src/util/qsort.c File Reference
#include "util.h"
Go to the source code of this file.
Defines | |
| #define | THRESH 4 |
| #define | MTHRESH 6 |
Functions | |
| static void qst | ARGS ((char *base, char *max)) |
| void | qsort (void *vbase, size_t n, size_t size, int(*compar)(const void *, const void *)) |
| static void | qst (char *base, char *max) |
Variables | |
| static char rcsid[] | UNUSED = "$Id: qsort.c,v 1.5 2002/08/25 05:30:13 fabio Exp $" |
| static int(* | qcmp )(const void *, const void *) |
| static int | qsz |
| static int | thresh |
| static int | mthresh |
Define Documentation
Function Documentation
| static void qst ARGS | ( | (char *base, char *max) | ) | [static] |
| void qsort | ( | void * | vbase, | |
| size_t | n, | |||
| size_t | size, | |||
| int(*)(const void *, const void *) | compar | |||
| ) |
Function********************************************************************
Synopsis [Own version of the system qsort routine.]
Description [The THRESHold below is the insertion sort threshold, and has been adjusted for records of size 48 bytes. The MTHREShold is where we stop finding a better median. First, set up some global parameters for qst to share. Then, quicksort with qst(), and then a cleanup insertion sort ourselves. Sound simple? It's not...]
SideEffects []
SeeAlso [qst]
Definition at line 70 of file qsort.c.
00075 { 00076 register char c, *i, *j, *lo, *hi; 00077 char *min, *max, *base; 00078 00079 if (n <= 1) 00080 return; 00081 base = (char *) vbase; 00082 qsz = size; 00083 qcmp = compar; 00084 thresh = qsz * THRESH; 00085 mthresh = qsz * MTHRESH; 00086 max = base + n * qsz; 00087 if (n >= THRESH) { 00088 qst(base, max); 00089 hi = base + thresh; 00090 } else { 00091 hi = max; 00092 } 00093 /* 00094 * First put smallest element, which must be in the first THRESH, in 00095 * the first position as a sentinel. This is done just by searching 00096 * the first THRESH elements (or the first n if n < THRESH), finding 00097 * the min, and swapping it into the first position. 00098 */ 00099 for (j = lo = base; (lo += qsz) < hi; ) 00100 if ((*qcmp)(j, lo) > 0) 00101 j = lo; 00102 if (j != base) { 00103 /* swap j into place */ 00104 for (i = base, hi = base + qsz; i < hi; ) { 00105 c = *j; 00106 *j++ = *i; 00107 *i++ = c; 00108 } 00109 } 00110 /* 00111 * With our sentinel in place, we now run the following hyper-fast 00112 * insertion sort. For each remaining element, min, from [1] to [n-1], 00113 * set hi to the index of the element AFTER which this one goes. 00114 * Then, do the standard insertion sort shift on a character at a time 00115 * basis for each element in the frob. 00116 */ 00117 for (min = base; (hi = min += qsz) < max; ) { 00118 while ((*qcmp)(hi -= qsz, min) > 0) 00119 /* void */; 00120 if ((hi += qsz) != min) { 00121 for (lo = min + qsz; --lo >= min; ) { 00122 c = *lo; 00123 for (i = j = lo; (j -= qsz) >= hi; i = j) 00124 *i = *j; 00125 *i = c; 00126 } 00127 } 00128 } 00129 }
| static void qst | ( | char * | base, | |
| char * | max | |||
| ) | [static] |
Function********************************************************************
Synopsis [Effectively perform qsort]
Description [First, find the median element, and put that one in the first place as the discriminator. (This "median" is just the median of the first, last and middle elements). (Using this median instead of the first element is a big win). Then, the usual partitioning/swapping, followed by moving the discriminator into the right place. Then, figure out the sizes of the two partions, do the smaller one recursively and the larger one via a repeat of this code. Stopping when there are less than THRESH elements in a partition and cleaning up with an insertion sort (in our caller) is a huge win. All data swaps are done in-line, which is space-losing but time-saving. (And there are only three places where this is done).]
SideEffects []
SeeAlso [qsort]
Definition at line 156 of file qsort.c.
00157 { 00158 register char c, *i, *j, *jj; 00159 register int ii; 00160 char *mid, *tmp; 00161 int lo, hi; 00162 00163 /* 00164 * At the top here, lo is the number of characters of elements in the 00165 * current partition. (Which should be max - base). 00166 * Find the median of the first, last, and middle element and make 00167 * that the middle element. Set j to largest of first and middle. 00168 * If max is larger than that guy, then it's that guy, else compare 00169 * max with loser of first and take larger. Things are set up to 00170 * prefer the middle, then the first in case of ties. 00171 */ 00172 lo = max - base; /* number of elements as chars */ 00173 do { 00174 mid = i = base + qsz * ((lo / qsz) >> 1); 00175 if (lo >= mthresh) { 00176 j = ((*qcmp)((jj = base), i) > 0 ? jj : i); 00177 if ((*qcmp)(j, (tmp = max - qsz)) > 0) { 00178 /* switch to first loser */ 00179 j = (j == jj ? i : jj); 00180 if ((*qcmp)(j, tmp) < 0) 00181 j = tmp; 00182 } 00183 if (j != i) { 00184 ii = qsz; 00185 do { 00186 c = *i; 00187 *i++ = *j; 00188 *j++ = c; 00189 } while (--ii); 00190 } 00191 } 00192 /* 00193 * Semi-standard quicksort partitioning/swapping 00194 */ 00195 for (i = base, j = max - qsz; ; ) { 00196 while (i < mid && (*qcmp)(i, mid) <= 0) 00197 i += qsz; 00198 while (j > mid) { 00199 if ((*qcmp)(mid, j) <= 0) { 00200 j -= qsz; 00201 continue; 00202 } 00203 tmp = i + qsz; /* value of i after swap */ 00204 if (i == mid) { 00205 /* j <-> mid, new mid is j */ 00206 mid = jj = j; 00207 } else { 00208 /* i <-> j */ 00209 jj = j; 00210 j -= qsz; 00211 } 00212 goto swap; 00213 } 00214 if (i == mid) { 00215 break; 00216 } else { 00217 /* i <-> mid, new mid is i */ 00218 jj = mid; 00219 tmp = mid = i; /* value of i after swap */ 00220 j -= qsz; 00221 } 00222 swap: 00223 ii = qsz; 00224 do { 00225 c = *i; 00226 *i++ = *jj; 00227 *jj++ = c; 00228 } while (--ii); 00229 i = tmp; 00230 } 00231 /* 00232 * Look at sizes of the two partitions, do the smaller 00233 * one first by recursion, then do the larger one by 00234 * making sure lo is its size, base and max are update 00235 * correctly, and branching back. But only repeat 00236 * (recursively or by branching) if the partition is 00237 * of at least size THRESH. 00238 */ 00239 i = (j = mid) + qsz; 00240 if ((lo = j - base) <= (hi = max - i)) { 00241 if (lo >= thresh) 00242 qst(base, j); 00243 base = i; 00244 lo = hi; 00245 } else { 00246 if (hi >= thresh) 00247 qst(i, max); 00248 max = j; 00249 } 00250 } while (lo >= thresh); 00251 }
Variable Documentation
int(* qcmp)(const void *, const void *) [static] |
char rcsid [] UNUSED = "$Id: qsort.c,v 1.5 2002/08/25 05:30:13 fabio Exp $" [static] |
CFile***********************************************************************
FileName [qsort.c]
PackageName [util]
Synopsis [Our own qsort routine.]
Author []
Copyright [Copyright (c) 1994-1996 The Regents of the Univ. of California. All rights reserved.
Permission is hereby granted, without written agreement and without license or royalty fees, to use, copy, modify, and distribute this software and its documentation for any purpose, provided that the above copyright notice and the following two paragraphs appear in all copies of this software.
IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.]
