mirror of
https://github.com/eledio-devices/thirdparty-littlefs.git
synced 2025-10-31 16:14:16 +01:00
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
/*
|
|
* lfs utility functions
|
|
*
|
|
* Copyright (c) 2017 ARM Limited
|
|
*
|
|
* Licensed under the Apache License, Version 2.0 (the "License");
|
|
* you may not use this file except in compliance with the License.
|
|
* You may obtain a copy of the License at
|
|
*
|
|
* http://www.apache.org/licenses/LICENSE-2.0
|
|
*
|
|
* Unless required by applicable law or agreed to in writing, software
|
|
* distributed under the License is distributed on an "AS IS" BASIS,
|
|
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
* See the License for the specific language governing permissions and
|
|
* limitations under the License.
|
|
*/
|
|
#ifndef LFS_UTIL_H
|
|
#define LFS_UTIL_H
|
|
|
|
#include <stdlib.h>
|
|
#include <stdint.h>
|
|
#include <stdio.h>
|
|
|
|
|
|
// Builtin functions, these may be replaced by more
|
|
// efficient implementations in the system
|
|
static inline uint32_t lfs_max(uint32_t a, uint32_t b) {
|
|
return (a > b) ? a : b;
|
|
}
|
|
|
|
static inline uint32_t lfs_min(uint32_t a, uint32_t b) {
|
|
return (a < b) ? a : b;
|
|
}
|
|
|
|
static inline uint32_t lfs_ctz(uint32_t a) {
|
|
return __builtin_ctz(a);
|
|
}
|
|
|
|
static inline uint32_t lfs_npw2(uint32_t a) {
|
|
return 32 - __builtin_clz(a-1);
|
|
}
|
|
|
|
static inline uint32_t lfs_popc(uint32_t a) {
|
|
return __builtin_popcount(a);
|
|
}
|
|
|
|
static inline int lfs_scmp(uint32_t a, uint32_t b) {
|
|
return (int)(unsigned)(a - b);
|
|
}
|
|
|
|
// CRC-32 with polynomial = 0x04c11db7
|
|
void lfs_crc(uint32_t *crc, const void *buffer, size_t size);
|
|
|
|
|
|
// Logging functions, these may be replaced by system-specific
|
|
// logging functions
|
|
#define LFS_DEBUG(fmt, ...) printf("lfs debug: " fmt "\n", __VA_ARGS__)
|
|
#define LFS_WARN(fmt, ...) printf("lfs warn: " fmt "\n", __VA_ARGS__)
|
|
#define LFS_ERROR(fmt, ...) printf("lfs error: " fmt "\n", __VA_ARGS__)
|
|
|
|
|
|
#endif
|