I tried it on grep-2.14, and I confirmed that the patch is effective
certainly. However, I see that it's fixed in bug#17377.
$ env LC_ALL=C time -p ../grep-2.19/src/grep -E -f regex.re input_lines.txt
grep-2.14
before: real 7.66 user 7.56 sys 0.09
after : real 2.06 user 1.96 sys 0.09
grep-2.18.146-ebf3
before: real 1.59 user 1.50 sys 0.08
after : real 1.99 user 1.86 sys 0.12
If my rewriting of the patch is right, it causes slowdown rather by
building heap.
Norihiro
diff --git a/src/dfa.c b/src/dfa.c
index 3c9cb75..991b176 100644
--- a/src/dfa.c
+++ b/src/dfa.c
@@ -2073,6 +2073,133 @@ merge (position_set const *s1, position_set const *s2,
position_set * m)
m->elems[m->nelem++] = s2->elems[j++];
}
+/* Merge implementation of sorted sets, then number of sets smore than 2.
+ * Priority queue aka 'heap' data structure used to select maximum of
+ * many elements */
+
+typedef struct {
+ position p;
+ size_t set_index; /* Remember which set this element was taken from. */
+} heap_elem;
+
+static void
+heap_add (heap_elem *heap, size_t *heap_size, heap_elem e)
+{
+ size_t i = *heap_size;
+ while (i)
+ {
+ size_t parent = (i-1) / 2;
+ if (e.p.index < heap[parent].p.index)
+ break;
+
+ heap[i] = heap[parent];
+ i = parent;
+ }
+ heap[i] = e;
+ *heap_size += 1;
+}
+
+static void
+heap_remove_top_and_add (heap_elem *heap, size_t heap_size, heap_elem e)
+{
+ size_t i = 0;
+ size_t lchild = 2*i + 1;
+ size_t n = heap_size;
+ while (lchild < n)
+ {
+ size_t rchild = lchild + 1;
+ size_t nextchild = lchild;
+ if (rchild < n && heap[lchild].p.index < heap[rchild].p.index)
+ nextchild = rchild;
+ if (e.p.index >= heap[nextchild].p.index)
+ break;
+ heap[i] = heap[nextchild];
+ i = nextchild;
+ lchild = 2*i + 1;
+ }
+ heap[i] = e;
+}
+
+
+static void
+heap_remove_top (heap_elem *heap, size_t *heap_size)
+{
+ *heap_size -= 1;
+ if (*heap_size == 0)
+ return;
+ heap_remove_top_and_add (heap, *heap_size, heap[*heap_size]);
+}
+
+static void
+heap_merge_many_sets (position_set *sets, size_t n, position_set *result)
+{
+ size_t heap_size = 0;
+ position_set r; /* faster access to local variables */
+ heap_elem *heap = XNMALLOC (n, heap_elem);
+ size_t *ids = XNMALLOC (n, size_t);
+ size_t sum_of_sizes = 0;
+ size_t i;
+
+ for (i = 0; i < n; ++i)
+ {
+ sum_of_sizes += sets[i].nelem;
+ /* special value for "end of set", to reduce dependent memory
+ reads. */
+ ids[i] = ~(size_t)0;
+ if (sets[i].nelem)
+ {
+ heap_elem e = { sets[i].elems[0], i };
+ heap_add (heap, &heap_size, e);
+ if (sets[i].nelem > 1)
+ ids[i] = 1;
+ }
+ }
+
+ maybe_realloc (result->elems, sum_of_sizes, &result->alloc,
+ sizeof *result->elems);
+ r = *result;
+ r.nelem = 0;
+
+ while (heap_size)
+ {
+ heap_elem e = heap[0];
+ if (r.nelem && r.elems[r.nelem-1].index == e.p.index)
+ r.elems[r.nelem-1].constraint |= e.p.constraint;
+ else
+ r.elems[r.nelem++] = e.p;
+ i = e.set_index;
+ if (ids[i] != ~(size_t)0)
+ {
+ heap_elem e2 = { sets[i].elems[ids[i]], i };
+ heap_remove_top_and_add (heap, heap_size, e2);
+ ++ids[i];
+ if (ids[i] == sets[i].nelem)
+ ids[i] = ~(size_t)0;
+ }
+ else
+ {
+ heap_remove_top (heap, &heap_size);
+ }
+ }
+ *result = r;
+ free (ids);
+ free (heap);
+}
+
+static void
+merge_many_sets (position_set *sets, size_t n, position_set *result)
+{
+ /* optimized solutions for special/trivial cases */
+ if (n == 0)
+ result->nelem = 0;
+ else if (n == 1)
+ copy (&sets[0], result);
+ else if (n == 2)
+ merge (&sets[0], &sets[1], result);
+ else
+ heap_merge_many_sets(sets, n, result);
+}
+
/* Delete a position from a set. */
static void
delete (position p, position_set * s)
@@ -2574,6 +2701,10 @@ dfastate (state_num s, struct dfa *d, state_num trans[])
state_num state_newline; /* New state on a newline transition. */
state_num state_letter; /* New state on a letter transition. */
bool next_isnt_1st_byte = false; /* We can't add state0. */
+ position_set *sets = NULL; /* Temporary array of sets, to pass many
+ sets to merge function. */
+ size_t sets_n; /* Sets array size. */
+ size_t sets_alloc = 0; /* Sets array capacity. */
size_t i, j, k;
zeroset (matches);
@@ -2722,13 +2853,12 @@ dfastate (state_num s, struct dfa *d, state_num trans[])
for (i = 0; i < ngrps; ++i)
{
- follows.nelem = 0;
-
- /* Find the union of the follows of the positions of the group.
- This is a hideously inefficient loop. Fix it someday. */
+ /* Find the union of the follows of the positions of the group. */
+ sets_n = grps[i].nelem;
+ sets = maybe_realloc (sets, sets_n, &sets_alloc, sizeof *sets);
for (j = 0; j < grps[i].nelem; ++j)
- for (k = 0; k < d->follows[grps[i].elems[j]].nelem; ++k)
- insert (d->follows[grps[i].elems[j]].elems[k], &follows);
+ sets[j] = d->follows[grps[i].elems[j]];
+ merge_many_sets (sets, sets_n, &follows);
if (d->multibyte)
{
