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usr/src/common/util/qsort.c

author | Saso Kiselkov <skiselkov@gmail.com> |

Fri, 12 Apr 2013 17:49:42 -0400 | |

changeset 14014 | 626936c65627 |

parent 6812 | febeba71273d |

permissions | -rw-r--r-- |

3708 Fast reboot support in ixgbe
Reviewed by: Garrett D'Amore <[email protected]>
Reviewed by: Richard Lowe <[email protected]>
Approved by: Dan McDonald <[email protected]>

/* * CDDL HEADER START * * The contents of this file are subject to the terms of the * Common Development and Distribution License (the "License"). * You may not use this file except in compliance with the License. * * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE * or http://www.opensolaris.org/os/licensing. * See the License for the specific language governing permissions * and limitations under the License. * * When distributing Covered Code, include this CDDL HEADER in each * file and include the License file at usr/src/OPENSOLARIS.LICENSE. * If applicable, add the following below this CDDL HEADER, with the * fields enclosed by brackets "[]" replaced with your own identifying * information: Portions Copyright [yyyy] [name of copyright owner] * * CDDL HEADER END */ /* * Copyright 2008 Sun Microsystems, Inc. All rights reserved. * Use is subject to license terms. */ #pragma ident "%Z%%M% %I% %E% SMI" #if !defined(_KERNEL) && !defined(_KMDB) #include "lint.h" #endif /* !_KERNEL && !_KMDB */ #include <sys/types.h> #if !defined(_KERNEL) && !defined(_KMDB) #include <stdlib.h> #include <synch.h> #endif /* !_KERNEL && !_KMDB */ #include "qsort.h" static void swapp32(uint32_t *r1, uint32_t *r2, size_t cnt); static void swapp64(uint64_t *r1, uint64_t *r2, size_t cnt); static void swapi(uint32_t *r1, uint32_t *r2, size_t cnt); static void swapb(char *r1, char *r2, size_t cnt); /* * choose a median of 3 values * * note: cstyle specifically prohibits nested conditional operators * but this is the only way to do the median of 3 function in-line */ #define med3(a, b, c) (cmp((a), (b)) < 0) \ ? ((cmp((b), (c)) < 0) ? (b) : (cmp((a), (c)) < 0) ? (c) : (a)) \ : ((cmp((b), (c)) > 0) ? (b) : (cmp((a), (c)) > 0) ? (c) : (a)) #define THRESH_L 5 /* threshold for insertion sort */ #define THRESH_M3 20 /* threshold for median of 3 */ #define THRESH_M9 50 /* threshold for median of 9 */ typedef struct { char *b_lim; size_t nrec; } stk_t; /* * qsort() is a general purpose, in-place sorting routine using a * user provided call back function for comparisons. This implementation * utilizes a ternary quicksort algorithm, and cuts over to an * insertion sort for partitions involving fewer than THRESH_L records. * * Potential User Errors * There is no return value from qsort, this function has no method * of alerting the user that a sort did not work or could not work. * We do not print an error message or exit the process or thread, * Even if we can detect an error, We CANNOT silently return without * sorting the data, if we did so the user could never be sure the * sort completed successfully. * It is possible we could change the return value of sort from void * to int and return success or some error codes, but this gets into * standards and compatibility issues. * * Examples of qsort parameter errors might be * 1) record size (rsiz) equal to 0 * qsort will loop and never return. * 2) record size (rsiz) less than 0 * rsiz is unsigned, so a negative value is insanely large * 3) number of records (nrec) is 0 * This is legal - qsort will return without examining any records * 4) number of records (nrec) is less than 0 * nrec is unsigned, so a negative value is insanely large. * 5) nrec * rsiz > memory allocation for sort array * a segment violation may occur * corruption of other memory may occur * 6) The base address of the sort array is invalid * a segment violation may occur * corruption of other memory may occur * 7) The user call back function is invalid * we may get alignment errors or segment violations * we may jump into never-never land * * Some less obvious errors might be * 8) The user compare function is not comparing correctly * 9) The user compare function modifies the data records */ void qsort( void *basep, size_t nrec, size_t rsiz, int (*cmp)(const void *, const void *)) { size_t i; /* temporary variable */ /* variables used by swap */ void (*swapf)(char *, char *, size_t); size_t loops; /* variables used by sort */ stk_t stack[8 * sizeof (nrec) + 1]; stk_t *sp; char *b_lim; /* bottom limit */ char *b_dup; /* bottom duplicate */ char *b_par; /* bottom partition */ char *t_lim; /* top limit */ char *t_dup; /* top duplicate */ char *t_par; /* top partition */ char *m1, *m2, *m3; /* median pointers */ uintptr_t d_bytelength; /* byte length of duplicate records */ int b_nrec; int t_nrec; int cv; /* results of compare (bottom / top) */ /* * choose a swap function based on alignment and size * * The qsort function sorts an array of fixed length records. * We have very limited knowledge about the data record itself. * It may be that the data record is in the array we are sorting * or it may be that the array contains pointers or indexes to * the actual data record and all that we are sorting is the indexes. * * The following decision will choose an optimal swap function * based on the size and alignment of the data records * swapp64 will swap 64 bit pointers * swapp32 will swap 32 bit pointers * swapi will swap an array of 32 bit integers * swapb will swap an array of 8 bit characters * * swapi and swapb will also require the variable loops to be set * to control the length of the array being swapped */ if ((((uintptr_t)basep & (sizeof (uint64_t) - 1)) == 0) && (rsiz == sizeof (uint64_t))) { loops = 1; swapf = (void (*)(char *, char *, size_t))swapp64; } else if ((((uintptr_t)basep & (sizeof (uint32_t) - 1)) == 0) && (rsiz == sizeof (uint32_t))) { loops = 1; swapf = (void (*)(char *, char *, size_t))swapp32; } else if ((((uintptr_t)basep & (sizeof (uint32_t) - 1)) == 0) && ((rsiz & (sizeof (uint32_t) - 1)) == 0)) { loops = rsiz / sizeof (int); swapf = (void (*)(char *, char *, size_t))swapi; } else { loops = rsiz; swapf = swapb; } /* * qsort is a partitioning sort * * the stack is the bookkeeping mechanism to keep track of all * the partitions. * * each sort pass takes one partition and sorts it into two partitions. * at the top of the loop we simply take the partition on the top * of the stack and sort it. See the comments at the bottom * of the loop regarding which partitions to add in what order. * * initially put the whole partition on the stack */ sp = stack; sp->b_lim = (char *)basep; sp->nrec = nrec; sp++; while (sp > stack) { sp--; b_lim = sp->b_lim; nrec = sp->nrec; /* * a linear insertion sort i faster than a qsort for * very small number of records (THRESH_L) * * if number records < threshold use linear insertion sort * * this also handles the special case where the partition * 0 or 1 records length. */ if (nrec < THRESH_L) { /* * Linear insertion sort */ t_par = b_lim; for (i = 1; i < nrec; i++) { t_par += rsiz; b_par = t_par; while (b_par > b_lim) { b_par -= rsiz; if ((*cmp)(b_par, b_par + rsiz) <= 0) { break; } (*swapf)(b_par, b_par + rsiz, loops); } } /* * a linear insertion sort will put all records * in their final position and will not create * subpartitions. * * therefore when the insertion sort is complete * just go to the top of the loop and get the * next partition to sort. */ continue; } /* quicksort */ /* * choose a pivot record * * Ideally the pivot record will divide the partition * into two equal parts. however we have to balance the * work involved in selecting the pivot record with the * expected benefit. * * The choice of pivot record depends on the number of * records in the partition * * for small partitions (nrec < THRESH_M3) * we just select the record in the middle of the partition * * if (nrec >= THRESH_M3 && nrec < THRESH_M9) * we select three values and choose the median of 3 * * if (nrec >= THRESH_M9) * then we use an approximate median of 9 * 9 records are selected and grouped in 3 groups of 3 * the median of each of these 3 groups is fed into another * median of 3 decision. * * Each median of 3 decision is 2 or 3 compares, * so median of 9 costs between 8 and 12 compares. * * i is byte distance between two consecutive samples * m2 will point to the pivot record */ if (nrec < THRESH_M3) { m2 = b_lim + (nrec / 2) * rsiz; } else if (nrec < THRESH_M9) { /* use median of 3 */ i = ((nrec - 1) / 2) * rsiz; m2 = med3(b_lim, b_lim + i, b_lim + 2 * i); } else { /* approx median of 9 */ i = ((nrec - 1) / 8) * rsiz; m1 = med3(b_lim, b_lim + i, b_lim + 2 * i); m2 = med3(b_lim + 3 * i, b_lim + 4 * i, b_lim + 5 * i); m3 = med3(b_lim + 6 * i, b_lim + 7 * i, b_lim + 8 * i); m2 = med3(m1, m2, m3); } /* * quick sort partitioning * * The partition limits are defined by bottom and top pointers * b_lim and t_lim. * * qsort uses a fairly standard method of moving the * partitioning pointers, b_par and t_par, to the middle of * the partition and exchanging records that are in the * wrong part of the partition. * * Two enhancements have been made to the basic algorithm. * One for handling duplicate records and one to minimize * the number of swaps. * * Two duplicate records pointers are (b_dup and t_dup) are * initially set to b_lim and t_lim. Each time a record * whose sort key value is equal to the pivot record is found * it will be swapped with the record pointed to by * b_dup or t_dup and the duplicate pointer will be * incremented toward the center. * When partitioning is complete, all the duplicate records * will have been collected at the upper and lower limits of * the partition and can easily be moved adjacent to the * pivot record. * * The second optimization is to minimize the number of swaps. * The pointer m2 points to the pivot record. * During partitioning, if m2 is ever equal to the partitioning * pointers, b_par or t_par, then b_par or t_par just moves * onto the next record without doing a compare. * If as a result of duplicate record detection, * b_dup or t_dup is ever equal to m2, * then m2 is changed to point to the duplicate record and * b_dup or t_dup is incremented with out swapping records. * * When partitioning is done, we may not have the same pivot * record that we started with, but we will have one with * an equal sort key. */ b_dup = b_par = b_lim; t_dup = t_par = t_lim = b_lim + rsiz * (nrec - 1); for (;;) { /* move bottom pointer up */ for (; b_par <= t_par; b_par += rsiz) { if (b_par == m2) { continue; } cv = cmp(b_par, m2); if (cv > 0) { break; } if (cv == 0) { if (b_dup == m2) { m2 = b_par; } else if (b_dup != b_par) { (*swapf)(b_dup, b_par, loops); } b_dup += rsiz; } } /* move top pointer down */ for (; b_par < t_par; t_par -= rsiz) { if (t_par == m2) { continue; } cv = cmp(t_par, m2); if (cv < 0) { break; } if (cv == 0) { if (t_dup == m2) { m2 = t_par; } else if (t_dup != t_par) { (*swapf)(t_dup, t_par, loops); } t_dup -= rsiz; } } /* break if we are done partitioning */ if (b_par >= t_par) { break; } /* exchange records at upper and lower break points */ (*swapf)(b_par, t_par, loops); b_par += rsiz; t_par -= rsiz; } /* * partitioning is now complete * * there are two termination conditions from the partitioning * loop above. Either b_par or t_par have crossed or * they are equal. * * we need to swap the pivot record to its final position * m2 could be in either the upper or lower partitions * or it could already be in its final position */ /* * R[b_par] > R[m2] * R[t_par] < R[m2] */ if (t_par < b_par) { if (m2 < t_par) { (*swapf)(m2, t_par, loops); m2 = b_par = t_par; } else if (m2 > b_par) { (*swapf)(m2, b_par, loops); m2 = t_par = b_par; } else { b_par = t_par = m2; } } else { if (m2 < t_par) { t_par = b_par = t_par - rsiz; } if (m2 != b_par) { (*swapf)(m2, b_par, loops); } m2 = t_par; } /* * move bottom duplicates next to pivot * optimized to eliminate overlap */ d_bytelength = b_dup - b_lim; if (b_par - b_dup < d_bytelength) { b_dup = b_lim + (b_par - b_dup); } while (b_dup > b_lim) { b_dup -= rsiz; b_par -= rsiz; (*swapf)(b_dup, b_par, loops); } b_par = m2 - d_bytelength; /* * move top duplicates next to pivot */ d_bytelength = t_lim - t_dup; if (t_dup - t_par < d_bytelength) { t_dup = t_lim - (t_dup - t_par); } while (t_dup < t_lim) { t_dup += rsiz; t_par += rsiz; (*swapf)(t_dup, t_par, loops); } t_par = m2 + d_bytelength; /* * when a qsort pass completes there are three partitions * 1) the lower contains all records less than pivot * 2) the upper contains all records greater than pivot * 3) the pivot partition contains all record equal to pivot * * all records in the pivot partition are in their final * position and do not need to be accounted for by the stack * * when adding partitions to the stack * it is important to add the largest partition first * to prevent stack overflow. * * calculate number of unsorted records in top and bottom * push resulting partitions on stack */ b_nrec = (b_par - b_lim) / rsiz; t_nrec = (t_lim - t_par) / rsiz; if (b_nrec < t_nrec) { sp->b_lim = t_par + rsiz; sp->nrec = t_nrec; sp++; sp->b_lim = b_lim; sp->nrec = b_nrec; sp++; } else { sp->b_lim = b_lim; sp->nrec = b_nrec; sp++; sp->b_lim = t_par + rsiz; sp->nrec = t_nrec; sp++; } } } /* * The following swap functions should not create a stack frame * the SPARC call / return instruction will be executed * but the a save / restore will not be executed * which means we won't do a window turn with the spill / fill overhead * verify this by examining the assembly code */ /* ARGSUSED */ static void swapp32(uint32_t *r1, uint32_t *r2, size_t cnt) { uint32_t temp; temp = *r1; *r1++ = *r2; *r2++ = temp; } /* ARGSUSED */ static void swapp64(uint64_t *r1, uint64_t *r2, size_t cnt) { uint64_t temp; temp = *r1; *r1++ = *r2; *r2++ = temp; } static void swapi(uint32_t *r1, uint32_t *r2, size_t cnt) { uint32_t temp; /* character by character */ while (cnt--) { temp = *r1; *r1++ = *r2; *r2++ = temp; } } static void swapb(char *r1, char *r2, size_t cnt) { char temp; /* character by character */ while (cnt--) { temp = *r1; *r1++ = *r2; *r2++ = temp; } }