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https://github.com/eledio-devices/thirdparty-littlefs.git
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46e22b2a38
This reduces the O(n^2logn) runtime to read a file to only O(nlog). The extra O(n) did not touch the disk, so it isn't a problem until the files become very large, but this solution comes with very little cost. Long story short, you can find the block index + offset pair for a CTZ linked-list with this series of formulas: n' = floor(N / (B - 2w/8)) N' = (B - 2w/8)n' + (w/8)popcount(n') off' = N - N' n, off = n'-1, off'+B if off' < 0 n', off'+(w/8)(ctz(n')+1) if off' >= 0 For the long story, you will need to see the updated DESIGN.md
64 lines
1.7 KiB
C
64 lines
1.7 KiB
C
/*
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* lfs utility functions
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*
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* Copyright (c) 2017 ARM Limited
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef LFS_UTIL_H
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#define LFS_UTIL_H
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#include <stdlib.h>
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#include <stdint.h>
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#include <stdio.h>
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// Builtin functions, these may be replaced by more
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// efficient implementations in the system
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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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static inline uint32_t lfs_ctz(uint32_t a) {
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return __builtin_ctz(a);
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}
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static inline uint32_t lfs_npw2(uint32_t a) {
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return 32 - __builtin_clz(a-1);
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}
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static inline uint32_t lfs_popc(uint32_t a) {
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return __builtin_popcount(a);
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}
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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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// CRC-32 with polynomial = 0x04c11db7
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void lfs_crc(uint32_t *crc, const void *buffer, size_t size);
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// Logging functions, these may be replaced by system-specific
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// logging functions
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#define LFS_DEBUG(fmt, ...) printf("lfs debug: " fmt "\n", __VA_ARGS__)
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#define LFS_WARN(fmt, ...) printf("lfs warn: " fmt "\n", __VA_ARGS__)
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#define LFS_ERROR(fmt, ...) printf("lfs error: " fmt "\n", __VA_ARGS__)
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#endif
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