Github/littlefs
1
Fork 0
Code Actions Activity

Replaced lfs->seed with lfs->gcksum for pseudorandom noise

Browse Source 
lfs->seed was already just the rough xor of all mdir cksums, so
replacing it with our gcksum doesn't really do anything but make its
definition more rigorous.

That and save both code and ctx:

           code          stack          ctx
  before: 38560           2624          644
  after:  38492 (-0.2%)   2624 (+0.0%)  640 (-0.6%)
This commit is contained in:
Christopher Haster
2025-01-18 02:35:16 -06:00
parent c86f3bda00
commit 8cfaacbfb6
2 changed files with 3 additions and 17 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lfs.c
+3 -16
View File
@@ -7044,7 +7044,7 @@ static inline uint32_t lfsr_rev_init(lfs_t *lfs, uint32_t rev) {
// increment revision // increment revision
rev += 1 << 28; rev += 1 << 28;
// xor in a pseudorandom nonce // xor in a pseudorandom nonce
rev ^= ((1 << (28-lfs_smax(lfs->recycle_bits, 0)))-1) & lfs->seed; rev ^= ((1 << (28-lfs_smax(lfs->recycle_bits, 0)))-1) & lfs->gcksum;
return rev; return rev;
} }
@@ -7062,7 +7062,7 @@ static inline uint32_t lfsr_rev_inc(lfs_t *lfs, uint32_t rev) {
// increment recycle counter/revision // increment recycle counter/revision
rev += 1 << (28-lfs_smax(lfs->recycle_bits, 0)); rev += 1 << (28-lfs_smax(lfs->recycle_bits, 0));
// xor in a pseudorandom nonce // xor in a pseudorandom nonce
rev ^= ((1 << (28-lfs_smax(lfs->recycle_bits, 0)))-1) & lfs->seed; rev ^= ((1 << (28-lfs_smax(lfs->recycle_bits, 0)))-1) & lfs->gcksum;
return rev; return rev;
} }
@@ -8751,14 +8751,6 @@ static int lfsr_mdir_commit(lfs_t *lfs, lfsr_mdir_t *mdir,
// success? update in-device state, we must not error at this point! // // success? update in-device state, we must not error at this point! //
/////////////////////////////////////////////////////////////////////// ///////////////////////////////////////////////////////////////////////
// toss our cksum into the filesystem seed for pseudorandom numbers
if (mdelta >= 0) {
lfs->seed ^= mdir_[0].rbyd.cksum;
}
if (mdelta > 0) {
lfs->seed ^= mdir_[1].rbyd.cksum;
}
// we may have touched any number of mdirs, so assume uncompacted // we may have touched any number of mdirs, so assume uncompacted
// until lfsr_gc can prove otherwise // until lfsr_gc can prove otherwise
lfs->flags |= LFS_I_COMPACT; lfs->flags |= LFS_I_COMPACT;
@@ -13384,7 +13376,6 @@ static int lfs_init(lfs_t *lfs, uint32_t flags,
} }
// setup default state // setup default state
lfs->seed = 0;
// lfs->root[0] = LFS_BLOCK_NULL; // lfs->root[0] = LFS_BLOCK_NULL;
// lfs->root[1] = LFS_BLOCK_NULL; // lfs->root[1] = LFS_BLOCK_NULL;
@@ -13959,10 +13950,6 @@ static int lfsr_mountinited(lfs_t *lfs) {
} }
} }
// toss our cksum into the filesystem seed for pseudorandom
// numbers
lfs->seed ^= mdir->rbyd.cksum;
// build gcksum out of mdir cksums // build gcksum out of mdir cksums
lfs->gcksum ^= mdir->rbyd.cksum; lfs->gcksum ^= mdir->rbyd.cksum;
@@ -14027,7 +14014,7 @@ static int lfsr_mountinited(lfs_t *lfs) {
// the purpose of this is to avoid bad wear patterns such as always // the purpose of this is to avoid bad wear patterns such as always
// allocating blocks near the beginning of disk after a power-loss // allocating blocks near the beginning of disk after a power-loss
// //
lfs->lookahead.window = lfs->seed % lfs->block_count; lfs->lookahead.window = lfs->gcksum % lfs->block_count;
// TODO should the consumegdelta above take gstate/gdelta as a parameter? // TODO should the consumegdelta above take gstate/gdelta as a parameter?
// keep track of the current gstate on disk // keep track of the current gstate on disk
lfs.h
-1
View File
@@ -850,7 +850,6 @@ typedef struct lfs {
lfsr_mdir_t mroot; lfsr_mdir_t mroot;
lfsr_mtree_t mtree; lfsr_mtree_t mtree;
uint32_t seed;
struct { struct {
lfs_block_t block; lfs_block_t block;