ReactOS 0.4.15-dev-8222-g9164419
skiplist.c File Reference
#include <intrin.h>
#include <windef.h>
#include <winbase.h>
#include "skiplist.h"
Include dependency graph for skiplist.c:

Go to the source code of this file.

Functions

_GetRandomLevel

Returns a random level for the next element to be inserted. This level is geometrically distributed for p = 0.5, so perfectly suitable for an efficient Skiplist implementation.

Returns
A value between 0 and SKIPLIST_LEVELS - 1.
static __inline CHAR _GetRandomLevel ()
 
_InsertElementSkiplistWithInformation

Determines a level for the new element and inserts it at the given position in the Skiplist. This function is internally used by the Skiplist insertion functions.

Parameters
SkiplistPointer to the SKIPLIST structure to operate on.
ElementThe element to insert.
pUpdateArray containing the last nodes before our new node on each level.
dwDistanceArray containing the distance to the last node before our new node on each level.
Returns
TRUE if the node was successfully inserted, FALSE if no memory could be allocated for it.
static BOOL _InsertElementSkiplistWithInformation (PSKIPLIST Skiplist, PVOID Element, PSKIPLIST_NODE *pUpdate, DWORD *dwDistance)
 
DeleteElementSkiplist

Deletes an element from the Skiplist. The efficiency of this operation is O(log N) on average.

Instead of the result of a LookupElementSkiplist call, it's sufficient to provide a dummy element with just enough information for your CompareRoutine. A lookup for the element to be deleted needs to be performed in any case.

Parameters
SkiplistPointer to the SKIPLIST structure to operate on.
ElementInformation about the element to be deleted.
Returns
Returns the deleted element or NULL if no such element was found. You can then free memory for the deleted element if necessary.
PVOID DeleteElementSkiplist (PSKIPLIST Skiplist, PVOID Element)
 
InitializeSkiplist

Initializes a new Skiplist structure.

Parameters
SkiplistPointer to the SKIPLIST structure to operate on.
AllocateRoutinePointer to a SKIPLIST_ALLOCATE_ROUTINE for allocating memory for new Skiplist nodes.
CompareRoutinePointer to a SKIPLIST_COMPARE_ROUTINE for comparing two elements of the Skiplist.
FreeRoutinePointer to a SKIPLIST_FREE_ROUTINE for freeing memory allocated with AllocateRoutine.
void InitializeSkiplist (PSKIPLIST Skiplist, PSKIPLIST_ALLOCATE_ROUTINE AllocateRoutine, PSKIPLIST_COMPARE_ROUTINE CompareRoutine, PSKIPLIST_FREE_ROUTINE FreeRoutine)
 
InsertElementSkiplist

Inserts a new element into the Skiplist. The efficiency of this operation is O(log N) on average. Uses CompareRoutine to find the right position for the insertion.

Parameters
SkiplistPointer to the SKIPLIST structure to operate on.
ElementThe element to insert.
Returns
TRUE if the node was successfully inserted, FALSE if it already exists or no memory could be allocated for it.
BOOL InsertElementSkiplist (PSKIPLIST Skiplist, PVOID Element)
 
InsertTailElementSkiplist

Inserts a new element at the end of the Skiplist. The efficiency of this operation is O(log N) on average. In contrast to InsertElementSkiplist, this function is more efficient by not calling CompareRoutine at all and always inserting the element at the end. You're responsible for calling this function only when you can guarantee that InsertElementSkiplist would also insert the element at the end.

Parameters
SkiplistPointer to the SKIPLIST structure to operate on.
ElementThe element to insert.
Returns
TRUE if the node was successfully inserted, FALSE if it already exists or no memory could be allocated for it.
BOOL InsertTailElementSkiplist (PSKIPLIST Skiplist, PVOID Element)
 
LookupElementSkiplist

Looks up an element in the Skiplist. The efficiency of this operation is O(log N) on average.

Parameters
SkiplistPointer to the SKIPLIST structure to operate on.
ElementInformation about the element to look for.
ElementIndexPointer to a DWORD that will contain the zero-based index of the element in the Skiplist. If you're not interested in the index, you can set this parameter to NULL.
Returns
Returns the found element or NULL if no such element was found.
PVOID LookupElementSkiplist (PSKIPLIST Skiplist, PVOID Element, PDWORD ElementIndex)
 
LookupNodeByIndexSkiplist

Looks up a node in the Skiplist at the given position. The efficiency of this operation is O(log N) on average.

Parameters
SkiplistPointer to the SKIPLIST structure to operate on.
ElementIndexZero-based position of the node in the Skiplist.
Returns
Returns the found node or NULL if the position is invalid.
PSKIPLIST_NODE LookupNodeByIndexSkiplist (PSKIPLIST Skiplist, DWORD ElementIndex)
 

Function Documentation

◆ _GetRandomLevel()

static __inline CHAR _GetRandomLevel ( )
static

Definition at line 23 of file skiplist.c.

24{
25 // Using a simple fixed seed and the Park-Miller Lehmer Minimal Standard Random Number Generator gives an acceptable distribution for our "random" levels.
26 static DWORD dwRandom = 1;
27
28 DWORD dwLevel = 0;
29 DWORD dwShifted;
30
31 // Generate 31 uniformly distributed pseudo-random bits using the Park-Miller Lehmer Minimal Standard Random Number Generator.
32 dwRandom = (DWORD)(((ULONGLONG)dwRandom * 48271UL) % 2147483647UL);
33
34 // Shift out (31 - SKIPLIST_LEVELS) bits to the right to have no more than SKIPLIST_LEVELS bits set.
35 dwShifted = dwRandom >> (31 - SKIPLIST_LEVELS);
36
37 // BitScanForward doesn't operate on a zero input value.
38 if (dwShifted)
39 {
40 // BitScanForward sets dwLevel to the zero-based position of the first set bit (from LSB to MSB).
41 // This makes dwLevel a geometrically distributed value between 0 and SKIPLIST_LEVELS - 1 for p = 0.5.
42 BitScanForward(&dwLevel, dwShifted);
43 }
44
45 // dwLevel can't have a value higher than 30 this way, so a CHAR is more than enough.
46 return (CHAR)dwLevel;
47}
unsigned long DWORD
Definition: ntddk_ex.h:95
#define BitScanForward
Definition: interlocked.h:5
#define DWORD
Definition: nt_native.h:44
uint64_t ULONGLONG
Definition: typedefs.h:67
#define SKIPLIST_LEVELS
Definition: precomp.h:30
char CHAR
Definition: xmlstorage.h:175

Referenced by _InsertElementSkiplistWithInformation().

◆ _InsertElementSkiplistWithInformation()

static BOOL _InsertElementSkiplistWithInformation ( PSKIPLIST  Skiplist,
PVOID  Element,
PSKIPLIST_NODE pUpdate,
DWORD dwDistance 
)
static

Definition at line 71 of file skiplist.c.

72{
73 CHAR chNewLevel;
74 CHAR i;
75 PSKIPLIST_NODE pNode;
76
77 // Get the highest level, on which the node shall be inserted.
78 chNewLevel = _GetRandomLevel();
79
80 // Check if the new level is higher than the maximum level we currently have in the Skiplist.
81 if (chNewLevel > Skiplist->MaximumLevel)
82 {
83 // It is, so we also need to insert the new node right after the Head node on some levels.
84 // These are the levels higher than the current maximum level up to the new level.
85 // We also need to set the distance of these elements to the new node count to account for the calculations below.
86 for (i = Skiplist->MaximumLevel + 1; i <= chNewLevel; i++)
87 {
88 pUpdate[i] = &Skiplist->Head;
89 pUpdate[i]->Distance[i] = Skiplist->NodeCount + 1;
90 }
91
92 // The new level is the new maximum level of the entire Skiplist.
93 Skiplist->MaximumLevel = chNewLevel;
94 }
95
96 // Finally create our new Skiplist node.
97 pNode = Skiplist->AllocateRoutine(sizeof(SKIPLIST_NODE));
98 if (!pNode)
99 return FALSE;
100
101 pNode->Element = Element;
102
103 // For each used level, insert us between the saved node for this level and its current next node.
104 for (i = 0; i <= chNewLevel; i++)
105 {
106 pNode->Next[i] = pUpdate[i]->Next[i];
107 pUpdate[i]->Next[i] = pNode;
108
109 // We know the walked distance in this level: dwDistance[i]
110 // We also know the element index of the new node: dwDistance[0]
111 // The new node's distance is now the walked distance in this level plus the difference between the saved node's distance and the element index.
112 pNode->Distance[i] = dwDistance[i] + (pUpdate[i]->Distance[i] - dwDistance[0]);
113
114 // The saved node's distance is now the element index plus one (to account for the added node) minus the walked distance in this level.
115 pUpdate[i]->Distance[i] = dwDistance[0] + 1 - dwDistance[i];
116 }
117
118 // For all levels above the new node's level, we need to increment the distance, because we've just added our new node.
119 for (i = chNewLevel + 1; i <= Skiplist->MaximumLevel; i++)
120 ++pUpdate[i]->Distance[i];
121
122 // We've successfully added a node :)
123 ++Skiplist->NodeCount;
124 return TRUE;
125}
#define TRUE
Definition: types.h:120
#define FALSE
Definition: types.h:117
GLsizei GLenum const GLvoid GLsizei GLenum GLbyte GLbyte GLbyte GLdouble GLdouble GLdouble GLfloat GLfloat GLfloat GLint GLint GLint GLshort GLshort GLshort GLubyte GLubyte GLubyte GLuint GLuint GLuint GLushort GLushort GLushort GLbyte GLbyte GLbyte GLbyte GLdouble GLdouble GLdouble GLdouble GLfloat GLfloat GLfloat GLfloat GLint GLint GLint GLint GLshort GLshort GLshort GLshort GLubyte GLubyte GLubyte GLubyte GLuint GLuint GLuint GLuint GLushort GLushort GLushort GLushort GLboolean const GLdouble const GLfloat const GLint const GLshort const GLbyte const GLdouble const GLfloat const GLint const GLshort const GLdouble const GLfloat const GLint const GLshort const GLdouble const GLfloat const GLint const GLshort const GLdouble const GLfloat const GLint const GLshort const GLdouble const GLdouble const GLfloat const GLfloat const GLint const GLint const GLshort const GLshort const GLdouble const GLfloat const GLint const GLshort const GLdouble const GLfloat const GLint const GLshort const GLdouble const GLfloat const GLint const GLshort const GLdouble const GLfloat const GLint const GLshort const GLdouble const GLfloat const GLint const GLshort const GLdouble const GLfloat const GLint const GLshort const GLdouble const GLfloat const GLint const GLshort GLenum GLenum GLenum GLfloat GLenum GLint GLenum GLenum GLenum GLfloat GLenum GLenum GLint GLenum GLfloat GLenum GLint GLint GLushort GLenum GLenum GLfloat GLenum GLenum GLint GLfloat const GLubyte GLenum GLenum GLenum const GLfloat GLenum GLenum const GLint GLenum GLint GLint GLsizei GLsizei GLint GLenum GLenum const GLvoid GLenum GLenum const GLfloat GLenum GLenum const GLint GLenum GLenum const GLdouble GLenum GLenum const GLfloat GLenum GLenum const GLint GLsizei GLuint GLfloat GLuint GLbitfield GLfloat GLint GLuint GLboolean GLenum GLfloat GLenum GLbitfield GLenum GLfloat GLfloat GLint GLint const GLfloat GLenum GLfloat GLfloat GLint GLint GLfloat GLfloat GLint GLint const GLfloat GLint GLfloat GLfloat GLint GLfloat GLfloat GLint GLfloat GLfloat const GLdouble const GLfloat const GLdouble const GLfloat GLint i
Definition: glfuncs.h:248
static __inline CHAR _GetRandomLevel()
Definition: skiplist.c:23
DWORD Distance[SKIPLIST_LEVELS]
Definition: skiplist.h:29
struct _SKIPLIST_NODE * Next[SKIPLIST_LEVELS]
Definition: skiplist.h:30
PVOID Element
Definition: skiplist.h:31
CHAR MaximumLevel
Definition: skiplist.h:38
SKIPLIST_NODE Head
Definition: skiplist.h:37
DWORD NodeCount
Definition: skiplist.h:39
PSKIPLIST_ALLOCATE_ROUTINE AllocateRoutine
Definition: skiplist.h:40

Referenced by InsertElementSkiplist(), and InsertTailElementSkiplist().

◆ DeleteElementSkiplist()

PVOID DeleteElementSkiplist ( PSKIPLIST  Skiplist,
PVOID  Element 
)

Definition at line 146 of file skiplist.c.

147{
148 CHAR i;
149 PSKIPLIST_NODE pLastComparedNode = NULL;
150 PSKIPLIST_NODE pNode = &Skiplist->Head;
152 PVOID pReturnValue;
153
154 // Find the node on every currently used level, after which the node to be deleted must follow.
155 // This can be done efficiently by starting from the maximum level and going down a level each time a position has been found.
156 for (i = Skiplist->MaximumLevel + 1; --i >= 0;)
157 {
158 while (pNode->Next[i] && pNode->Next[i] != pLastComparedNode && Skiplist->CompareRoutine(pNode->Next[i]->Element, Element) < 0)
159 pNode = pNode->Next[i];
160
161 // Reduce the number of comparisons by not comparing the same node on different levels twice.
162 pLastComparedNode = pNode->Next[i];
163 pUpdate[i] = pNode;
164 }
165
166 // Check if the node we're looking for has been found.
167 pNode = pNode->Next[0];
168 if (!pNode || Skiplist->CompareRoutine(pNode->Element, Element) != 0)
169 {
170 // It hasn't been found, so there's nothing to delete.
171 return NULL;
172 }
173
174 // Beginning at the lowest level, remove the node from each level of the list and merge distances.
175 // We can stop as soon as we found the first level that doesn't contain the node.
176 for (i = 0; i <= Skiplist->MaximumLevel && pUpdate[i]->Next[i] == pNode; i++)
177 {
178 pUpdate[i]->Distance[i] += pNode->Distance[i] - 1;
179 pUpdate[i]->Next[i] = pNode->Next[i];
180 }
181
182 // Now decrement the distance of the corresponding node in levels higher than the deleted node's level to account for the deleted node.
183 while (i <= Skiplist->MaximumLevel)
184 {
185 --pUpdate[i]->Distance[i];
186 i++;
187 }
188
189 // Return the deleted element (so the caller can free it if necessary) and free the memory for the node itself (allocated by us).
190 pReturnValue = pNode->Element;
191 Skiplist->FreeRoutine(pNode);
192
193 // Find all levels which now contain no more nodes and reduce the maximum level of the entire Skiplist accordingly.
194 while (Skiplist->MaximumLevel > 0 && !Skiplist->Head.Next[Skiplist->MaximumLevel])
195 --Skiplist->MaximumLevel;
196
197 // We've successfully deleted the node :)
198 --Skiplist->NodeCount;
199 return pReturnValue;
200}
#define NULL
Definition: types.h:112
PSKIPLIST_COMPARE_ROUTINE CompareRoutine
Definition: skiplist.h:41
PSKIPLIST_FREE_ROUTINE FreeRoutine
Definition: skiplist.h:42

Referenced by _LocalSetJobLevel1(), _LocalSetJobLevel2(), FreeJob(), and main().

◆ InitializeSkiplist()

void InitializeSkiplist ( PSKIPLIST  Skiplist,
PSKIPLIST_ALLOCATE_ROUTINE  AllocateRoutine,
PSKIPLIST_COMPARE_ROUTINE  CompareRoutine,
PSKIPLIST_FREE_ROUTINE  FreeRoutine 
)

Definition at line 220 of file skiplist.c.

221{
222 // Store the routines.
224 Skiplist->CompareRoutine = CompareRoutine;
225 Skiplist->FreeRoutine = FreeRoutine;
226
227 // Initialize the members and pointers.
228 // The Distance array is only used when a node is non-NULL, so it doesn't need initialization.
229 Skiplist->MaximumLevel = 0;
230 Skiplist->NodeCount = 0;
231 ZeroMemory(Skiplist->Head.Next, sizeof(Skiplist->Head.Next));
232}
#define ZeroMemory
Definition: winbase.h:1712
_In_ PRTL_GENERIC_COMPARE_ROUTINE _In_ PRTL_GENERIC_ALLOCATE_ROUTINE _In_ PRTL_GENERIC_FREE_ROUTINE FreeRoutine
Definition: rtlfuncs.h:1090
_In_ PRTL_GENERIC_COMPARE_ROUTINE _In_ PRTL_GENERIC_ALLOCATE_ROUTINE AllocateRoutine
Definition: rtlfuncs.h:1089
_In_ PRTL_GENERIC_COMPARE_ROUTINE CompareRoutine
Definition: rtlfuncs.h:1088

Referenced by InitializeGlobalJobList(), InitializePrinterJobList(), InitializePrinterList(), and main().

◆ InsertElementSkiplist()

BOOL InsertElementSkiplist ( PSKIPLIST  Skiplist,
PVOID  Element 
)

Definition at line 250 of file skiplist.c.

251{
252 CHAR i;
253 DWORD dwDistance[SKIPLIST_LEVELS + 1] = { 0 };
254 PSKIPLIST_NODE pLastComparedNode = NULL;
255 PSKIPLIST_NODE pNode = &Skiplist->Head;
257
258 // Find the node on every currently used level, after which the new node needs to be inserted.
259 // This can be done efficiently by starting from the maximum level and going down a level each time a position has been found.
260 for (i = Skiplist->MaximumLevel + 1; --i >= 0;)
261 {
262 // When entering this level, we begin at the distance of the last level we walked through.
263 dwDistance[i] = dwDistance[i + 1];
264
265 while (pNode->Next[i] && pNode->Next[i] != pLastComparedNode && Skiplist->CompareRoutine(pNode->Next[i]->Element, Element) < 0)
266 {
267 // Save our position in every level when walking through the nodes.
268 dwDistance[i] += pNode->Distance[i];
269
270 // Advance to the next node.
271 pNode = pNode->Next[i];
272 }
273
274 // Reduce the number of comparisons by not comparing the same node on different levels twice.
275 pLastComparedNode = pNode->Next[i];
276 pUpdate[i] = pNode;
277 }
278
279 // Check if the node already exists in the Skiplist.
280 pNode = pNode->Next[0];
281 if (pNode && Skiplist->CompareRoutine(pNode->Element, Element) == 0)
282 {
283 // All elements to be inserted mustn't exist in the list, so we see this as a failure.
284 return FALSE;
285 }
286
287 // The rest of the procedure is the same for both insertion functions.
288 return _InsertElementSkiplistWithInformation(Skiplist, Element, pUpdate, dwDistance);
289}
static BOOL _InsertElementSkiplistWithInformation(PSKIPLIST Skiplist, PVOID Element, PSKIPLIST_NODE *pUpdate, DWORD *dwDistance)
Definition: skiplist.c:71

Referenced by _LocalSetJobLevel1(), _LocalSetJobLevel2(), CreateJob(), InitializeGlobalJobList(), InitializePrinterList(), and main().

◆ InsertTailElementSkiplist()

BOOL InsertTailElementSkiplist ( PSKIPLIST  Skiplist,
PVOID  Element 
)

Definition at line 308 of file skiplist.c.

309{
310 CHAR i;
311 DWORD dwDistance[SKIPLIST_LEVELS + 1] = { 0 };
312 PSKIPLIST_NODE pNode = &Skiplist->Head;
314
315 // Find the last node on every currently used level, after which the new node needs to be inserted.
316 // This can be done efficiently by starting from the maximum level and going down a level each time a position has been found.
317 for (i = Skiplist->MaximumLevel + 1; --i >= 0;)
318 {
319 // When entering this level, we begin at the distance of the last level we walked through.
320 dwDistance[i] = dwDistance[i + 1];
321
322 while (pNode->Next[i])
323 {
324 // Save our position in every level when walking through the nodes.
325 dwDistance[i] += pNode->Distance[i];
326
327 // Advance to the next node.
328 pNode = pNode->Next[i];
329 }
330
331 pUpdate[i] = pNode;
332 }
333
334 // The rest of the procedure is the same for both insertion functions.
335 return _InsertElementSkiplistWithInformation(Skiplist, Element, pUpdate, dwDistance);
336}

Referenced by CreateJob().

◆ LookupElementSkiplist()

PVOID LookupElementSkiplist ( PSKIPLIST  Skiplist,
PVOID  Element,
PDWORD  ElementIndex 
)

Definition at line 357 of file skiplist.c.

358{
359 CHAR i;
360 DWORD dwIndex = 0;
361 PSKIPLIST_NODE pLastComparedNode = NULL;
362 PSKIPLIST_NODE pNode = &Skiplist->Head;
363
364 // Do the efficient lookup in Skiplists:
365 // * Start from the maximum level.
366 // * Walk through all nodes on this level that come before the node we're looking for.
367 // * When we have reached such a node, go down a level and continue there.
368 // * Repeat these steps till we're in level 0, right in front of the node we're looking for.
369 for (i = Skiplist->MaximumLevel + 1; --i >= 0;)
370 {
371 while (pNode->Next[i] && pNode->Next[i] != pLastComparedNode && Skiplist->CompareRoutine(pNode->Next[i]->Element, Element) < 0)
372 {
373 dwIndex += pNode->Distance[i];
374 pNode = pNode->Next[i];
375 }
376
377 // Reduce the number of comparisons by not comparing the same node on different levels twice.
378 pLastComparedNode = pNode->Next[i];
379 }
380
381 // We must be right in front of the node we're looking for now, otherwise it doesn't exist in the Skiplist at all.
382 pNode = pNode->Next[0];
383 if (!pNode || Skiplist->CompareRoutine(pNode->Element, Element) != 0)
384 {
385 // It hasn't been found, so there's nothing to return.
386 return NULL;
387 }
388
389 // Return the index of the element if the caller is interested.
390 if (ElementIndex)
391 *ElementIndex = dwIndex;
392
393 // Return the stored element of the found node.
394 return pNode->Element;
395}

Referenced by _GetNextJobID(), _LocalGetJobLevel1(), _LocalGetJobLevel2(), _LocalOpenPrinterHandle(), LocalGetJob(), LocalScheduleJob(), LocalSetJob(), main(), and ReadJobShadowFile().

◆ LookupNodeByIndexSkiplist()

PSKIPLIST_NODE LookupNodeByIndexSkiplist ( PSKIPLIST  Skiplist,
DWORD  ElementIndex 
)

Definition at line 412 of file skiplist.c.

413{
414 CHAR i;
415 DWORD dwIndex = 0;
416 PSKIPLIST_NODE pNode = &Skiplist->Head;
417
418 // The only way the node can't be found is when the index is out of range.
419 if (ElementIndex >= Skiplist->NodeCount)
420 return NULL;
421
422 // Do the efficient lookup in Skiplists:
423 // * Start from the maximum level.
424 // * Walk through all nodes on this level that come before the node we're looking for.
425 // * When we have reached such a node, go down a level and continue there.
426 // * Repeat these steps till we're in level 0, right in front of the node we're looking for.
427 for (i = Skiplist->MaximumLevel + 1; --i >= 0;)
428 {
429 // We compare with <= instead of < here, because the added distances make up a 1-based index while ElementIndex is zero-based,
430 // so we have to jump one node further.
431 while (pNode->Next[i] && dwIndex + pNode->Distance[i] <= ElementIndex)
432 {
433 dwIndex += pNode->Distance[i];
434 pNode = pNode->Next[i];
435 }
436 }
437
438 // We are right in front of the node we're looking for now.
439 return pNode->Next[0];
440}

Referenced by LocalEnumJobs(), and main().