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Write the detect cycles function as a function to optimize code #1013

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Dec 6, 2024
Merged

Write the detect cycles function as a function to optimize code #1013

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110 changes: 56 additions & 54 deletions lfs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4396,6 +4396,30 @@ static int lfs_format_(lfs_t *lfs, const struct lfs_config *cfg) {
}
#endif

struct lfs_tortoise_t {
lfs_block_t pair[2];
lfs_size_t i;
lfs_size_t period;
};

static int lfs_tortoise_detectcycles(
const lfs_mdir_t *dir, struct lfs_tortoise_t *tortoise) {
// detect cycles with Brent's algorithm
if (lfs_pair_issync(dir->tail, tortoise->pair)) {
LFS_WARN("Cycle detected in tail list");
return LFS_ERR_CORRUPT;
}
if (tortoise->i == tortoise->period) {
tortoise->pair[0] = dir->tail[0];
tortoise->pair[1] = dir->tail[1];
tortoise->i = 0;
tortoise->period *= 2;
}
tortoise->i += 1;

return LFS_ERR_OK;
}

static int lfs_mount_(lfs_t *lfs, const struct lfs_config *cfg) {
int err = lfs_init(lfs, cfg);
if (err) {
Expand All @@ -4404,23 +4428,16 @@ static int lfs_mount_(lfs_t *lfs, const struct lfs_config *cfg) {

// scan directory blocks for superblock and any global updates
lfs_mdir_t dir = {.tail = {0, 1}};
lfs_block_t tortoise[2] = {LFS_BLOCK_NULL, LFS_BLOCK_NULL};
lfs_size_t tortoise_i = 1;
lfs_size_t tortoise_period = 1;
struct lfs_tortoise_t tortoise = {
.pair = {LFS_BLOCK_NULL, LFS_BLOCK_NULL},
.i = 1,
.period = 1,
};
while (!lfs_pair_isnull(dir.tail)) {
// detect cycles with Brent's algorithm
if (lfs_pair_issync(dir.tail, tortoise)) {
LFS_WARN("Cycle detected in tail list");
err = LFS_ERR_CORRUPT;
err = lfs_tortoise_detectcycles(&dir, &tortoise);
if (err < 0) {
goto cleanup;
}
if (tortoise_i == tortoise_period) {
tortoise[0] = dir.tail[0];
tortoise[1] = dir.tail[1];
tortoise_i = 0;
tortoise_period *= 2;
}
tortoise_i += 1;

// fetch next block in tail list
lfs_stag_t tag = lfs_dir_fetchmatch(lfs, &dir, dir.tail,
Expand Down Expand Up @@ -4633,22 +4650,17 @@ int lfs_fs_traverse_(lfs_t *lfs,
}
#endif

lfs_block_t tortoise[2] = {LFS_BLOCK_NULL, LFS_BLOCK_NULL};
lfs_size_t tortoise_i = 1;
lfs_size_t tortoise_period = 1;
struct lfs_tortoise_t tortoise = {
.pair = {LFS_BLOCK_NULL, LFS_BLOCK_NULL},
.i = 1,
.period = 1,
};
int err = LFS_ERR_OK;
while (!lfs_pair_isnull(dir.tail)) {
// detect cycles with Brent's algorithm
if (lfs_pair_issync(dir.tail, tortoise)) {
LFS_WARN("Cycle detected in tail list");
err = lfs_tortoise_detectcycles(&dir, &tortoise);
if (err < 0) {
return LFS_ERR_CORRUPT;
}
if (tortoise_i == tortoise_period) {
tortoise[0] = dir.tail[0];
tortoise[1] = dir.tail[1];
tortoise_i = 0;
tortoise_period *= 2;
}
tortoise_i += 1;

for (int i = 0; i < 2; i++) {
int err = cb(data, dir.tail[i]);
Expand Down Expand Up @@ -4727,22 +4739,17 @@ static int lfs_fs_pred(lfs_t *lfs,
// iterate over all directory directory entries
pdir->tail[0] = 0;
pdir->tail[1] = 1;
lfs_block_t tortoise[2] = {LFS_BLOCK_NULL, LFS_BLOCK_NULL};
lfs_size_t tortoise_i = 1;
lfs_size_t tortoise_period = 1;
struct lfs_tortoise_t tortoise = {
.pair = {LFS_BLOCK_NULL, LFS_BLOCK_NULL},
.i = 1,
.period = 1,
};
int err = LFS_ERR_OK;
while (!lfs_pair_isnull(pdir->tail)) {
// detect cycles with Brent's algorithm
if (lfs_pair_issync(pdir->tail, tortoise)) {
LFS_WARN("Cycle detected in tail list");
err = lfs_tortoise_detectcycles(pdir, &tortoise);
if (err < 0) {
return LFS_ERR_CORRUPT;
}
if (tortoise_i == tortoise_period) {
tortoise[0] = pdir->tail[0];
tortoise[1] = pdir->tail[1];
tortoise_i = 0;
tortoise_period *= 2;
}
tortoise_i += 1;

if (lfs_pair_cmp(pdir->tail, pair) == 0) {
return 0;
Expand Down Expand Up @@ -4792,22 +4799,17 @@ static lfs_stag_t lfs_fs_parent(lfs_t *lfs, const lfs_block_t pair[2],
// use fetchmatch with callback to find pairs
parent->tail[0] = 0;
parent->tail[1] = 1;
lfs_block_t tortoise[2] = {LFS_BLOCK_NULL, LFS_BLOCK_NULL};
lfs_size_t tortoise_i = 1;
lfs_size_t tortoise_period = 1;
struct lfs_tortoise_t tortoise = {
.pair = {LFS_BLOCK_NULL, LFS_BLOCK_NULL},
.i = 1,
.period = 1,
};
int err = LFS_ERR_OK;
while (!lfs_pair_isnull(parent->tail)) {
// detect cycles with Brent's algorithm
if (lfs_pair_issync(parent->tail, tortoise)) {
LFS_WARN("Cycle detected in tail list");
return LFS_ERR_CORRUPT;
}
if (tortoise_i == tortoise_period) {
tortoise[0] = parent->tail[0];
tortoise[1] = parent->tail[1];
tortoise_i = 0;
tortoise_period *= 2;
err = lfs_tortoise_detectcycles(parent, &tortoise);
if (err < 0) {
return err;
}
tortoise_i += 1;

lfs_stag_t tag = lfs_dir_fetchmatch(lfs, parent, parent->tail,
LFS_MKTAG(0x7ff, 0, 0x3ff),
Expand Down