static TValue *index2addr (lua_State *L, int idx) {
CallInfo *ci = L->ci;
if (idx > 0) {
TValue *o = ci->func + idx;
api_check(L, idx <= ci->top - (ci->func + 1), "unacceptable index");
if (o >= L->top) return NONVALIDVALUE;
else return o;
}
else if (!ispseudo(idx)) { /* negative index */
api_check(L, idx != 0 && -idx <= L->top - (ci->func + 1), "invalid index");
return L->top + idx;
}
else if (idx == LUA_REGISTRYINDEX)
return &G(L)->l_registry;
else { /* upvalues */
idx = LUA_REGISTRYINDEX - idx;
api_check(L, idx <= MAXUPVAL + 1, "upvalue index too large");
if (ttislcf(ci->func)) /* light C function? */
return NONVALIDVALUE; /* it has no upvalues */
else {
CClosure *func = clCvalue(ci->func);
return (idx <= func->nupvalues) ? &func->upvalue[idx-1] : NONVALIDVALUE;
}
}
}
/*
** convert an acceptable stack index into an absolute index
*/
LUA_API int lua_absindex (lua_State *L, int idx) {
return (idx > 0 || ispseudo(idx))
? idx
: cast_int(L->top - L->ci->func + idx);
}
/*
** convert an acceptable stack index into an absolute index
*/
LUA_API int lua_absindex (lua_State *L, int idx) {
return (idx > 0 || ispseudo(idx)) //如果是大于0的索引，或者是伪索引
? idx
: cast_int(L->top - L->ci->func + idx);
//如果是小于0的索引，获取第一个空白-函数的偏移量+idx,则计算出的是一个正数的idx
}