redis qsort源码阅读

      /* The following is the NetBSD libc qsort implementation modified in order to
       * support partial sorting of ranges for Redis.
       *
       * Copyright(C) 2009-2012 Salvatore Sanfilippo. All rights reserved.
       *
       * The original copyright notice follows. */
      /* $NetBSD: qsort.c,v 1.19 2009/01/30 23:38:44 lukem Exp $ */
      /*-
       * Copyright (c) 1992, 1993
       * The Regents of the University of California. All rights reserved.
       *
       * Redistribution and use in source and binary forms, with or without
       * modification, are permitted provided that the following conditions
       * are met:
       * 1. Redistributions of source code must retain the above copyright
       * notice, this list of conditions and the following disclaimer.
       * 2. Redistributions in binary form must reproduce the above copyright
       * notice, this list of conditions and the following disclaimer in the
       * documentation and/or other materials provided with the distribution.
       * 3. Neither the name of the University nor the names of its contributors
       * may be used to endorse or promote products derived from this software
       * without specific prior written permission.
       *
       * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
       * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
       * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
       * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
       * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
       * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
       * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
       * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
       * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
       * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
       * SUCH DAMAGE.
       */
      #include <sys/types.h>
      #include <errno.h>
      #include <stdlib.h>
      static inline char *med3 (char *, char *, char *,
      int (*)(const void *, const void *));
      static inline void swapfunc (char *, char *, size_t, int);
      #define min(a, b) (a) < (b) ? a : b
      /*
       * Qsort routine from Bentley & McIlroy's "Engineering a Sort Function".
       */
      #define swapcode(TYPE, parmi, parmj, n) { \
     
       size_t i = (n) / sizeof (TYPE); \
       TYPE *pi = (TYPE *)(void *)(parmi); \
       TYPE *pj = (TYPE *)(void *)(parmj); \
       do { \
       TYPE t = *pi; \
       *pi++ = *pj; \
       *pj++ = t; \
       } while (--i > 0); \
      }
      #define SWAPINIT(a, es) swaptype = ((char *)a - (char *)0) % sizeof(long) || \
     
       es % sizeof(long) ? 2 : es == sizeof(long)? 0 : 1;
      static inline void
      swapfunc(char *a, char *b, size_t n, int swaptype)
      {
     	if (swaptype <= 1)
      		swapcode(long, a, b, n)
     	else
      		swapcode(char, a, b, n)
      }
      #define swap(a, b) \
     
     	if (swaptype == 0) { \
     		long t = *(long *)(void *)(a);			\
      		*(long *)(void *)(a) = *(long *)(void *)(b);	\
      		*(long *)(void *)(b) = t;			\
      	} else \
      		swapfunc(a, b, es, swaptype)
      #define vecswap(a, b, n) if ((n) > 0) swapfunc((a), (b), (size_t)(n), swaptype)
      static inline char *
      med3(char *a, char *b, char *c,
      int (*cmp) (const void *, const void *))
      {
     	return cmp(a, b) < 0 ?
       (cmp(b, c) < 0 ? b : (cmp(a, c) < 0 ? c : a ))
       :(cmp(b, c) > 0 ? b : (cmp(a, c) < 0 ? a : c ));
      }
      static void
      _pqsort(void *a, size_t n, size_t es,
      int (*cmp) (const void *, const void *), void *lrange, void *rrange)
      {
     	char *pa, *pb, *pc, *pd, *pl, *pm, *pn;
     	size_t d, r;
     	int swaptype, cmp_result;
      loop:	SWAPINIT(a, es);
     	if (n < 7) {
     		for (pm = (char *) a + es; pm < (char *) a + n * es; pm += es)
     			for (pl = pm; pl > (char *) a && cmp(pl - es, pl) > 0;
       pl -= es)
       swap(pl, pl - es);
     		return;
      	}
      	pm = (char *) a + (n / 2) * es;
     	if (n > 7) {
      		pl = (char *) a;
      		pn = (char *) a + (n - 1) * es;
     		if (n > 40) {
      			d = (n / 8) * es;
      			pl = med3(pl, pl + d, pl + 2 * d, cmp);
      			pm = med3(pm - d, pm, pm + d, cmp);
      			pn = med3(pn - 2 * d, pn - d, pn, cmp);
      		}
      		pm = med3(pl, pm, pn, cmp);
      	}
      	swap(a, pm);
      	pa = pb = (char *) a + es;
      	pc = pd = (char *) a + (n - 1) * es;
     	for (;;) {
     		while (pb <= pc && (cmp_result = cmp(pb, a)) <= 0) {
     			if (cmp_result == 0) {
       swap(pa, pb);
       pa += es;
      			}
      			pb += es;
      		}
     		while (pb <= pc && (cmp_result = cmp(pc, a)) >= 0) {
     			if (cmp_result == 0) {
       swap(pc, pd);
       pd -= es;
      			}
      			pc -= es;
      		}
     		if (pb > pc)
     			break;
      		swap(pb, pc);
      		pb += es;
      		pc -= es;
      	}
      	pn = (char *) a + n * es;
      	r = min(pa - (char *) a, pb - pa);
      	vecswap(a, pb - r, r);
      	r = min((size_t)(pd - pc), pn - pd - es);
      	vecswap(pb, pn - r, r);
     	if ((r = pb - pa) > es) {
      void *_l = a, *_r = ((unsigned char*)a)+r-1;
      if (!((lrange < _l && rrange < _l) ||
       (lrange > _r && rrange > _r)))
       _pqsort(a, r / es, es, cmp, lrange, rrange);
       }
     	if ((r = pd - pc) > es) {
      void *_l, *_r;
     		/* Iterate rather than recurse to save stack space */
      		a = pn - r;
      		n = r / es;
       _l = a;
       _r = ((unsigned char*)a)+r-1;
      if (!((lrange < _l && rrange < _l) ||
       (lrange > _r && rrange > _r)))
      goto loop;
      	}
      /* qsort(pn - r, r / es, es, cmp);*/
      }
      void
      pqsort(void *a, size_t n, size_t es,
      int (*cmp) (const void *, const void *), size_t lrange, size_t rrange)
      {
       _pqsort(a,n,es,cmp,((unsigned char*)a)+(lrange*es),
       ((unsigned char*)a)+((rrange+1)*es)-1);
      }
  
 

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