/**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.] ******************************************************************************/ #include "util.h" #ifndef lint static char rcsid[] UNUSED = "$Id: qsort.c,v 1.5 2002/08/25 05:30:13 fabio Exp $"; #endif #define THRESH 4 /* threshold for insertion */ #define MTHRESH 6 /* threshold for median */ static int (*qcmp)(const void *, const void *); /* the comparison routine */ static int qsz; /* size of each record */ static int thresh; /* THRESHold in chars */ static int mthresh; /* MTHRESHold in chars */ static void qst ARGS((char *base, char *max)); /*---------------------------------------------------------------------------*/ /* Definition of exported functions */ /*---------------------------------------------------------------------------*/ #undef min #undef max /**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] ******************************************************************************/ void qsort( void *vbase, size_t n, size_t size, int (*compar)(const void *, const void *)) { register char c, *i, *j, *lo, *hi; char *min, *max, *base; if (n <= 1) return; base = (char *) vbase; qsz = size; qcmp = compar; thresh = qsz * THRESH; mthresh = qsz * MTHRESH; max = base + n * qsz; if (n >= THRESH) { qst(base, max); hi = base + thresh; } else { hi = max; } /* * First put smallest element, which must be in the first THRESH, in * the first position as a sentinel. This is done just by searching * the first THRESH elements (or the first n if n < THRESH), finding * the min, and swapping it into the first position. */ for (j = lo = base; (lo += qsz) < hi; ) if ((*qcmp)(j, lo) > 0) j = lo; if (j != base) { /* swap j into place */ for (i = base, hi = base + qsz; i < hi; ) { c = *j; *j++ = *i; *i++ = c; } } /* * With our sentinel in place, we now run the following hyper-fast * insertion sort. For each remaining element, min, from [1] to [n-1], * set hi to the index of the element AFTER which this one goes. * Then, do the standard insertion sort shift on a character at a time * basis for each element in the frob. */ for (min = base; (hi = min += qsz) < max; ) { while ((*qcmp)(hi -= qsz, min) > 0) /* void */; if ((hi += qsz) != min) { for (lo = min + qsz; --lo >= min; ) { c = *lo; for (i = j = lo; (j -= qsz) >= hi; i = j) *i = *j; *i = c; } } } } /*---------------------------------------------------------------------------*/ /* Definition of static functions */ /*---------------------------------------------------------------------------*/ /**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] ******************************************************************************/ static void qst(char *base, char *max) { register char c, *i, *j, *jj; register int ii; char *mid, *tmp; int lo, hi; /* * At the top here, lo is the number of characters of elements in the * current partition. (Which should be max - base). * Find the median of the first, last, and middle element and make * that the middle element. Set j to largest of first and middle. * If max is larger than that guy, then it's that guy, else compare * max with loser of first and take larger. Things are set up to * prefer the middle, then the first in case of ties. */ lo = max - base; /* number of elements as chars */ do { mid = i = base + qsz * ((lo / qsz) >> 1); if (lo >= mthresh) { j = ((*qcmp)((jj = base), i) > 0 ? jj : i); if ((*qcmp)(j, (tmp = max - qsz)) > 0) { /* switch to first loser */ j = (j == jj ? i : jj); if ((*qcmp)(j, tmp) < 0) j = tmp; } if (j != i) { ii = qsz; do { c = *i; *i++ = *j; *j++ = c; } while (--ii); } } /* * Semi-standard quicksort partitioning/swapping */ for (i = base, j = max - qsz; ; ) { while (i < mid && (*qcmp)(i, mid) <= 0) i += qsz; while (j > mid) { if ((*qcmp)(mid, j) <= 0) { j -= qsz; continue; } tmp = i + qsz; /* value of i after swap */ if (i == mid) { /* j <-> mid, new mid is j */ mid = jj = j; } else { /* i <-> j */ jj = j; j -= qsz; } goto swap; } if (i == mid) { break; } else { /* i <-> mid, new mid is i */ jj = mid; tmp = mid = i; /* value of i after swap */ j -= qsz; } swap: ii = qsz; do { c = *i; *i++ = *jj; *jj++ = c; } while (--ii); i = tmp; } /* * Look at sizes of the two partitions, do the smaller * one first by recursion, then do the larger one by * making sure lo is its size, base and max are update * correctly, and branching back. But only repeat * (recursively or by branching) if the partition is * of at least size THRESH. */ i = (j = mid) + qsz; if ((lo = j - base) <= (hi = max - i)) { if (lo >= thresh) qst(base, j); base = i; lo = hi; } else { if (hi >= thresh) qst(i, max); max = j; } } while (lo >= thresh); }