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timsort: add ELEM_REV()

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for reverse-element lookup.

Because our indices are always unsigned, we need to take special care
to not trigger compiler warnings when doing negative array indexing.

And yes, for now "0 - x" is good enough.
This commit is contained in:
Benjamin Otte
2024-10-21 06:57:45 +02:00
parent 516506e1ad
commit 5a6ea4ac86
1 changed files with 14 additions and 13 deletions
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27
gtk/timsort/gtktimsort-impl.c
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@@ -25,6 +25,7 @@
#define INCPTR(x) ((gpointer) ((char *) (x) + WIDTH))
#define DECPTR(x) ((gpointer) ((char *) (x) - WIDTH))
#define ELEM(a, i) ((char *) (a) + (i) * WIDTH)
#define ELEM_REV(a, i) ELEM(a, 0 - (i))
#define LEN(n) ((n) * WIDTH)
#define CONCAT(x, y) gtk_tim_sort_ ## x ## _ ## y
@@ -296,7 +297,7 @@ gtk_tim_sort(gallop_left) (GtkTimSort *self,
const gsize max_ofs = hint + 1;
gsize tmp;
while (ofs < max_ofs
&& gtk_tim_sort_compare (self, key, ELEM (hintp, -ofs)) <= 0)
&& gtk_tim_sort_compare (self, key, ELEM_REV (hintp, ofs)) <= 0)
{
last_ofs = ofs;
ofs = (ofs << 1) + 1; /* no need to check for overflow */
@@ -363,7 +364,7 @@ gtk_tim_sort(gallop_right) (GtkTimSort *self,
gsize max_ofs = hint + 1;
gsize tmp;
while (ofs < max_ofs
&& gtk_tim_sort_compare (self, key, ELEM (hintp, -ofs)) < 0)
&& gtk_tim_sort_compare (self, key, ELEM_REV (hintp, ofs)) < 0)
{
last_ofs = ofs;
ofs = (ofs << 1) + 1; /* no need to check for overflow */
@@ -622,13 +623,13 @@ gtk_tim_sort(merge_hi) (GtkTimSort *self,
cursor1 = DECPTR (cursor1);
if (--len1 == 0)
{
memcpy (ELEM (dest, -(len2 - 1)), tmp, LEN (len2)); /* POP: can't overlap */
memcpy (ELEM_REV (dest, (len2 - 1)), tmp, LEN (len2)); /* POP: can't overlap */
return;
}
if (len2 == 1)
{
dest = ELEM (dest, -len1);
cursor1 = ELEM (cursor1, -len1);
dest = ELEM_REV (dest, len1);
cursor1 = ELEM_REV (cursor1, len1);
memmove (ELEM (dest, 1), ELEM (cursor1, 1), LEN (len1)); /* POP: overlaps */
/* a[dest] = tmp[cursor2]; */
ASSIGN (dest, cursor2);
@@ -684,8 +685,8 @@ gtk_tim_sort(merge_hi) (GtkTimSort *self,
count1 = len1 - gtk_tim_sort(gallop_right) (self, cursor2, base1, len1, len1 - 1);
if (count1 != 0)
{
dest = ELEM (dest, -count1);
cursor1 = ELEM (cursor1, -count1);
dest = ELEM_REV (dest, count1);
cursor1 = ELEM_REV (cursor1, count1);
len1 -= count1;
memmove (INCPTR (dest), INCPTR (cursor1),
LEN (count1)); /* POP: might overlap */
@@ -701,8 +702,8 @@ gtk_tim_sort(merge_hi) (GtkTimSort *self,
count2 = len2 - gtk_tim_sort(gallop_left) (self, cursor1, tmp, len2, len2 - 1);
if (count2 != 0)
{
dest = ELEM (dest, -count2);
cursor2 = ELEM (cursor2, -count2);
dest = ELEM_REV (dest, count2);
cursor2 = ELEM_REV (cursor2, count2);
len2 -= count2;
memcpy (INCPTR (dest), INCPTR (cursor2), LEN (count2)); /* POP: can't overlap */
if (len2 <= 1) /* len2 == 1 || len2 == 0 */
@@ -725,8 +726,8 @@ outer:
if (len2 == 1)
{
g_assert (len1 > 0);
dest = ELEM (dest, -len1);
cursor1 = ELEM (cursor1, -len1);
dest = ELEM_REV (dest, len1);
cursor1 = ELEM_REV (cursor1, len1);
memmove (INCPTR (dest), INCPTR (cursor1), LEN (len1)); /* POP: might overlap */
/* a[dest] = tmp[cursor2]; // Move first elt of run2 to front of merge */
ASSIGN (dest, cursor2);
@@ -740,7 +741,7 @@ outer:
{
g_assert (len1 == 0);
g_assert (len2 > 0);
memcpy (ELEM (dest, -(len2 - 1)), tmp, LEN (len2)); /* POP: can't overlap */
memcpy (ELEM_REV (dest, (len2 - 1)), tmp, LEN (len2)); /* POP: can't overlap */
}
}
@@ -802,7 +803,7 @@ gtk_tim_sort(merge_at) (GtkTimSort *self,
gtk_tim_sort(merge_lo) (self, base1, self->max_merge_size, base2, len2);
gtk_tim_sort_set_change (out_change, base1, self->max_merge_size + len2);
self->run[i].len -= self->max_merge_size;
self->run[i + 1].base = ELEM (self->run[i + 1].base, - self->max_merge_size);
self->run[i + 1].base = ELEM_REV (self->run[i + 1].base, self->max_merge_size);
self->run[i + 1].len += self->max_merge_size;
g_assert (ELEM (self->run[i].base, self->run[i].len) == self->run[i + 1].base);
return;