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Avoid "bad programming habits" in the reference system

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References were using both 0 indices and nils as values in arrays.
Both do not fit in the concept of a sequence, which is the kind
of use that guides all Lua optimizations.
This commit is contained in:
Roberto Ierusalimschy 2020-12-03 12:00:32 -03:00
parent d41c36bf67
commit c36ced53c9
1 changed files with 18 additions and 6 deletions
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24
lauxlib.c
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@ -639,10 +639,14 @@ LUALIB_API char *luaL_buffinitsize (lua_State *L, luaL_Buffer *B, size_t sz) {
** =======================================================
*/
/* index of free-list header */
#define freelist 0
/* index of free-list header (after the predefined values) */
#define freelist (LUA_RIDX_LAST + 1)
/*
** The previously freed references form a linked list:
** t[freelist] is the index of a first free index, or zero if list is
** empty; t[t[freelist]] is the index of the second element; etc.
*/
LUALIB_API int luaL_ref (lua_State *L, int t) {
int ref;
if (lua_isnil(L, -1)) {
@ -650,9 +654,16 @@ LUALIB_API int luaL_ref (lua_State *L, int t) {
return LUA_REFNIL; /* 'nil' has a unique fixed reference */
}
t = lua_absindex(L, t);
lua_rawgeti(L, t, freelist); /* get first free element */
ref = (int)lua_tointeger(L, -1); /* ref = t[freelist] */
lua_pop(L, 1); /* remove it from stack */
if (lua_rawgeti(L, t, freelist) == LUA_TNIL) { /* first access? */
ref = 0; /* list is empty */
lua_pushinteger(L, 0); /* initialize as an empty list */
lua_rawseti(L, t, freelist); /* ref = t[freelist] = 0 */
}
else { /* already initialized */
lua_assert(lua_isinteger(L, -1));
ref = (int)lua_tointeger(L, -1); /* ref = t[freelist] */
}
lua_pop(L, 1); /* remove element from stack */
if (ref != 0) { /* any free element? */
lua_rawgeti(L, t, ref); /* remove it from list */
lua_rawseti(L, t, freelist); /* (t[freelist] = t[ref]) */
@ -668,6 +679,7 @@ LUALIB_API void luaL_unref (lua_State *L, int t, int ref) {
if (ref >= 0) {
t = lua_absindex(L, t);
lua_rawgeti(L, t, freelist);
lua_assert(lua_isinteger(L, -1));
lua_rawseti(L, t, ref); /* t[ref] = t[freelist] */
lua_pushinteger(L, ref);
lua_rawseti(L, t, freelist); /* t[freelist] = ref */