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randomness in pivot for 'table.sort' done by a macro (easier to change)

This commit is contained in:
Roberto Ierusalimschy 2015-11-20 10:30:20 -02:00
parent d103312661
commit 146508b28e
1 changed files with 17 additions and 11 deletions
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28
ltablib.c
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@ -1,5 +1,5 @@
/* /*
** $Id: ltablib.c,v 1.84 2015/11/06 16:07:14 roberto Exp roberto $ ** $Id: ltablib.c,v 1.85 2015/11/12 18:07:25 roberto Exp roberto $
** Library for Table Manipulation ** Library for Table Manipulation
** See Copyright Notice in lua.h ** See Copyright Notice in lua.h
*/ */
@ -12,7 +12,6 @@
#include <limits.h> #include <limits.h>
#include <stddef.h> #include <stddef.h>
#include <time.h>
#include "lua.h" #include "lua.h"
@ -24,10 +23,10 @@
** Operations that an object must define to mimic a table ** Operations that an object must define to mimic a table
** (some functions only need some of them) ** (some functions only need some of them)
*/ */
#define TAB_R 1 #define TAB_R 1 /* read */
#define TAB_W 2 #define TAB_W 2 /* write */
#define TAB_L 4 #define TAB_L 4 /* length */
#define TAB_RW (TAB_R | TAB_W) #define TAB_RW (TAB_R | TAB_W) /* read/write */
#define aux_getn(L,n,w) (checktab(L, n, (w) | TAB_L), luaL_len(L, n)) #define aux_getn(L,n,w) (checktab(L, n, (w) | TAB_L), luaL_len(L, n))
@ -51,7 +50,7 @@ static void checktab (lua_State *L, int arg, int what) {
(!(what & TAB_W) || checkfield(L, "__newindex", ++n)) && (!(what & TAB_W) || checkfield(L, "__newindex", ++n)) &&
(!(what & TAB_L) || checkfield(L, "__len", ++n))) { (!(what & TAB_L) || checkfield(L, "__len", ++n))) {
lua_pop(L, n); /* pop metatable and tested metamethods */ lua_pop(L, n); /* pop metatable and tested metamethods */
} }
else else
luaL_argerror(L, arg, "table expected"); /* force an error */ luaL_argerror(L, arg, "table expected"); /* force an error */
} }
@ -295,8 +294,12 @@ static int partition (lua_State *L, int lo, int up) {
/* /*
** Choose a "random" pivot in the middle part of the interval [lo, up]. ** Choose a "random" pivot in the middle part of the interval [lo, up].
** Use 'time' and 'clock' as sources of "randomness". ** (If you don't want/need this "randomness", (lo+up)/2 is an excelent
** choice.)
*/ */
#if !defined(l_sortpivot)
/* Use 'time' and 'clock' as sources of "randomness" */
#include <time.h>
static int choosePivot (int lo, int up) { static int choosePivot (int lo, int up) {
unsigned int t = (unsigned int)(unsigned long)time(NULL); /* time */ unsigned int t = (unsigned int)(unsigned long)time(NULL); /* time */
unsigned int c = (unsigned int)(unsigned long)clock(); /* clock */ unsigned int c = (unsigned int)(unsigned long)clock(); /* clock */
@ -306,11 +309,14 @@ static int choosePivot (int lo, int up) {
return (int)p; return (int)p;
} }
#define l_sortpivot(lo,up) choosePivot(lo,up)
#endif
static void auxsort (lua_State *L, int lo, int up) { static void auxsort (lua_State *L, int lo, int up) {
while (lo < up) { /* loop for tail recursion */ while (lo < up) { /* loop for tail recursion */
int p; int p; /* Pivot index */
/* sort elements 'lo', '(lo + up)/2' and 'up' */ /* sort elements 'lo', 'p', and 'up' */
lua_geti(L, 1, lo); lua_geti(L, 1, lo);
lua_geti(L, 1, up); lua_geti(L, 1, up);
if (sort_comp(L, -1, -2)) /* a[up] < a[lo]? */ if (sort_comp(L, -1, -2)) /* a[up] < a[lo]? */
@ -322,7 +328,7 @@ static void auxsort (lua_State *L, int lo, int up) {
if (up - lo < 100) /* small interval? */ if (up - lo < 100) /* small interval? */
p = (lo + up)/2; /* middle element is a good pivot */ p = (lo + up)/2; /* middle element is a good pivot */
else /* for larger intervals, it is worth a random pivot */ else /* for larger intervals, it is worth a random pivot */
p = choosePivot(lo, up); p = l_sortpivot(lo, up);
lua_geti(L, 1, p); lua_geti(L, 1, p);
lua_geti(L, 1, lo); lua_geti(L, 1, lo);
if (sort_comp(L, -2, -1)) /* a[p] < a[lo]? */ if (sort_comp(L, -2, -1)) /* a[p] < a[lo]? */