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change in hash algorithm so that it does not need empty slot

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(tables can be 100% full)
This commit is contained in:
Roberto Ierusalimschy
2005-01-05 16:20:51 -02:00
parent 65726f3e2e
commit e2498e079e
9 changed files with 125 additions and 108 deletions
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191
ltable.c
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@@ -1,5 +1,5 @@
/*
** $Id: ltable.c,v 2.12 2004/12/04 18:10:22 roberto Exp $
** $Id: ltable.c,v 2.13 2005/01/04 15:55:12 roberto Exp roberto $
** Lua tables (hash)
** See Copyright Notice in lua.h
*/
@@ -68,6 +68,13 @@
#define numints cast(int, sizeof(lua_Number)/sizeof(int))
const Node luaH_dummynode = {
{{NULL}, LUA_TNIL}, /* value */
{{NULL}, LUA_TNIL, NULL} /* key */
};
/*
** hash for lua_Numbers
*/
@@ -176,31 +183,32 @@ int luaH_next (lua_State *L, Table *t, StkId key) {
*/
static void computesizes (int nums[], int ntotal, int *narray, int *nhash) {
static int computesizes (int nums[], int *narray) {
int i;
int a = nums[0]; /* number of elements smaller than 2^i */
int na = a; /* number of elements to go to array part */
int n = (na == 0) ? -1 : 0; /* (log of) optimal size for array part */
for (i = 1; a < *narray && *narray >= twoto(i-1); i++) {
int twotoi; /* 2^i */
int a = 0; /* number of elements smaller than 2^i */
int na = 0; /* number of elements to go to array part */
int n = 0; /* optimal size for array part */
for (i = 0, twotoi = 1; twotoi/2 < *narray; i++, twotoi *= 2) {
if (nums[i] > 0) {
a += nums[i];
if (a >= twoto(i-1)) { /* more than half elements in use? */
n = i;
na = a;
if (a > twotoi/2) { /* more than half elements present? */
n = twotoi; /* optimal size (till now) */
na = a; /* all elements smaller than n will go to array part */
}
}
if (a == *narray) break; /* all elements already counted */
}
lua_assert(na <= *narray && *narray <= ntotal);
*nhash = ntotal - na;
*narray = (n == -1) ? 0 : twoto(n);
lua_assert(na <= *narray && na >= *narray/2);
*narray = n;
lua_assert(*narray/2 <= na && na <= *narray);
return na;
}
static int countint (const TValue *key, int *nums) {
int k = arrayindex(key);
if (0 < k && k <= MAXASIZE) { /* is `key' an appropriate array index? */
nums[luaO_log2(k-1)+1]++; /* count as such */
nums[ceillog2(k)]++; /* count as such */
return 1;
}
else
@@ -208,40 +216,44 @@ static int countint (const TValue *key, int *nums) {
}
static void numuse (const Table *t, int *narray, int *nhash, const TValue *ek) {
int nums[MAXBITS+1];
int i, lg;
int totaluse = 0;
/* count elements in array part */
for (i=0, lg=0; lg<=MAXBITS; lg++) { /* for each slice [2^(lg-1) to 2^lg) */
int ttlg = twoto(lg); /* 2^lg */
if (ttlg > t->sizearray) {
ttlg = t->sizearray;
if (i >= ttlg) break;
static int numusearray (const Table *t, int *nums) {
int lg;
int ttlg; /* 2^lg */
int ause = 0; /* summation of `nums' */
int i = 1; /* count to traverse all array keys */
for (lg=0, ttlg=1; lg<=MAXBITS; lg++, ttlg*=2) { /* for each slice */
int lc = 0; /* counter */
int lim = ttlg;
if (lim > t->sizearray) {
lim = t->sizearray; /* adjust upper limit */
if (i > lim)
break; /* no more elements to count */
}
nums[lg] = 0;
for (; i<ttlg; i++) {
if (!ttisnil(&t->array[i])) {
nums[lg]++;
totaluse++;
}
/* count elements in range (2^(lg-1), 2^lg] */
for (; i <= lim; i++) {
if (!ttisnil(&t->array[i-1]))
lc++;
}
nums[lg] += lc;
ause += lc;
}
for (; lg<=MAXBITS; lg++) nums[lg] = 0; /* reset other counts */
*narray = totaluse; /* all previous uses were in array part */
/* count elements in hash part */
i = sizenode(t);
return ause;
}
static int numusehash (const Table *t, int *nums, int *pnasize) {
int totaluse = 0; /* total number of elements */
int ause = 0; /* summation of `nums' */
int i = sizenode(t);
while (i--) {
Node *n = &t->node[i];
if (!ttisnil(gval(n))) {
*narray += countint(key2tval(n), nums);
ause += countint(key2tval(n), nums);
totaluse++;
}
}
/* count extra key */
*narray += countint(ek, nums);
totaluse++;
computesizes(nums, totaluse, narray, nhash);
*pnasize += ause;
return totaluse;
}
@@ -254,18 +266,18 @@ static void setarrayvector (lua_State *L, Table *t, int size) {
}
static void setnodevector (lua_State *L, Table *t, int lsize) {
int i;
int size = twoto(lsize);
if (lsize > MAXBITS)
luaG_runerror(L, "table overflow");
if (lsize == 0) { /* no elements to hash part? */
t->node = G(L)->dummynode; /* use common `dummynode' */
lua_assert(ttisnil(gkey(t->node))); /* assert invariants: */
lua_assert(ttisnil(gval(t->node)));
lua_assert(gnext(t->node) == NULL); /* (`dummynode' must be empty) */
static void setnodevector (lua_State *L, Table *t, int size) {
int lsize;
if (size == 0) { /* no elements to hash part? */
t->node = cast(Node *, &luaH_dummynode); /* use common `dummynode' */
lsize = 0;
}
else {
int i;
lsize = ceillog2(size);
if (lsize > MAXBITS)
luaG_runerror(L, "table overflow");
size = twoto(lsize);
t->node = luaM_newvector(L, size, Node);
for (i=0; i<size; i++) {
gnext(&t->node[i]) = NULL;
@@ -274,31 +286,19 @@ static void setnodevector (lua_State *L, Table *t, int lsize) {
}
}
t->lsizenode = cast(lu_byte, lsize);
t->firstfree = gnode(t, size-1); /* first free position to be used */
t->lastfree = gnode(t, size); /* all positions are free */
}
static void luaH_resize (lua_State *L, Table *t, int nasize, int nhsize) {
static void resize (lua_State *L, Table *t, int nasize, int nhsize) {
int i;
int oldasize = t->sizearray;
int oldhsize = t->lsizenode;
Node *nold;
Node temp[1];
if (oldhsize)
nold = t->node; /* save old hash ... */
else { /* old hash is `dummynode' */
lua_assert(t->node == G(L)->dummynode);
temp[0] = t->node[0]; /* copy it to `temp' */
nold = temp;
setnilvalue(gkey(G(L)->dummynode)); /* restate invariant */
setnilvalue(gval(G(L)->dummynode));
lua_assert(gnext(G(L)->dummynode) == NULL);
}
Node *nold = t->node; /* save old hash ... */
if (nasize > oldasize) /* array part must grow? */
setarrayvector(L, t, nasize);
/* create new hash part with appropriate size */
setnodevector(L, t, nhsize);
/* re-insert elements */
if (nasize < oldasize) { /* array part must shrink? */
t->sizearray = nasize;
/* re-insert elements from vanishing slice */
@@ -309,28 +309,39 @@ static void luaH_resize (lua_State *L, Table *t, int nasize, int nhsize) {
/* shrink array */
luaM_reallocvector(L, t->array, oldasize, nasize, TValue);
}
/* re-insert elements in hash part */
/* re-insert elements from hash part */
for (i = twoto(oldhsize) - 1; i >= 0; i--) {
Node *old = nold+i;
if (!ttisnil(gval(old)))
setobjt2t(L, luaH_set(L, t, key2tval(old)), gval(old));
}
if (oldhsize)
if (nold != &luaH_dummynode)
luaM_freearray(L, nold, twoto(oldhsize), Node); /* free old array */
}
void luaH_resizearray (lua_State *L, Table *t, int nasize) {
luaH_resize(L, t, nasize, t->lsizenode);
int nsize = (t->node == &luaH_dummynode) ? 0 : sizenode(t);
resize(L, t, nasize, nsize);
}
static void rehash (lua_State *L, Table *t, const TValue *ek) {
int nasize, nhsize;
/* compute new sizes for array and hash parts */
numuse(t, &nasize, &nhsize, ek);
int nasize, na;
int nums[MAXBITS+1]; /* nums[i] = number of keys between 2^(i-1) and 2^i */
int i;
int totaluse;
for (i=0; i<=MAXBITS; i++) nums[i] = 0; /* reset counts */
nasize = numusearray(t, nums); /* count keys in array part */
totaluse = nasize; /* all those keys are integer keys */
totaluse += numusehash(t, nums, &nasize); /* count keys in hash part */
/* count extra key */
nasize += countint(ek, nums);
totaluse++;
/* compute new size for array part */
na = computesizes(nums, &nasize);
/* resize the table to new computed sizes */
luaH_resize(L, t, nasize, luaO_log2(nhsize)+1);
resize(L, t, nasize, totaluse - na);
}
@@ -349,21 +360,30 @@ Table *luaH_new (lua_State *L, int narray, int nhash) {
t->array = NULL;
t->sizearray = 0;
t->lsizenode = 0;
t->node = NULL;
t->node = cast(Node *, &luaH_dummynode);
setarrayvector(L, t, narray);
setnodevector(L, t, luaO_log2(nhash)+1);
setnodevector(L, t, nhash);
return t;
}
void luaH_free (lua_State *L, Table *t) {
if (t->lsizenode)
if (t->node != &luaH_dummynode)
luaM_freearray(L, t->node, sizenode(t), Node);
luaM_freearray(L, t->array, t->sizearray, TValue);
luaM_free(L, t);
}
static Node *getfreepos (lua_State *L, Table *t) {
while (t->lastfree-- > t->node) {
if (ttisnil(gkey(t->lastfree)))
return t->lastfree;
}
return NULL; /* could not find a free place */
}
/*
** inserts a new key into a hash table; first, check whether key's main
@@ -374,10 +394,15 @@ void luaH_free (lua_State *L, Table *t) {
*/
static TValue *newkey (lua_State *L, Table *t, const TValue *key) {
Node *mp = luaH_mainposition(t, key);
if (!ttisnil(gval(mp))) { /* main position is not free? */
/* `mp' of colliding node */
Node *othern = luaH_mainposition(t, key2tval(mp));
Node *n = t->firstfree; /* get a free place */
if (!ttisnil(gval(mp)) || mp == &luaH_dummynode) {
Node *othern;
Node *n = getfreepos(L, t); /* get a free place */
if (n == NULL) { /* cannot find a free place? */
rehash(L, t, key); /* grow table */
return luaH_set(L, t, key); /* re-insert key into grown table */
}
lua_assert(n != &luaH_dummynode);
othern = luaH_mainposition(t, key2tval(mp));
if (othern != mp) { /* is colliding node out of its main position? */
/* yes; move colliding node into free position */
while (gnext(othern) != mp) othern = gnext(othern); /* find previous */
@@ -396,15 +421,7 @@ static TValue *newkey (lua_State *L, Table *t, const TValue *key) {
gkey(mp)->value = key->value; gkey(mp)->tt = key->tt;
luaC_barriert(L, t, key);
lua_assert(ttisnil(gval(mp)));
for (;;) { /* correct `firstfree' */
if (ttisnil(gkey(t->firstfree)))
return gval(mp); /* OK; table still has a free place */
else if (t->firstfree == t->node) break; /* cannot decrement from here */
else (t->firstfree)--;
}
/* no more free places; must create one */
rehash(L, t, key); /* grow table */
return luaH_set(L, t, key); /* re-insert in new table */
return gval(mp);
}