Redis-pqsort

1.pqsort原理分析

2.源码

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#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) { \
//i means es包含多少个TYPE \
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); \
}
/*
swaptype:
0: es == sizeof(long)
1: a或者es为sizeof(long)整数倍,但是es != sizeof(long)
2: a和es都不是sizeof(long)的整数倍
*/
#define SWAPINIT(a, es) swaptype = ((char *)a - (char *)0) % sizeof(long) || \
es % sizeof(long) ? 2 : es == sizeof(long)? 0 : 1;
//n = es, ie交换的a和b指向的元素的内存大小
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)
}
//交换a和b指向的内存
#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) //swaptype =1或者2
#define vecswap(a, b, n) if ((n) > 0) swapfunc((a), (b), (size_t)(n), swaptype)
//找到a, b, c的中间值
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;
//init swaptype
loop: SWAPINIT(a, es);
if (n < 7) {
//采用插入排序
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;
//快排
for (;;) {
//pa左边的都是等于a[0]的元素
while (pb <= pc && (cmp_result = cmp(pb, a)) <= 0) {
if (cmp_result == 0) {
swap(pa, pb);
pa += es;
}
pb += es;
}
//pd右边的都是等于a[0]的元素
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;
//pb-pa=小于a[0]的Bytes
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);
//left
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);
}
//right
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);*/
}
/*
sort a[lrange, rrange]
es: ElementSize
a: array
n: 数组元素个数
cmp: CallBack Func
*/
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);
}