From 8cfaacbfb6f16379199ab810561f188a213243b3 Mon Sep 17 00:00:00 2001
From: Christopher Haster <geky@geky.net>
Date: Sat, 18 Jan 2025 02:35:16 -0600
Subject: [PATCH] Replaced lfs->seed with lfs->gcksum for pseudorandom noise

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%)
---
 lfs.c | 19 +++----------------
 lfs.h |  1 -
 2 files changed, 3 insertions(+), 17 deletions(-)

diff --git a/lfs.c b/lfs.c
index a355bdee..a87b7764 100644
--- a/lfs.c
+++ b/lfs.c
@@ -7044,7 +7044,7 @@ static inline uint32_t lfsr_rev_init(lfs_t *lfs, uint32_t rev) {
     // increment revision
     rev += 1 << 28;
     // 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;
 }
 
@@ -7062,7 +7062,7 @@ static inline uint32_t lfsr_rev_inc(lfs_t *lfs, uint32_t rev) {
     // increment recycle counter/revision
     rev += 1 << (28-lfs_smax(lfs->recycle_bits, 0));
     // 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;
 }
 
@@ -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! //
     ///////////////////////////////////////////////////////////////////////
 
-    // 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
     // until lfsr_gc can prove otherwise
     lfs->flags |= LFS_I_COMPACT;
@@ -13384,7 +13376,6 @@ static int lfs_init(lfs_t *lfs, uint32_t flags,
     }
 
     // setup default state
-    lfs->seed = 0;
 
 //    lfs->root[0] = 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
             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 
     // 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?
     // keep track of the current gstate on disk
diff --git a/lfs.h b/lfs.h
index 5818902c..621459d3 100644
--- a/lfs.h
+++ b/lfs.h
@@ -850,7 +850,6 @@ typedef struct lfs {
 
     lfsr_mdir_t mroot;
     lfsr_mtree_t mtree;
-    uint32_t seed;
 
     struct {
         lfs_block_t block;