forked from Imagelibrary/littlefs
546fff77fb
The main motivation for this was issues fitting a good tag encoding into
14-bits. The extra 2-bits (though really only 1 bit was needed) from
making this not a leb encoding opens up the space from 3 suptypes to
15 suptypes, which is nothing to shake a stick at.
The main downsides:
1. We can't rely on leb encoding for effectively-infinite extensions.
2. We can't shorten small tags (crcs, grows, shrinks) to one byte.
For 1., extending the leb encoding beyond 14-bits is already
unpalatable, because it would increase RAM costs in the tag
encoder/decoder,` which must assume a worst-case tag size, and would likely
add storage cost to every alt pointer, more on this in the next section.
The current encoding is quite generous, so I think it is unlikely we
will exceed the 16-bit encoding space. But even if we do, it's possible
to use a spare bit for an "extended" set of tags in the future.
As for 2., the lack of compression is a downside, but I've realized the
only tags that really matter storage-wise are the alt pointers. In any
rbyds there will be roughly O(m log m) alt pointers, but at most O(m) of
any other tags. What this means is that the encoding of any other tag is
in the noise of the encoding of our alt pointers.
Our alt pointers are already pretty densely packed. But because the
sparse key part of alt-pointers are stored as-is, the worst-case
encoding of in-tree tags likely ends up as the encoding of our
alt-pointers. So going up to 3-byte tags adds a surprisingly large
storage cost.
As a minor plus, le16s should be slightly cheaper to encode/decode. It
should also be slightly easier to debug tags on-disk.
tag encoding:
TTTTtttt ttttTTTv
^--------^--^^- 4+3-bit suptype
'---|- 8-bit subtype
'- valid bit
iiii iiiiiii iiiiiii iiiiiii iiiiiii
^- m-bit id/weight
llll lllllll lllllll lllllll lllllll
^- m-bit length/jump
Also renamed the "mk" tags, since they no longer have special behavior
outside of providing names for entries:
- LFSR_TAG_MK => LFSR_TAG_NAME
- LFSR_TAG_MKBRANCH => LFSR_TAG_BNAME
- LFSR_TAG_MKREG => LFSR_TAG_REG
- LFSR_TAG_MKDIR => LFSR_TAG_DIR
337 lines
9.3 KiB
C
337 lines
9.3 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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static inline uint32_t lfs_max32(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_min32(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 int32_t lfs_smax32(int32_t a, int32_t b) {
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return (a > b) ? a : b;
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}
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static inline int32_t lfs_smin32(int32_t a, int32_t b) {
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return (a < b) ? a : b;
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}
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// TODO how many of these do we actually need
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// Swap two 16-bit numbers
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static inline void lfs_swap16(uint16_t *a, uint16_t *b) {
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uint16_t t = *a;
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*a = *b;
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*b = t;
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}
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static inline void lfs_sswap16(int16_t *a, int16_t *b) {
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int16_t t = *a;
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*a = *b;
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*b = t;
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}
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// Swap two 32-bit numbers
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static inline void lfs_swap32(uint32_t *a, uint32_t *b) {
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uint32_t t = *a;
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*a = *b;
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*b = t;
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}
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static inline void lfs_sswap32(int32_t *a, int32_t *b) {
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int32_t t = *a;
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*a = *b;
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*b = t;
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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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// TODO we should eventually adopt this as the new name for npw2
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// Find the ceiling of log base 2 of the given number
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static inline uint32_t lfs_nlog2(uint32_t a) {
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return lfs_npw2(a);
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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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// Convert to/from 16-bit little-endian
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static inline void lfs_tole16_(uint16_t word, void *buffer) {
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((uint8_t*)buffer)[0] = word >> 0;
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((uint8_t*)buffer)[1] = word >> 8;
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}
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static inline uint16_t lfs_fromle16_(const void *buffer) {
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return (((uint8_t*)buffer)[0] << 0)
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| (((uint8_t*)buffer)[1] << 8);
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}
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// Convert to/from 32-bit little-endian
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static inline void lfs_tole32_(uint32_t word, void *buffer) {
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((uint8_t*)buffer)[0] = word >> 0;
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((uint8_t*)buffer)[1] = word >> 8;
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((uint8_t*)buffer)[2] = word >> 16;
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((uint8_t*)buffer)[3] = word >> 24;
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}
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static inline uint32_t lfs_fromle32_(const void *buffer) {
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return (((uint8_t*)buffer)[0] << 0)
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| (((uint8_t*)buffer)[1] << 8)
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| (((uint8_t*)buffer)[2] << 16)
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| (((uint8_t*)buffer)[3] << 24);
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}
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// Convert to/from leb128 encoding
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// TODO should we really be using ssize_t here and not lfs_ssize_t?
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ssize_t lfs_toleb128(uint32_t word, void *buffer, size_t size);
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ssize_t lfs_fromleb128(uint32_t *word, const void *buffer, size_t size);
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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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