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Implement RtlListLoop() routine for detecting loops in linked lists

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This commit is contained in:
Rafal Kupiec 2022-09-27 19:30:19 +02:00
parent bf9171b66a
commit 6c6e5fe70a
Signed by: belliash
GPG Key ID: 4E829243E0CFE6B4
1 changed files with 48 additions and 3 deletions
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51
xtoskrnl/rtl/plist.c
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@ -44,7 +44,7 @@ RtlInitializeListHead32(IN PLIST_ENTRY32 ListHead)
} }
/** /**
* This routine inserts an entry at the head of a double linked list. * This routine inserts an entry at the head of a doubly linked list.
* *
* @param ListHead * @param ListHead
* Pointer to the head of the list. * Pointer to the head of the list.
@ -67,7 +67,7 @@ RtlInsertHeadList(IN OUT PLIST_ENTRY ListHead,
} }
/** /**
* This routine inserts an entry at the tail of a double linked list. * This routine inserts an entry at the tail of a doubly linked list.
* *
* @param ListHead * @param ListHead
* Pointer to the head of the list. * Pointer to the head of the list.
@ -90,7 +90,7 @@ RtlInsertTailList(IN OUT PLIST_ENTRY ListHead,
} }
/** /**
* Indicates whether a double linked list structure is empty. * Indicates whether a doubly linked list structure is empty.
* *
* @param ListHead * @param ListHead
* Pointer to a structure that represents the head of the list. * Pointer to a structure that represents the head of the list.
@ -104,3 +104,48 @@ RtlListEmpty(PLIST_ENTRY ListHead)
{ {
return (ListHead->Flink == ListHead); return (ListHead->Flink == ListHead);
} }
/**
* This routine detects a loop in a doubly linked list.
*
* @param ListHead
* Pointer to a structure that represents the head of the list.
*
* @return TRUE if linked list contains a loop or FALSE otherwise.
*
* @since XT 1.0
*/
BOOLEAN
RtlListLoop(PLIST_ENTRY ListHead)
{
PLIST_ENTRY SlowEntry, FastEntry;
/* Check if list exists */
if(ListHead == NULL)
{
/* No loop in non-existen list */
return FALSE;
}
/* Make both references pointing to the start of the list */
FastEntry = ListHead;
SlowEntry = ListHead;
/* Iterate through the linked list to find a loop */
while(SlowEntry != NULL && FastEntry != NULL && FastEntry->Flink != NULL)
{
/* Move slow and fast pointers by one and two positions accordingly */
SlowEntry = SlowEntry->Flink;
FastEntry = FastEntry->Flink->Flink;
/* Compare both pointers */
if(SlowEntry == FastEntry)
{
/* Loop found */
return TRUE;
}
}
/* No loop found */
return FALSE;
}