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rbyd: Fixed ambiguous stitching alt in y-split?

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I'm not sure this is the correct solution, or why exactly we end up with
jump == branch... but the stitching alt was causing our branch-based
unflipping in the y-split logic to fail.

Changing this logic to jump >= branch seems to solve this issue, though
more investigation is needed into why...

But the good news is this small tweak solves half our current test
failures:

  test_rbyd+balance before: 300/385878 failed
  test_rbyd+balance after:  156/385878 failed (-48.0%)

Code changes:

           code          stack          ctx
  before: 38644           2624          640
  after:  38644 (+0.0%)   2624 (+0.0%)  640 (+0.0%)
This commit is contained in:
Christopher Haster
2025-01-25 13:51:29 -06:00
parent ee3a1374eb
commit 3ba17cf2f9
1 changed files with 11 additions and 6 deletions
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lfs.c
+11 -6
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@@ -3902,7 +3902,7 @@ trunk:;
if (diverging) {
// && (!lfsr_tag_isred(alt)
// || lfsr_tag_isred(p[0].alt))) {
LFS_DEBUG("%04x->%04x: div b pruning",
LFS_DEBUG("%04x->%04x: div trimming",
branch, lfsr_rbyd_eoff(rbyd));
// trim so alt is pruned
lfsr_tag_trim(
@@ -3935,7 +3935,7 @@ trunk:;
// | .-'| | .-----'
// 1 2 3 1 2 3 x
if (lfsr_tag_isred(p[0].alt)) {
LFS_DEBUG("%04x->%04x: rprune",
LFS_DEBUG("%04x->%04x: rtrim",
branch, lfsr_rbyd_eoff(rbyd));
alt = p[0].alt & ~LFSR_TAG_R;
weight = p[0].weight;
@@ -3952,7 +3952,7 @@ trunk:;
// | .-'| | .--'
// 3 4 5 3 4 5 x
} else if (!p[0].alt) { //|| lfsr_tag_isred(alt)) {
LFS_DEBUG("%04x->%04x: zprune",
LFS_DEBUG("%04x->%04x: ztrim",
branch, lfsr_rbyd_eoff(rbyd));
branch = branch_;
continue;
@@ -3966,7 +3966,7 @@ trunk:;
// .-'| .--'
// 3 4 3 4 x
} else if (!lfsr_tag_isred(alt)) {
LFS_DEBUG("%04x->%04x: bprune",
LFS_DEBUG("%04x->%04x: btrim",
branch, lfsr_rbyd_eoff(rbyd));
alt = LFSR_TAG_ALT(
LFSR_TAG_B,
@@ -4000,10 +4000,15 @@ trunk:;
// | | <b | <b |
// | | .-'| | .-'| |
// 1 2 3 4 1 2 3 4 1
if (branch_ < branch) {
if (branch_ <= branch) {
LFS_DEBUG("%04x->%04x: ysplit b",
branch, lfsr_rbyd_eoff(rbyd));
if (jump > branch) {
// TODO hwat, >= solves this??
if (jump == branch){
LFS_DEBUG("%04x->%04x: ysplit b jump == branch",
branch, lfsr_rbyd_eoff(rbyd));
}
if (jump >= branch) {
LFS_SWAP(lfsr_tag_t, &p[0].alt, &alt);
LFS_SWAP(lfsr_rid_t, &p[0].weight, &weight);
LFS_SWAP(lfs_size_t, &p[0].jump, &jump);