commit 0de81911525bc62bc2a8fc52a368102afed7022b
parent 853311e5b1c1d9fe9d006e3a4f322e9916764933
Author: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Mon, 28 Oct 2024 14:14:54 -0300
New structure to count keys in a table for rehashing
Diffstat:
| M | ltable.c | | | 115 | +++++++++++++++++++++++++++++++++++++++++++++---------------------------------- |
1 file changed, 65 insertions(+), 50 deletions(-)
diff --git a/ltable.c b/ltable.c
@@ -456,15 +456,29 @@ static int keyinarray (Table *t, lua_Integer key) {
** ==============================================================
*/
+
/*
-** Compute the optimal size for the array part of table 't'. 'nums' is a
-** "count array" where 'nums[i]' is the number of integers in the table
-** between 2^(i - 1) + 1 and 2^i. 'pna' enters with the total number of
-** integer keys in the table and leaves with the number of keys that
-** will go to the array part; return the optimal size. (The condition
-** 'twotoi > 0' in the for loop stops the loop if 'twotoi' overflows.)
+** Structure to count the keys in a table.
+** 'total' is the total number of keys in the table.
+** 'na' is the number of *array indices* in the table (see 'arrayindex').
+** 'nums' is a "count array" where 'nums[i]' is the number of integer
+** keys between 2^(i - 1) + 1 and 2^i. Note that 'na' is the summation
+** of 'nums'.
*/
-static unsigned computesizes (unsigned nums[], unsigned *pna) {
+typedef struct {
+ unsigned total;
+ unsigned na;
+ unsigned nums[MAXABITS + 1];
+} Counters;
+
+/*
+** Compute the optimal size for the array part of table 't'.
+** 'ct->na' enters with the total number of array indices in the table
+** and leaves with the number of keys that will go to the array part;
+** return the optimal size. (The condition 'twotoi > 0' in the for loop
+** stops the loop if 'twotoi' overflows.)
+*/
+static unsigned computesizes (Counters *ct) {
int i;
unsigned int twotoi; /* 2^i (candidate for optimal size) */
unsigned int a = 0; /* number of elements smaller than 2^i */
@@ -472,28 +486,26 @@ static unsigned computesizes (unsigned nums[], unsigned *pna) {
unsigned int optimal = 0; /* optimal size for array part */
/* loop while keys can fill more than half of total size */
for (i = 0, twotoi = 1;
- twotoi > 0 && *pna > twotoi / 2;
+ twotoi > 0 && ct->na > twotoi / 2;
i++, twotoi *= 2) {
- a += nums[i];
+ a += ct->nums[i];
if (a > twotoi/2) { /* more than half elements present? */
optimal = twotoi; /* optimal size (till now) */
na = a; /* all elements up to 'optimal' will go to array part */
}
}
lua_assert((optimal == 0 || optimal / 2 < na) && na <= optimal);
- *pna = na;
+ ct->na = na;
return optimal;
}
-static unsigned countint (lua_Integer key, unsigned int *nums) {
+static void countint (lua_Integer key, Counters *ct) {
unsigned int k = arrayindex(key);
- if (k != 0) { /* is 'key' an appropriate array index? */
- nums[luaO_ceillog2(k)]++; /* count as such */
- return 1;
+ if (k != 0) { /* is 'key' an array index? */
+ ct->nums[luaO_ceillog2(k)]++; /* count as such */
+ ct->na++;
}
- else
- return 0;
}
@@ -504,11 +516,9 @@ l_sinline int arraykeyisempty (const Table *t, lua_Unsigned key) {
/*
-** Count keys in array part of table 't': Fill 'nums[i]' with
-** number of keys that will go into corresponding slice and return
-** total number of non-nil keys.
+** Count keys in array part of table 't'.
*/
-static unsigned numusearray (const Table *t, unsigned *nums) {
+static void numusearray (const Table *t, Counters *ct) {
int lg;
unsigned int ttlg; /* 2^lg */
unsigned int ause = 0; /* summation of 'nums' */
@@ -528,27 +538,29 @@ static unsigned numusearray (const Table *t, unsigned *nums) {
if (!arraykeyisempty(t, i))
lc++;
}
- nums[lg] += lc;
+ ct->nums[lg] += lc;
ause += lc;
}
- return ause;
+ ct->total += ause;
+ ct->na += ause;
}
-static unsigned numusehash (const Table *t, unsigned *nums, unsigned *pna) {
- unsigned totaluse = 0; /* total number of elements */
- unsigned ause = 0; /* elements added to 'nums' (can go to array part) */
+/*
+** Count keys in hash part of table 't'.
+*/
+static void numusehash (const Table *t, Counters *ct) {
unsigned i = sizenode(t);
+ unsigned total = 0;
while (i--) {
Node *n = &t->node[i];
if (!isempty(gval(n))) {
+ total++;
if (keyisinteger(n))
- ause += countint(keyival(n), nums);
- totaluse++;
+ countint(keyival(n), ct);
}
}
- *pna += ause;
- return totaluse;
+ ct->total += total;
}
@@ -566,12 +578,11 @@ static size_t concretesize (unsigned int size) {
** do nothing. Else, if new size is zero, free the old array. (It must
** be present, as the sizes are different.) Otherwise, allocate a new
** array, move the common elements to new proper position, and then
-** frees old array.
-** When array grows, we could reallocate it, but we still would need
-** to move the elements to their new position, so the copy implicit
-** in realloc is a waste. When array shrinks, it always erases some
-** elements that should still be in the array, so we must reallocate in
-** two steps anyway. It is simpler to always reallocate in two steps.
+** frees the old array.
+** We could reallocate the array, but we still would need to move the
+** elements to their new position, so the copy implicit in realloc is a
+** waste. Moreover, most allocators will move the array anyway when the
+** new size is double the old one (the most common case).
*/
static Value *resizearray (lua_State *L , Table *t,
unsigned oldasize,
@@ -590,10 +601,10 @@ static Value *resizearray (lua_State *L , Table *t,
if (np == NULL) /* allocation error? */
return NULL;
if (oldasize > 0) {
+ /* move common elements to new position */
Value *op = t->array - oldasize; /* real original array */
unsigned tomove = (oldasize < newasize) ? oldasize : newasize;
lua_assert(tomove > 0);
- /* move common elements to new position */
memcpy(np + newasize - tomove,
op + oldasize - tomove,
concretesize(tomove));
@@ -723,6 +734,9 @@ static void clearNewSlice (Table *t, unsigned oldasize, unsigned newasize) {
** into the table, initializes the new part of the array (if any) with
** nils and reinserts the elements of the old hash back into the new
** parts of the table.
+** Note that if the new size for the arry part ('newasize') is equal to
+** the old one ('oldasize'), this function will do nothing with that
+** part.
*/
void luaH_resize (lua_State *L, Table *t, unsigned newasize,
unsigned nhsize) {
@@ -762,33 +776,34 @@ void luaH_resizearray (lua_State *L, Table *t, unsigned int nasize) {
luaH_resize(L, t, nasize, nsize);
}
+
/*
-** nums[i] = number of keys 'k' where 2^(i - 1) < k <= 2^i
+** Rehash a table. First, count its keys. If there are array indices
+** outside the array part, compute the new best size for that part.
+** Then, resize the table.
*/
static void rehash (lua_State *L, Table *t, const TValue *ek) {
unsigned asize; /* optimal size for array part */
- unsigned na = 0; /* number of keys candidate for the array part */
- unsigned nums[MAXABITS + 1];
+ Counters ct;
unsigned i;
- unsigned totaluse; /* total number of keys */
- for (i = 0; i <= MAXABITS; i++) nums[i] = 0; /* reset counts */
setlimittosize(t);
- totaluse = 1; /* count extra key */
+ /* reset counts */
+ for (i = 0; i <= MAXABITS; i++) ct.nums[i] = 0;
+ ct.na = 0;
+ ct.total = 1; /* count extra key */
if (ttisinteger(ek))
- na += countint(ivalue(ek), nums); /* extra key may go to array */
- totaluse += numusehash(t, nums, &na); /* count keys in hash part */
- if (na == 0) {
+ countint(ivalue(ek), &ct); /* extra key may go to array */
+ numusehash(t, &ct); /* count keys in hash part */
+ if (ct.na == 0) {
/* no new keys to enter array part; keep it with the same size */
asize = luaH_realasize(t);
}
else { /* compute best size for array part */
- unsigned n = numusearray(t, nums); /* count keys in array part */
- totaluse += n; /* all keys in array part are keys */
- na += n; /* all keys in array part are candidates for new array part */
- asize = computesizes(nums, &na); /* compute new size for array part */
+ numusearray(t, &ct); /* count keys in array part */
+ asize = computesizes(&ct); /* compute new size for array part */
}
/* resize the table to new computed sizes */
- luaH_resize(L, t, asize, totaluse - na);
+ luaH_resize(L, t, asize, ct.total - ct.na);
}
