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Grow the delete-handling deque in tre_tnfa_run_approx() dynamically #145

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Grow the delete-handling deque in tre_tnfa_run_approx() dynamically #145

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9235aba
approx: Grow the delete-handling deque dynamically
kevinushey Aug 9, 2026
d216eb2
tests: Exercise the approximate matcher with a many-branch alternation
kevinushey Aug 9, 2026
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42 changes: 36 additions & 6 deletions lib/tre-match-approx.c
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Original file line number Diff line number Diff line change
Expand Up @@ -474,8 +474,9 @@ tre_tnfa_run_approx(const tre_tnfa_t *tnfa, const void *string, ssize_t len,
pretending that all transitions are epsilon transitions, until
no more states can be reached with better costs. */
{
/* XXX - dynamic ringbuffer size */
tre_tnfa_approx_reach_t *ringbuffer[512];
int rb_size = 256;
tre_tnfa_approx_reach_t *static_ringbuffer[256];
tre_tnfa_approx_reach_t **ringbuffer = static_ringbuffer;
tre_tnfa_approx_reach_t **deque_start, **deque_end;

deque_start = deque_end = ringbuffer;
Expand All @@ -487,7 +488,34 @@ tre_tnfa_run_approx(const tre_tnfa_t *tnfa, const void *string, ssize_t len,
continue;
*deque_end = &reach_next[id];
deque_end++;
assert(deque_end != deque_start);
/* Grow the buffer (moving to the heap) if full. */
if (deque_end >= (ringbuffer + rb_size))
{
tre_tnfa_approx_reach_t **larger_buf;
size_t os = deque_start - ringbuffer;
size_t oe = deque_end - ringbuffer;
rb_size += 512;
if (ringbuffer == static_ringbuffer)
larger_buf = xmalloc(sizeof(*ringbuffer) * rb_size);
else
larger_buf = xrealloc(ringbuffer, sizeof(*ringbuffer) * rb_size);
if (larger_buf == NULL)
{
if (ringbuffer != static_ringbuffer)
xfree(ringbuffer);
#ifndef TRE_USE_ALLOCA
if (buf)
xfree(buf);
#endif /* !TRE_USE_ALLOCA */
return REG_ESPACE;
}
if (ringbuffer == static_ringbuffer)
/* Moving from stack to heap: copy existing contents. */
memcpy(larger_buf, ringbuffer, sizeof(static_ringbuffer));
ringbuffer = larger_buf;
deque_start = ringbuffer + os;
deque_end = ringbuffer + oe;
}
}

/* Repeat until the deque is empty. */
Expand Down Expand Up @@ -519,7 +547,7 @@ tre_tnfa_run_approx(const tre_tnfa_t *tnfa, const void *string, ssize_t len,
/* Too many errors or cost too large. */
DPRINT((" delete: from %03d: cost too large\n", id));
deque_start++;
if (deque_start >= (ringbuffer + 512))
if (deque_start >= (ringbuffer + rb_size))
deque_start = ringbuffer;
continue;
}
Expand Down Expand Up @@ -617,15 +645,17 @@ tre_tnfa_run_approx(const tre_tnfa_t *tnfa, const void *string, ssize_t len,
/* Add to the end of the deque. */
*deque_end = &reach_next[dest_id];
deque_end++;
if (deque_end >= (ringbuffer + 512))
if (deque_end >= (ringbuffer + rb_size))
deque_end = ringbuffer;
assert(deque_end != deque_start);
}
deque_start++;
if (deque_start >= (ringbuffer + 512))
if (deque_start >= (ringbuffer + rb_size))
deque_start = ringbuffer;
}

if (ringbuffer != static_ringbuffer)
xfree(ringbuffer);
}

#ifdef TRE_DEBUG
Expand Down
16 changes: 16 additions & 0 deletions tests/retest.c
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Original file line number Diff line number Diff line change
Expand Up @@ -625,6 +625,22 @@ main(int argc, char **argv)
test_comp("^!pfast [0-9]{1,15} ([0-9]{1,3}\\.){3}[0-9]{1,3}[0-9]{1,5}$",
REG_EXTENDED, 0);

/* An alternation with many branches. The resulting TNFA has well over
512 states reachable at one position, so the approximate matcher's
delete-handling deque must grow beyond its old fixed size (this
matters here because test_exec() also runs each test with
REG_APPROX_MATCHER). */
{
static char many_branches[600 * 5];
char *p = many_branches;
int i;
for (i = 0; i < 600; i++)
p += sprintf(p, "%sx%03d", i > 0 ? "|" : "", i);
test_comp(many_branches, REG_EXTENDED, 0);
test_exec("zzx059zz", 0, REG_OK, 2, 6, END);
test_exec("zzzzzz", 0, REG_NOMATCH);
}

#if KNOWN_BUG
/* Should these match or not? */
test_comp("(a)*-\\1b", REG_EXTENDED, 0);
Expand Down