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Full abstraction for representation of array values

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This commit is contained in:
Roberto Ierusalimschy
2023-10-30 14:25:59 -03:00
parent b8b709b6d4
commit 43c8e5bded
9 changed files with 128 additions and 93 deletions
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116
ltable.c
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@@ -350,9 +350,10 @@ int luaH_next (lua_State *L, Table *t, StkId key) {
unsigned int asize = luaH_realasize(t);
unsigned int i = findindex(L, t, s2v(key), asize); /* find original key */
for (; i < asize; i++) { /* try first array part */
if (!isempty(&t->array[i])) { /* a non-empty entry? */
int tag = *getArrTag(t, i + 1);
if (!tagisempty(tag)) { /* a non-empty entry? */
setivalue(s2v(key), i + 1);
setobj2s(L, key + 1, &t->array[i]);
farr2val(t, i + 1, tag, s2v(key + 1));
return 1;
}
}
@@ -374,6 +375,41 @@ static void freehash (lua_State *L, Table *t) {
}
/*
** Check whether an integer key is in the array part. If 'alimit' is
** not the real size of the array, the key still can be in the array
** part. In this case, do the "Xmilia trick" to check whether 'key-1'
** is smaller than the real size.
** The trick works as follow: let 'p' be an integer such that
** '2^(p+1) >= alimit > 2^p', or '2^(p+1) > alimit-1 >= 2^p'.
** That is, 2^(p+1) is the real size of the array, and 'p' is the highest
** bit on in 'alimit-1'. What we have to check becomes 'key-1 < 2^(p+1)'.
** We compute '(key-1) & ~(alimit-1)', which we call 'res'; it will
** have the 'p' bit cleared. If the key is outside the array, that is,
** 'key-1 >= 2^(p+1)', then 'res' will have some 1-bit higher than 'p',
** therefore it will be larger or equal to 'alimit', and the check
** will fail. If 'key-1 < 2^(p+1)', then 'res' has no 1-bit higher than
** 'p', and as the bit 'p' itself was cleared, 'res' will be smaller
** than 2^p, therefore smaller than 'alimit', and the check succeeds.
** As special cases, when 'alimit' is 0 the condition is trivially false,
** and when 'alimit' is 1 the condition simplifies to 'key-1 < alimit'.
** If key is 0 or negative, 'res' will have its higher bit on, so that
** if cannot be smaller than alimit.
*/
static int keyinarray (Table *t, lua_Integer key) {
lua_Unsigned alimit = t->alimit;
if (l_castS2U(key) - 1u < alimit) /* 'key' in [1, t->alimit]? */
return 1;
else if (!isrealasize(t) && /* key still may be in the array part? */
(((l_castS2U(key) - 1u) & ~(alimit - 1u)) < alimit)) {
t->alimit = cast_uint(key); /* probably '#t' is here now */
return 1;
}
else
return 0;
}
/*
** {=============================================================
** Rehash
@@ -421,6 +457,12 @@ static int countint (lua_Integer key, unsigned int *nums) {
}
l_sinline int arraykeyisempty (const Table *t, lua_Integer key) {
int tag = *getArrTag(t, key);
return tagisempty(tag);
}
/*
** Count keys in array part of table 't': Fill 'nums[i]' with
** number of keys that will go into corresponding slice and return
@@ -443,7 +485,7 @@ static unsigned int numusearray (const Table *t, unsigned int *nums) {
}
/* count elements in range (2^(lg - 1), 2^lg] */
for (; i <= lim; i++) {
if (!isempty(&t->array[i-1]))
if (!arraykeyisempty(t, i))
lc++;
}
nums[lg] += lc;
@@ -555,7 +597,7 @@ void luaH_resize (lua_State *L, Table *t, unsigned int newasize,
unsigned int i;
Table newt; /* to keep the new hash part */
unsigned int oldasize = setlimittosize(t);
TValue *newarray;
ArrayCell *newarray;
/* create new hash part with appropriate size into 'newt' */
setnodevector(L, &newt, nhsize);
if (newasize < oldasize) { /* will array shrink? */
@@ -563,14 +605,18 @@ void luaH_resize (lua_State *L, Table *t, unsigned int newasize,
exchangehashpart(t, &newt); /* and new hash */
/* re-insert into the new hash the elements from vanishing slice */
for (i = newasize; i < oldasize; i++) {
if (!isempty(&t->array[i]))
luaH_setint(L, t, i + 1, &t->array[i]);
int tag = *getArrTag(t, i + 1);
if (!tagisempty(tag)) { /* a non-empty entry? */
TValue aux;
farr2val(t, i + 1, tag, &aux);
luaH_setint(L, t, i + 1, &aux);
}
}
t->alimit = oldasize; /* restore current size... */
exchangehashpart(t, &newt); /* and hash (in case of errors) */
}
/* allocate new array */
newarray = luaM_reallocvector(L, t->array, oldasize, newasize, TValue);
newarray = luaM_reallocvector(L, t->array, oldasize, newasize, ArrayCell);
if (l_unlikely(newarray == NULL && newasize > 0)) { /* allocation failed? */
freehash(L, &newt); /* release new hash part */
luaM_error(L); /* raise error (with array unchanged) */
@@ -580,7 +626,7 @@ void luaH_resize (lua_State *L, Table *t, unsigned int newasize,
t->array = newarray; /* set new array part */
t->alimit = newasize;
for (i = oldasize; i < newasize; i++) /* clear new slice of the array */
setempty(&t->array[i]);
*getArrTag(t, i + 1) = LUA_VEMPTY;
/* re-insert elements from old hash part into new parts */
reinsert(L, &newt, t); /* 'newt' now has the old hash */
freehash(L, &newt); /* free old hash part */
@@ -719,41 +765,6 @@ void luaH_newkey (lua_State *L, Table *t, const TValue *key, TValue *value) {
}
/*
** Check whether key is in the array part. If 'alimit' is not the real
** size of the array, the key still can be in the array part. In this
** case, do the "Xmilia trick" to check whether 'key-1' is smaller than
** the real size.
** The trick works as follow: let 'p' be an integer such that
** '2^(p+1) >= alimit > 2^p', or '2^(p+1) > alimit-1 >= 2^p'.
** That is, 2^(p+1) is the real size of the array, and 'p' is the highest
** bit on in 'alimit-1'. What we have to check becomes 'key-1 < 2^(p+1)'.
** We compute '(key-1) & ~(alimit-1)', which we call 'res'; it will
** have the 'p' bit cleared. If the key is outside the array, that is,
** 'key-1 >= 2^(p+1)', then 'res' will have some 1-bit higher than 'p',
** therefore it will be larger or equal to 'alimit', and the check
** will fail. If 'key-1 < 2^(p+1)', then 'res' has no 1-bit higher than
** 'p', and as the bit 'p' itself was cleared, 'res' will be smaller
** than 2^p, therefore smaller than 'alimit', and the check succeeds.
** As special cases, when 'alimit' is 0 the condition is trivially false,
** and when 'alimit' is 1 the condition simplifies to 'key-1 < alimit'.
** If key is 0 or negative, 'res' will have its higher bit on, so that
** if cannot be smaller than alimit.
*/
static int keyinarray (Table *t, lua_Integer key) {
lua_Unsigned alimit = t->alimit;
if (l_castS2U(key) - 1u < alimit) /* 'key' in [1, t->alimit]? */
return 1;
else if (!isrealasize(t) && /* key still may be in the array part? */
(((l_castS2U(key) - 1u) & ~(alimit - 1u)) < alimit)) {
t->alimit = cast_uint(key); /* probably '#t' is here now */
return 1;
}
else
return 0;
}
static const TValue *getintfromhash (Table *t, lua_Integer key) {
Node *n = hashint(t, key);
lua_assert(l_castS2U(key) - 1u >= luaH_realasize(t));
@@ -770,15 +781,8 @@ static const TValue *getintfromhash (Table *t, lua_Integer key) {
}
l_sinline int arraykeyisempty (Table *t, lua_Integer key) {
int tag = *getArrTag(t, key);
return tagisempty(tag);
}
static int hashkeyisempty (Table *t, lua_Integer key) {
const TValue *val = getintfromhash(t, key);
lua_assert(!keyinarray(t, key));
return isempty(val);
}
@@ -797,7 +801,7 @@ int luaH_getint (Table *t, lua_Integer key, TValue *res) {
if (keyinarray(t, key)) {
int tag = *getArrTag(t, key);
if (!tagisempty(tag)) {
arr2val(t, key, tag, res);
farr2val(t, key, tag, res);
return HOK; /* success */
}
else
@@ -900,7 +904,7 @@ int luaH_psetint (Table *t, lua_Integer key, TValue *val) {
if (keyinarray(t, key)) {
lu_byte *tag = getArrTag(t, key);
if (!tagisempty(*tag)) {
val2arr(t, key, tag, val);
fval2arr(t, key, tag, val);
return HOK; /* success */
}
else
@@ -956,7 +960,7 @@ void luaH_finishset (lua_State *L, Table *t, const TValue *key,
}
else { /* array entry */
hres = ~hres; /* real index */
val2arr(t, hres, getArrTag(t, hres), value);
fval2arr(t, hres, getArrTag(t, hres), value);
}
}
@@ -1087,11 +1091,11 @@ lua_Unsigned luaH_getn (Table *t) {
/* 'limit' is zero or present in table */
if (!limitequalsasize(t)) { /* (2)? */
/* 'limit' > 0 and array has more elements after 'limit' */
if (isempty(&t->array[limit])) /* 'limit + 1' is empty? */
if (arraykeyisempty(t, limit + 1)) /* 'limit + 1' is empty? */
return limit; /* this is the boundary */
/* else, try last element in the array */
limit = luaH_realasize(t);
if (isempty(&t->array[limit - 1])) { /* empty? */
if (arraykeyisempty(t, limit)) { /* empty? */
/* there must be a boundary in the array after old limit,
and it must be a valid new limit */
unsigned int boundary = binsearch(t, t->alimit, limit);
@@ -1102,7 +1106,7 @@ lua_Unsigned luaH_getn (Table *t) {
}
/* (3) 'limit' is the last element and either is zero or present in table */
lua_assert(limit == luaH_realasize(t) &&
(limit == 0 || !isempty(&t->array[limit - 1])));
(limit == 0 || !arraykeyisempty(t, limit)));
if (isdummy(t) || hashkeyisempty(t, cast(lua_Integer, limit + 1)))
return limit; /* 'limit + 1' is absent */
else /* 'limit + 1' is also present */