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commit c36ced53c92088748c278764acb68dfb66f353c9
parent d41c36bf67d6628bccd91697e7f88e55d40d3970
Author: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date:   Thu,  3 Dec 2020 12:00:05 -0300

Avoid "bad programming habits" in the reference system

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.

Diffstat:
Mlauxlib.c | 24++++++++++++++++++------
1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/lauxlib.c b/lauxlib.c @@ -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 */