Extension parser

gl_extensions.c

/* Add extension flags to the bitfield that 'flags_out' points to. 'table'
 * stores extension names and flags to check for and 'extensions' is the list
 * usually returned by the EGL or GL implementation. New flags are stored using
 * a binary OR in order to keep flags set from a previous call. Caller must
 * ensure the bitfield is set to 0 at first call.
 */
void
gl_extensions_add(const struct gl_extension_table *table,
		  const char *extensions,
		  uint64_t *flags_out)
{
	struct { const char *str; size_t len, prev, next; } *list;
	size_t i = 0, n = 0;
	uint64_t flags = 0;
	char prev_char = ' ';

	/* Get number of supported extensions. */
	while (extensions[i]) {
		if (prev_char == ' ' && extensions[i] != ' ')
			n++;
		prev_char = extensions[i++];
	}

	if (n == 0)
		return;

	/* Allocate data structure storing each supported extension string with
	 * their length. The 'prev' and 'next' members allow to skip extension
	 * strings already matched using a linked list. There's an additional
	 * entry to store the head of the list at index 0. */
	list = xmalloc((n + 1) * sizeof *list);
	list[0].prev = list[0].len = i = 0;
	list[0].next = n = 1;
	list[0].str = NULL;
	prev_char = ' ';
	while (prev_char) {
		if (extensions[i] != ' ' && extensions[i] != '\0') {
			if (prev_char == ' ')
				list[n].str = &extensions[i];
		} else if (prev_char != ' ') {
			list[n].len = &extensions[i] - list[n].str;
			list[n].prev = n - 1;
			list[n].next = n + 1;
			n++;
		}
		prev_char = extensions[i++];
	}
	list[n - 1].next = 0;

	/* Match supported extensions not yet matched with table. */
	for (; table->str && list[0].next; table++) {
		for (i = list[0].next; i; i = list[i].next) {
			if (table->len == list[i].len &&
			    !strncmp(table->str, list[i].str, table->len)) {
				list[list[i].prev].next = list[i].next;
				list[list[i].next].prev = list[i].prev;
				flags |= table->flag;
				break;
			}
		}
	}

	*flags_out |= flags;
	free(list);
}