter in the metadata tags with a more general solution that doesn't require extra state.
254 lines
7.2 KiB
C
254 lines
7.2 KiB
C
/*
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* lfs utility functions
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*
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* Copyright (c) 2022, The littlefs authors.
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* Copyright (c) 2017, Arm Limited. All rights reserved.
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* SPDX-License-Identifier: BSD-3-Clause
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*/
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#ifndef LFS_UTIL_H
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#define LFS_UTIL_H
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// Users can override lfs_util.h with their own configuration by defining
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// LFS_CONFIG as a header file to include (-DLFS_CONFIG=lfs_config.h).
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//
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// If LFS_CONFIG is used, none of the default utils will be emitted and must be
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// provided by the config file. To start, I would suggest copying lfs_util.h
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// and modifying as needed.
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#ifdef LFS_CONFIG
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#define LFS_STRINGIZE(x) LFS_STRINGIZE2(x)
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#define LFS_STRINGIZE2(x) #x
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#include LFS_STRINGIZE(LFS_CONFIG)
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#else
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// System includes
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#include <stdint.h>
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#include <stdbool.h>
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#include <sys/types.h>
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#include <string.h>
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#include <inttypes.h>
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#ifndef LFS_NO_MALLOC
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#include <stdlib.h>
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#endif
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#ifndef LFS_NO_ASSERT
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#include <assert.h>
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#endif
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#if !defined(LFS_NO_DEBUG) || \
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!defined(LFS_NO_WARN) || \
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!defined(LFS_NO_ERROR) || \
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defined(LFS_YES_TRACE)
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#include <stdio.h>
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#endif
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#ifdef __cplusplus
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extern "C"
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{
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#endif
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// Macros, may be replaced by system specific wrappers. Arguments to these
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// macros must not have side-effects as the macros can be removed for a smaller
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// code footprint
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// Logging functions
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#ifndef LFS_TRACE
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#ifdef LFS_YES_TRACE
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#define LFS_TRACE_(fmt, ...) \
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printf("%s:%d:trace: " fmt "%s\n", __FILE__, __LINE__, __VA_ARGS__)
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#define LFS_TRACE(...) LFS_TRACE_(__VA_ARGS__, "")
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#else
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#define LFS_TRACE(...)
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#endif
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#endif
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#ifndef LFS_DEBUG
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#ifndef LFS_NO_DEBUG
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#define LFS_DEBUG_(fmt, ...) \
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printf("%s:%d:debug: " fmt "%s\n", __FILE__, __LINE__, __VA_ARGS__)
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#define LFS_DEBUG(...) LFS_DEBUG_(__VA_ARGS__, "")
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#else
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#define LFS_DEBUG(...)
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#endif
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#endif
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#ifndef LFS_WARN
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#ifndef LFS_NO_WARN
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#define LFS_WARN_(fmt, ...) \
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printf("%s:%d:warn: " fmt "%s\n", __FILE__, __LINE__, __VA_ARGS__)
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#define LFS_WARN(...) LFS_WARN_(__VA_ARGS__, "")
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#else
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#define LFS_WARN(...)
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#endif
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#endif
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#ifndef LFS_ERROR
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#ifndef LFS_NO_ERROR
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#define LFS_ERROR_(fmt, ...) \
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printf("%s:%d:error: " fmt "%s\n", __FILE__, __LINE__, __VA_ARGS__)
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#define LFS_ERROR(...) LFS_ERROR_(__VA_ARGS__, "")
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#else
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#define LFS_ERROR(...)
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#endif
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#endif
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// Runtime assertions
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#ifndef LFS_ASSERT
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#ifndef LFS_NO_ASSERT
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#define LFS_ASSERT(test) assert(test)
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#else
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#define LFS_ASSERT(test)
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#endif
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#endif
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// Builtin functions, these may be replaced by more efficient
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// toolchain-specific implementations. LFS_NO_INTRINSICS falls back to a more
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// expensive basic C implementation for debugging purposes
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// Min/max functions for unsigned 32-bit numbers
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static inline uint32_t lfs_max(uint32_t a, uint32_t b) {
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return (a > b) ? a : b;
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}
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static inline uint32_t lfs_min(uint32_t a, uint32_t b) {
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return (a < b) ? a : b;
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}
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// Align to nearest multiple of a size
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static inline uint32_t lfs_aligndown(uint32_t a, uint32_t alignment) {
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return a - (a % alignment);
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}
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static inline uint32_t lfs_alignup(uint32_t a, uint32_t alignment) {
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return lfs_aligndown(a + alignment-1, alignment);
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}
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// Find the smallest power of 2 greater than or equal to a
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static inline uint32_t lfs_npw2(uint32_t a) {
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#if !defined(LFS_NO_INTRINSICS) && (defined(__GNUC__) || defined(__CC_ARM))
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return 32 - __builtin_clz(a-1);
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#else
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uint32_t r = 0;
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uint32_t s;
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a -= 1;
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s = (a > 0xffff) << 4; a >>= s; r |= s;
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s = (a > 0xff ) << 3; a >>= s; r |= s;
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s = (a > 0xf ) << 2; a >>= s; r |= s;
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s = (a > 0x3 ) << 1; a >>= s; r |= s;
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return (r | (a >> 1)) + 1;
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#endif
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}
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// Count the number of trailing binary zeros in a
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// lfs_ctz(0) may be undefined
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static inline uint32_t lfs_ctz(uint32_t a) {
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#if !defined(LFS_NO_INTRINSICS) && defined(__GNUC__)
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return __builtin_ctz(a);
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#else
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return lfs_npw2((a & -a) + 1) - 1;
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#endif
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}
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// Count the number of binary ones in a
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static inline uint32_t lfs_popc(uint32_t a) {
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#if !defined(LFS_NO_INTRINSICS) && (defined(__GNUC__) || defined(__CC_ARM))
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return __builtin_popcount(a);
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#else
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a = a - ((a >> 1) & 0x55555555);
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a = (a & 0x33333333) + ((a >> 2) & 0x33333333);
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return (((a + (a >> 4)) & 0xf0f0f0f) * 0x1010101) >> 24;
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#endif
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}
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// Find the sequence comparison of a and b, this is the distance
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// between a and b ignoring overflow
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static inline int lfs_scmp(uint32_t a, uint32_t b) {
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return (int)(unsigned)(a - b);
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}
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// Convert between 32-bit little-endian and native order
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static inline uint32_t lfs_fromle32(uint32_t a) {
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#if (defined( BYTE_ORDER ) && defined( ORDER_LITTLE_ENDIAN ) && BYTE_ORDER == ORDER_LITTLE_ENDIAN ) || \
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(defined(__BYTE_ORDER ) && defined(__ORDER_LITTLE_ENDIAN ) && __BYTE_ORDER == __ORDER_LITTLE_ENDIAN ) || \
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(defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
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return a;
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#elif !defined(LFS_NO_INTRINSICS) && ( \
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(defined( BYTE_ORDER ) && defined( ORDER_BIG_ENDIAN ) && BYTE_ORDER == ORDER_BIG_ENDIAN ) || \
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(defined(__BYTE_ORDER ) && defined(__ORDER_BIG_ENDIAN ) && __BYTE_ORDER == __ORDER_BIG_ENDIAN ) || \
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(defined(__BYTE_ORDER__) && defined(__ORDER_BIG_ENDIAN__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__))
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return __builtin_bswap32(a);
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#else
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return (((uint8_t*)&a)[0] << 0) |
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(((uint8_t*)&a)[1] << 8) |
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(((uint8_t*)&a)[2] << 16) |
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(((uint8_t*)&a)[3] << 24);
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#endif
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}
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static inline uint32_t lfs_tole32(uint32_t a) {
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return lfs_fromle32(a);
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}
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// Convert between 32-bit big-endian and native order
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static inline uint32_t lfs_frombe32(uint32_t a) {
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#if !defined(LFS_NO_INTRINSICS) && ( \
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(defined( BYTE_ORDER ) && defined( ORDER_LITTLE_ENDIAN ) && BYTE_ORDER == ORDER_LITTLE_ENDIAN ) || \
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(defined(__BYTE_ORDER ) && defined(__ORDER_LITTLE_ENDIAN ) && __BYTE_ORDER == __ORDER_LITTLE_ENDIAN ) || \
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(defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__))
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return __builtin_bswap32(a);
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#elif (defined( BYTE_ORDER ) && defined( ORDER_BIG_ENDIAN ) && BYTE_ORDER == ORDER_BIG_ENDIAN ) || \
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(defined(__BYTE_ORDER ) && defined(__ORDER_BIG_ENDIAN ) && __BYTE_ORDER == __ORDER_BIG_ENDIAN ) || \
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(defined(__BYTE_ORDER__) && defined(__ORDER_BIG_ENDIAN__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
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return a;
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#else
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return (((uint8_t*)&a)[0] << 24) |
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(((uint8_t*)&a)[1] << 16) |
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(((uint8_t*)&a)[2] << 8) |
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(((uint8_t*)&a)[3] << 0);
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#endif
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}
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static inline uint32_t lfs_tobe32(uint32_t a) {
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return lfs_frombe32(a);
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}
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// Calculate CRC-32 with polynomial = 0x04c11db7
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uint32_t lfs_crc(uint32_t crc, const void *buffer, size_t size);
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// Calculate crc32c incrementally
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//
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// polynomial = 0x11edc6f41
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// init = 0xffffffff
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// fini = 0xffffffff
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//
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uint32_t lfs_crc32c(uint32_t crc, const void *buffer, size_t size);
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// Allocate memory, only used if buffers are not provided to littlefs
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// Note, memory must be 64-bit aligned
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static inline void *lfs_malloc(size_t size) {
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#ifndef LFS_NO_MALLOC
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return malloc(size);
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#else
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(void)size;
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return NULL;
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#endif
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}
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// Deallocate memory, only used if buffers are not provided to littlefs
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static inline void lfs_free(void *p) {
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#ifndef LFS_NO_MALLOC
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free(p);
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#else
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(void)p;
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#endif
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}
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#ifdef __cplusplus
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} /* extern "C" */
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#endif
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#endif
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#endif
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