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Simplified the diverged state machine in lfsr_rbyd_appendattr

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Just made d_pruned its own variable. Encoding d_pruned into the state
machine is overkill.

We're not on the hot-path, so stack usage is not a premium, and even if
we were this is a single bool that could probably fit in some padding
somewhere. And the compiler is going to likely be better at optimizing
with a simpler encoding.

Code changes:

           code          stack
  before: 33988           2864
  after:  33968 (+0.0%)   2864 (+0.0%)
This commit is contained in:
Christopher Haster
2024-03-21 13:20:45 -05:00
parent 531c2bcc4c
commit 16ca642508
1 changed files with 16 additions and 42 deletions
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lfs.c
+16 -42
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@@ -2693,46 +2693,21 @@ static void lfsr_rbyd_p_recolor(
// diverged state machine for range appends
enum {
LFSR_D_NOTDIVERGING = 0x0,
LFSR_D_DIVERGINGLOWER = 0x2,
LFSR_D_DIVERGINGUPPER = 0x3,
LFSR_D_DIVERGEDLOWER = 0x4,
LFSR_D_DIVERGEDUPPER = 0x5,
LFSR_D_PRUNEDLOWER = 0x6,
LFSR_D_PRUNEDUPPER = 0x7,
LFSR_D_NOTDIVERGING = 0,
LFSR_D_DIVERGINGLOWER = 1,
LFSR_D_DIVERGINGUPPER = 2,
LFSR_D_DIVERGEDLOWER = 3,
LFSR_D_DIVERGEDUPPER = 4,
};
static inline bool lfsr_d_isdiverged(uint8_t d_state) {
return d_state >= LFSR_D_DIVERGEDLOWER;
}
static inline bool lfsr_d_isupper(uint8_t d_state) {
return d_state & 0x1;
}
static inline bool lfsr_d_islower(uint8_t d_state) {
return !(d_state & 0x1);
}
static inline bool lfsr_d_ispruned(uint8_t d_state) {
return d_state >= LFSR_D_PRUNEDLOWER;
}
static inline uint8_t lfsr_d_diverge(uint8_t d_state) {
LFS_ASSERT(d_state != LFSR_D_NOTDIVERGING);
return (!lfsr_d_isdiverged(d_state))
? d_state + (LFSR_D_DIVERGEDLOWER - LFSR_D_DIVERGINGLOWER)
: d_state;
}
static inline uint8_t lfsr_d_prune(uint8_t d_state) {
LFS_ASSERT(lfsr_d_isdiverged(d_state));
return d_state | 0x2;
}
static inline uint8_t lfsr_d_unprune(uint8_t d_state) {
LFS_ASSERT(lfsr_d_isdiverged(d_state));
return d_state & ~0x2;
LFS_ASSERT(!lfsr_d_isdiverged(d_state));
return d_state + (LFSR_D_DIVERGEDLOWER - LFSR_D_DIVERGINGLOWER);
}
// core rbyd algorithm
@@ -2825,6 +2800,7 @@ static int lfsr_rbyd_appendattr(lfs_t *lfs, lfsr_rbyd_t *rbyd,
uint8_t d_state = (a_rid != b_rid || a_tag != b_tag)
? LFSR_D_DIVERGINGLOWER
: LFSR_D_NOTDIVERGING;
bool d_pruned = false;
lfs_size_t d_branch = rbyd->eoff;
lfsr_tag_t d_tag = 0;
lfsr_srid_t d_rid = 0;
@@ -2904,7 +2880,7 @@ again:;
d_state = lfsr_d_diverge(d_state);
// stitch together diverged branches
if (lfsr_d_isupper(d_state) && d_tag) {
if (d_state == LFSR_D_DIVERGEDUPPER && d_tag) {
err = lfsr_rbyd_p_push(lfs, rbyd,
p_alts, p_weights, p_jumps,
LFSR_TAG_ALT(LFSR_TAG_LE, LFSR_TAG_B, d_tag),
@@ -2935,7 +2911,7 @@ again:;
// prune because of diverged paths?
|| d_state == LFSR_D_DIVERGINGLOWER
|| (lfsr_d_isdiverged(d_state)
&& lfsr_d_isupper(d_state)
&& (d_state == LFSR_D_DIVERGEDUPPER)
^ lfsr_tag_isgt(alt)
^ lfsr_tag_follow2(
alt, weight,
@@ -2969,7 +2945,7 @@ again:;
// propagate pruning to yellow splits to avoid issues
// with tail-recursive recoloring
if (lfsr_d_isdiverged(d_state)) {
d_state = lfsr_d_prune(d_state);
d_pruned = true;
}
y_branch = branch;
branch = branch_;
@@ -3010,7 +2986,7 @@ again:;
&lower_rid, &upper_rid,
&lower_tag, &upper_tag);
p_alts[0] &= ~LFSR_TAG_R;
if (!lfsr_d_ispruned(d_state)) {
if (!d_pruned) {
lfsr_rbyd_p_recolor(p_alts, p_weights, p_jumps);
}
@@ -3036,7 +3012,7 @@ again:;
&lower_rid, &upper_rid,
&lower_tag, &upper_tag);
p_alts[0] &= ~LFSR_TAG_R;
if (!lfsr_d_ispruned(d_state)) {
if (!d_pruned) {
lfsr_rbyd_p_recolor(p_alts, p_weights, p_jumps);
}
@@ -3091,9 +3067,7 @@ again:;
&lower_rid, &upper_rid,
&lower_tag, &upper_tag);
// no longer pruned
if (lfsr_d_isdiverged(d_state)) {
d_state = lfsr_d_unprune(d_state);
}
d_pruned = false;
}
// push alt onto our queue
@@ -3126,7 +3100,7 @@ again:;
goto again;
// diverged lower trunk? we need an upper trunk too
} else if (lfsr_d_isdiverged(d_state) && lfsr_d_islower(d_state)) {
} else if (d_state == LFSR_D_DIVERGEDLOWER) {
// keep track of last alt on diverged trunk to stitch the trunks
// together with
d_state = LFSR_D_DIVERGINGUPPER;
@@ -3158,7 +3132,7 @@ again:;
goto again;
// diverged upper trunk? done diverging
} else if (lfsr_d_isdiverged(d_state) && lfsr_d_isupper(d_state)) {
} else if (d_state == LFSR_D_DIVERGEDUPPER) {
// use the diverged rid bound for leaf weight calculation
lower_rid = d_rid;
}