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[unleashed/tickless.git] / usr / src / common / util / qsort.c
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1 /*
2 * CDDL HEADER START
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
19 * CDDL HEADER END
23 * Copyright 2008 Sun Microsystems, Inc. All rights reserved.
24 * Use is subject to license terms.
27 #pragma ident "%Z%%M% %I% %E% SMI"
29 #if !defined(_KERNEL) && !defined(_KMDB)
30 #include "lint.h"
31 #endif /* !_KERNEL && !_KMDB */
33 #include <sys/types.h>
35 #if !defined(_KERNEL) && !defined(_KMDB)
36 #include <stdlib.h>
37 #include <synch.h>
38 #endif /* !_KERNEL && !_KMDB */
40 #include "qsort.h"
42 static void swapp32(uint32_t *r1, uint32_t *r2, size_t cnt);
43 static void swapp64(uint64_t *r1, uint64_t *r2, size_t cnt);
44 static void swapi(uint32_t *r1, uint32_t *r2, size_t cnt);
45 static void swapb(char *r1, char *r2, size_t cnt);
48 * choose a median of 3 values
50 * note: cstyle specifically prohibits nested conditional operators
51 * but this is the only way to do the median of 3 function in-line
53 #define med3(a, b, c) (cmp((a), (b)) < 0) \
54 ? ((cmp((b), (c)) < 0) ? (b) : (cmp((a), (c)) < 0) ? (c) : (a)) \
55 : ((cmp((b), (c)) > 0) ? (b) : (cmp((a), (c)) > 0) ? (c) : (a))
57 #define THRESH_L 5 /* threshold for insertion sort */
58 #define THRESH_M3 20 /* threshold for median of 3 */
59 #define THRESH_M9 50 /* threshold for median of 9 */
61 typedef struct {
62 char *b_lim;
63 size_t nrec;
64 } stk_t;
67 * qsort() is a general purpose, in-place sorting routine using a
68 * user provided call back function for comparisons. This implementation
69 * utilizes a ternary quicksort algorithm, and cuts over to an
70 * insertion sort for partitions involving fewer than THRESH_L records.
72 * Potential User Errors
73 * There is no return value from qsort, this function has no method
74 * of alerting the user that a sort did not work or could not work.
75 * We do not print an error message or exit the process or thread,
76 * Even if we can detect an error, We CANNOT silently return without
77 * sorting the data, if we did so the user could never be sure the
78 * sort completed successfully.
79 * It is possible we could change the return value of sort from void
80 * to int and return success or some error codes, but this gets into
81 * standards and compatibility issues.
83 * Examples of qsort parameter errors might be
84 * 1) record size (rsiz) equal to 0
85 * qsort will loop and never return.
86 * 2) record size (rsiz) less than 0
87 * rsiz is unsigned, so a negative value is insanely large
88 * 3) number of records (nrec) is 0
89 * This is legal - qsort will return without examining any records
90 * 4) number of records (nrec) is less than 0
91 * nrec is unsigned, so a negative value is insanely large.
92 * 5) nrec * rsiz > memory allocation for sort array
93 * a segment violation may occur
94 * corruption of other memory may occur
95 * 6) The base address of the sort array is invalid
96 * a segment violation may occur
97 * corruption of other memory may occur
98 * 7) The user call back function is invalid
99 * we may get alignment errors or segment violations
100 * we may jump into never-never land
102 * Some less obvious errors might be
103 * 8) The user compare function is not comparing correctly
104 * 9) The user compare function modifies the data records
107 void
108 qsort(
109 void *basep,
110 size_t nrec,
111 size_t rsiz,
112 int (*cmp)(const void *, const void *))
114 size_t i; /* temporary variable */
116 /* variables used by swap */
117 void (*swapf)(char *, char *, size_t);
118 size_t loops;
120 /* variables used by sort */
121 stk_t stack[8 * sizeof (nrec) + 1];
122 stk_t *sp;
123 char *b_lim; /* bottom limit */
124 char *b_dup; /* bottom duplicate */
125 char *b_par; /* bottom partition */
126 char *t_lim; /* top limit */
127 char *t_dup; /* top duplicate */
128 char *t_par; /* top partition */
129 char *m1, *m2, *m3; /* median pointers */
130 uintptr_t d_bytelength; /* byte length of duplicate records */
131 int b_nrec;
132 int t_nrec;
133 int cv; /* results of compare (bottom / top) */
136 * choose a swap function based on alignment and size
138 * The qsort function sorts an array of fixed length records.
139 * We have very limited knowledge about the data record itself.
140 * It may be that the data record is in the array we are sorting
141 * or it may be that the array contains pointers or indexes to
142 * the actual data record and all that we are sorting is the indexes.
144 * The following decision will choose an optimal swap function
145 * based on the size and alignment of the data records
146 * swapp64 will swap 64 bit pointers
147 * swapp32 will swap 32 bit pointers
148 * swapi will swap an array of 32 bit integers
149 * swapb will swap an array of 8 bit characters
151 * swapi and swapb will also require the variable loops to be set
152 * to control the length of the array being swapped
154 if ((((uintptr_t)basep & (sizeof (uint64_t) - 1)) == 0) &&
155 (rsiz == sizeof (uint64_t))) {
156 loops = 1;
157 swapf = (void (*)(char *, char *, size_t))swapp64;
158 } else if ((((uintptr_t)basep & (sizeof (uint32_t) - 1)) == 0) &&
159 (rsiz == sizeof (uint32_t))) {
160 loops = 1;
161 swapf = (void (*)(char *, char *, size_t))swapp32;
162 } else if ((((uintptr_t)basep & (sizeof (uint32_t) - 1)) == 0) &&
163 ((rsiz & (sizeof (uint32_t) - 1)) == 0)) {
164 loops = rsiz / sizeof (int);
165 swapf = (void (*)(char *, char *, size_t))swapi;
166 } else {
167 loops = rsiz;
168 swapf = swapb;
172 * qsort is a partitioning sort
174 * the stack is the bookkeeping mechanism to keep track of all
175 * the partitions.
177 * each sort pass takes one partition and sorts it into two partitions.
178 * at the top of the loop we simply take the partition on the top
179 * of the stack and sort it. See the comments at the bottom
180 * of the loop regarding which partitions to add in what order.
182 * initially put the whole partition on the stack
184 sp = stack;
185 sp->b_lim = (char *)basep;
186 sp->nrec = nrec;
187 sp++;
188 while (sp > stack) {
189 sp--;
190 b_lim = sp->b_lim;
191 nrec = sp->nrec;
194 * a linear insertion sort i faster than a qsort for
195 * very small number of records (THRESH_L)
197 * if number records < threshold use linear insertion sort
199 * this also handles the special case where the partition
200 * 0 or 1 records length.
202 if (nrec < THRESH_L) {
204 * Linear insertion sort
206 t_par = b_lim;
207 for (i = 1; i < nrec; i++) {
208 t_par += rsiz;
209 b_par = t_par;
210 while (b_par > b_lim) {
211 b_par -= rsiz;
212 if ((*cmp)(b_par, b_par + rsiz) <= 0) {
213 break;
215 (*swapf)(b_par, b_par + rsiz, loops);
220 * a linear insertion sort will put all records
221 * in their final position and will not create
222 * subpartitions.
224 * therefore when the insertion sort is complete
225 * just go to the top of the loop and get the
226 * next partition to sort.
228 continue;
231 /* quicksort */
234 * choose a pivot record
236 * Ideally the pivot record will divide the partition
237 * into two equal parts. however we have to balance the
238 * work involved in selecting the pivot record with the
239 * expected benefit.
241 * The choice of pivot record depends on the number of
242 * records in the partition
244 * for small partitions (nrec < THRESH_M3)
245 * we just select the record in the middle of the partition
247 * if (nrec >= THRESH_M3 && nrec < THRESH_M9)
248 * we select three values and choose the median of 3
250 * if (nrec >= THRESH_M9)
251 * then we use an approximate median of 9
252 * 9 records are selected and grouped in 3 groups of 3
253 * the median of each of these 3 groups is fed into another
254 * median of 3 decision.
256 * Each median of 3 decision is 2 or 3 compares,
257 * so median of 9 costs between 8 and 12 compares.
259 * i is byte distance between two consecutive samples
260 * m2 will point to the pivot record
262 if (nrec < THRESH_M3) {
263 m2 = b_lim + (nrec / 2) * rsiz;
264 } else if (nrec < THRESH_M9) {
265 /* use median of 3 */
266 i = ((nrec - 1) / 2) * rsiz;
267 m2 = med3(b_lim, b_lim + i, b_lim + 2 * i);
268 } else {
269 /* approx median of 9 */
270 i = ((nrec - 1) / 8) * rsiz;
271 m1 = med3(b_lim, b_lim + i, b_lim + 2 * i);
272 m2 = med3(b_lim + 3 * i, b_lim + 4 * i, b_lim + 5 * i);
273 m3 = med3(b_lim + 6 * i, b_lim + 7 * i, b_lim + 8 * i);
274 m2 = med3(m1, m2, m3);
278 * quick sort partitioning
280 * The partition limits are defined by bottom and top pointers
281 * b_lim and t_lim.
283 * qsort uses a fairly standard method of moving the
284 * partitioning pointers, b_par and t_par, to the middle of
285 * the partition and exchanging records that are in the
286 * wrong part of the partition.
288 * Two enhancements have been made to the basic algorithm.
289 * One for handling duplicate records and one to minimize
290 * the number of swaps.
292 * Two duplicate records pointers are (b_dup and t_dup) are
293 * initially set to b_lim and t_lim. Each time a record
294 * whose sort key value is equal to the pivot record is found
295 * it will be swapped with the record pointed to by
296 * b_dup or t_dup and the duplicate pointer will be
297 * incremented toward the center.
298 * When partitioning is complete, all the duplicate records
299 * will have been collected at the upper and lower limits of
300 * the partition and can easily be moved adjacent to the
301 * pivot record.
303 * The second optimization is to minimize the number of swaps.
304 * The pointer m2 points to the pivot record.
305 * During partitioning, if m2 is ever equal to the partitioning
306 * pointers, b_par or t_par, then b_par or t_par just moves
307 * onto the next record without doing a compare.
308 * If as a result of duplicate record detection,
309 * b_dup or t_dup is ever equal to m2,
310 * then m2 is changed to point to the duplicate record and
311 * b_dup or t_dup is incremented with out swapping records.
313 * When partitioning is done, we may not have the same pivot
314 * record that we started with, but we will have one with
315 * an equal sort key.
317 b_dup = b_par = b_lim;
318 t_dup = t_par = t_lim = b_lim + rsiz * (nrec - 1);
319 for (;;) {
321 /* move bottom pointer up */
322 for (; b_par <= t_par; b_par += rsiz) {
323 if (b_par == m2) {
324 continue;
326 cv = cmp(b_par, m2);
327 if (cv > 0) {
328 break;
330 if (cv == 0) {
331 if (b_dup == m2) {
332 m2 = b_par;
333 } else if (b_dup != b_par) {
334 (*swapf)(b_dup, b_par, loops);
336 b_dup += rsiz;
340 /* move top pointer down */
341 for (; b_par < t_par; t_par -= rsiz) {
342 if (t_par == m2) {
343 continue;
345 cv = cmp(t_par, m2);
346 if (cv < 0) {
347 break;
349 if (cv == 0) {
350 if (t_dup == m2) {
351 m2 = t_par;
352 } else if (t_dup != t_par) {
353 (*swapf)(t_dup, t_par, loops);
355 t_dup -= rsiz;
359 /* break if we are done partitioning */
360 if (b_par >= t_par) {
361 break;
364 /* exchange records at upper and lower break points */
365 (*swapf)(b_par, t_par, loops);
366 b_par += rsiz;
367 t_par -= rsiz;
371 * partitioning is now complete
373 * there are two termination conditions from the partitioning
374 * loop above. Either b_par or t_par have crossed or
375 * they are equal.
377 * we need to swap the pivot record to its final position
378 * m2 could be in either the upper or lower partitions
379 * or it could already be in its final position
382 * R[b_par] > R[m2]
383 * R[t_par] < R[m2]
385 if (t_par < b_par) {
386 if (m2 < t_par) {
387 (*swapf)(m2, t_par, loops);
388 m2 = b_par = t_par;
389 } else if (m2 > b_par) {
390 (*swapf)(m2, b_par, loops);
391 m2 = t_par = b_par;
392 } else {
393 b_par = t_par = m2;
395 } else {
396 if (m2 < t_par) {
397 t_par = b_par = t_par - rsiz;
399 if (m2 != b_par) {
400 (*swapf)(m2, b_par, loops);
402 m2 = t_par;
406 * move bottom duplicates next to pivot
407 * optimized to eliminate overlap
409 d_bytelength = b_dup - b_lim;
410 if (b_par - b_dup < d_bytelength) {
411 b_dup = b_lim + (b_par - b_dup);
413 while (b_dup > b_lim) {
414 b_dup -= rsiz;
415 b_par -= rsiz;
416 (*swapf)(b_dup, b_par, loops);
418 b_par = m2 - d_bytelength;
421 * move top duplicates next to pivot
423 d_bytelength = t_lim - t_dup;
424 if (t_dup - t_par < d_bytelength) {
425 t_dup = t_lim - (t_dup - t_par);
427 while (t_dup < t_lim) {
428 t_dup += rsiz;
429 t_par += rsiz;
430 (*swapf)(t_dup, t_par, loops);
432 t_par = m2 + d_bytelength;
435 * when a qsort pass completes there are three partitions
436 * 1) the lower contains all records less than pivot
437 * 2) the upper contains all records greater than pivot
438 * 3) the pivot partition contains all record equal to pivot
440 * all records in the pivot partition are in their final
441 * position and do not need to be accounted for by the stack
443 * when adding partitions to the stack
444 * it is important to add the largest partition first
445 * to prevent stack overflow.
447 * calculate number of unsorted records in top and bottom
448 * push resulting partitions on stack
450 b_nrec = (b_par - b_lim) / rsiz;
451 t_nrec = (t_lim - t_par) / rsiz;
452 if (b_nrec < t_nrec) {
453 sp->b_lim = t_par + rsiz;
454 sp->nrec = t_nrec;
455 sp++;
456 sp->b_lim = b_lim;
457 sp->nrec = b_nrec;
458 sp++;
459 } else {
460 sp->b_lim = b_lim;
461 sp->nrec = b_nrec;
462 sp++;
463 sp->b_lim = t_par + rsiz;
464 sp->nrec = t_nrec;
465 sp++;
471 * The following swap functions should not create a stack frame
472 * the SPARC call / return instruction will be executed
473 * but the a save / restore will not be executed
474 * which means we won't do a window turn with the spill / fill overhead
475 * verify this by examining the assembly code
478 /* ARGSUSED */
479 static void
480 swapp32(uint32_t *r1, uint32_t *r2, size_t cnt)
482 uint32_t temp;
484 temp = *r1;
485 *r1++ = *r2;
486 *r2++ = temp;
489 /* ARGSUSED */
490 static void
491 swapp64(uint64_t *r1, uint64_t *r2, size_t cnt)
493 uint64_t temp;
495 temp = *r1;
496 *r1++ = *r2;
497 *r2++ = temp;
500 static void
501 swapi(uint32_t *r1, uint32_t *r2, size_t cnt)
503 uint32_t temp;
505 /* character by character */
506 while (cnt--) {
507 temp = *r1;
508 *r1++ = *r2;
509 *r2++ = temp;
513 static void
514 swapb(char *r1, char *r2, size_t cnt)
516 char temp;
518 /* character by character */
519 while (cnt--) {
520 temp = *r1;
521 *r1++ = *r2;
522 *r2++ = temp;