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Merge branch 'feature' into 'main'

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remove quadratic behavior in g_string_replace

See merge request GNOME/glib!4313
This commit is contained in:
Philip Withnall
2024-09-28 21:09:53 +00:00
parent e1af498896 e8517e7776
commit 303f04286e
1 changed files with 91 additions and 17 deletions
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108
glib/gstring.c
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@@ -1023,37 +1023,111 @@ g_string_replace (GString *string,
const gchar *replace,
guint limit)
{
gsize f_len, r_len, pos;
gchar *cur, *next;
guint n = 0;
GString *new_string = NULL;
gsize f_len, r_len, new_len;
gchar *cur, *next, *first, *dst;
guint n;
g_return_val_if_fail (string != NULL, 0);
g_return_val_if_fail (find != NULL, 0);
g_return_val_if_fail (replace != NULL, 0);
first = strstr (string->str, find);
if (first == NULL)
return 0;
new_len = string->len;
f_len = strlen (find);
r_len = strlen (replace);
cur = string->str;
while ((next = strstr (cur, find)) != NULL)
/* Potentially do two passes: the first to calculate the length of the new string,
* new_len, if it’s going to be longer than the original string; and the second to
* do the replacements. The first pass is skipped if the new string is going to be
* no longer than the original. */
do
{
pos = next - string->str;
g_string_erase (string, pos, f_len);
g_string_insert (string, pos, replace);
cur = string->str + pos + r_len;
n++;
/* Only match the empty string once at any given position, to
* avoid infinite loops */
if (f_len == 0)
dst = first;
cur = first;
n = 0;
while ((next = strstr (cur, find)) != NULL)
{
if (cur[0] == '\0')
break;
n++;
if G_UNLIKELY (f_len == 0)
{
g_string_insert_len (string, next - string->str, replace, r_len);
cur = next + r_len;
/* Only match the empty string once at any given position, to
* avoid infinite loops */
if (cur[0] == '\0')
break;
else
cur++;
}
else
cur++;
{
if (r_len <= f_len)
{
memmove (dst, cur, next - cur);
dst += next - cur;
memcpy (dst, replace, r_len);
dst += r_len;
}
else
{
if (new_string == NULL)
{
new_len += r_len - f_len;
}
else
{
g_string_append_len (new_string, cur, next - cur);
g_string_append_len (new_string, replace, r_len);
}
}
cur = next + f_len;
}
if (n == limit)
break;
}
if (n == limit)
/* @find is an empty string. */
if (f_len == 0)
break;
/* Append the trailing characters from after the final instance of @find
* in the input string. */
if (r_len <= f_len)
{
/* First pass skipped. */
gchar *end = string->str + string->len;
memmove (dst, cur, end - cur);
end = dst + (end - cur);
*end = 0;
string->len = end - string->str;
break;
}
else
{
if (new_string == NULL)
{
/* First pass. */
new_string = g_string_sized_new (new_len);
g_string_append_len (new_string, string->str, first - string->str);
}
else
{
/* Second pass. */
g_string_append_len (new_string, cur, (string->str + string->len) - cur);
g_free (string->str);
string->allocated_len = new_string->allocated_len;
string->len = new_string->len;
string->str = g_string_free_and_steal (g_steal_pointer (&new_string));
break;
}
}
}
while (1);
return n;
}