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Annotate Lua packer with more comments
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@ -70,6 +70,7 @@ static inline bool uses_union(int type)
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}
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}
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// can set_into be used with these key / value types in principle?
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static inline bool can_set_into(int ktype, int vtype)
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{
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switch (ktype) {
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@ -82,7 +83,7 @@ static inline bool can_set_into(int ktype, int vtype)
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}
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}
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// is the key suitable for use with set_into?
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// is the actual key suitable for use with set_into?
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static inline bool suitable_key(lua_State *L, int idx)
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{
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if (lua_type(L, idx) == LUA_TSTRING) {
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@ -143,6 +144,13 @@ namespace {
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typedef std::pair<std::string, Packer> PackerTuple;
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}
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/**
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* Append instruction to end.
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*
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* @param pv target
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* @param type instruction type
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* @return reference to instruction
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*/
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static inline auto emplace(PackedValue &pv, s16 type)
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{
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pv.i.emplace_back();
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@ -211,6 +219,13 @@ void script_register_packer(lua_State *L, const char *regname,
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lua_pop(L, 1);
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}
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/**
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* Find a packer for a metatable.
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*
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* @param regname metatable name
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* @param out packer will be placed here
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* @return success
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*/
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static bool find_packer(const char *regname, PackerTuple &out)
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{
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MutexAutoLock autolock(g_packers_lock);
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@ -223,6 +238,14 @@ static bool find_packer(const char *regname, PackerTuple &out)
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return true;
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}
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/**
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* Find a packer matching the metatable of the Lua value.
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*
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* @param L Lua state
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* @param idx Index on stack
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* @param out packer will be placed here
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* @return success
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*/
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static bool find_packer(lua_State *L, int idx, PackerTuple &out)
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{
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#ifndef NDEBUG
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@ -254,6 +277,21 @@ static bool find_packer(lua_State *L, int idx, PackerTuple &out)
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// Packing implementation
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//
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/**
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* Keeps track of seen objects, which is needed to make circular references work.
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* The first time an object is seen it remembers the instruction index.
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* The caller is expected to add instructions that produce the value immediately after.
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* For second, third, ... calls it pushes an instruction that references the already
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* created value.
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*
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* @param L Lua state
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* @param idx Index of value on Lua stack
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* @param pv target
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* @param seen Map of seen objects
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* @return empty reference (first time) or reference to instruction that
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* reproduces the value (otherwise)
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*
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*/
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static VectorRef<PackedInstr> record_object(lua_State *L, int idx, PackedValue &pv,
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std::unordered_map<const void *, s32> &seen)
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{
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@ -261,18 +299,31 @@ static VectorRef<PackedInstr> record_object(lua_State *L, int idx, PackedValue &
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assert(ptr);
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auto found = seen.find(ptr);
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if (found == seen.end()) {
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// first time, record index
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assert(pv.i.size() <= S32_MAX);
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seen[ptr] = pv.i.size();
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return VectorRef<PackedInstr>();
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}
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s32 ref = found->second;
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assert(ref < (s32)pv.i.size());
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// reuse the value from first time
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auto r = emplace(pv, INSTR_PUSHREF);
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r->ref = ref;
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r->sidata1 = ref;
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pv.i[ref].keep_ref = true;
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return r;
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}
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/**
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* Pack a single Lua value and add it to the instruction stream.
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*
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* @param L Lua state
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* @param idx Index of value on Lua stack. Must be positive, use absidx if not!
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* @param vidx Next free index on the stack as it would look during unpacking. (v = virtual)
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* @param pv target
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* @param seen Map of seen objects (see record_object)
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* @return reference to the instruction that creates the value
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*/
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static VectorRef<PackedInstr> pack_inner(lua_State *L, int idx, int vidx, PackedValue &pv,
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std::unordered_map<const void *, s32> &seen)
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{
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@ -330,6 +381,7 @@ static VectorRef<PackedInstr> pack_inner(lua_State *L, int idx, int vidx, Packed
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PackerTuple ser;
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if (!find_packer(L, idx, ser))
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throw LuaError("Cannot serialize unsupported userdata");
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// use packer callback to turn into a void*
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pv.contains_userdata = true;
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r = emplace(pv, LUA_TUSERDATA);
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r->sdata = ser.first;
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@ -358,22 +410,28 @@ static VectorRef<PackedInstr> pack_inner(lua_State *L, int idx, int vidx, Packed
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else
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rtable->uidata2++; // nrec
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// check if we can use a shortcut
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// set_into is a shortcut that allows a pushed value
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// to be directly set into a table without separately pushing
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// the key and using SETTABLE.
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// only works in certain circumstances, hence the check:
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if (can_set_into(ktype, vtype) && suitable_key(L, -2)) {
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// push only the value
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auto rval = pack_inner(L, absidx(L, -1), vidx, pv, seen);
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vidx++;
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rval->pop = rval->type != LUA_TTABLE;
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// and where to put it:
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// where to put it:
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rval->set_into = vi_table;
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if (ktype == LUA_TSTRING)
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rval->sdata = lua_tostring(L, -2);
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else
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rval->sidata1 = lua_tointeger(L, -2);
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// pop tables after the fact
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// since tables take multiple instructions to populate we have to
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// pop them separately afterwards.
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if (!rval->pop) {
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auto ri1 = emplace(pv, INSTR_POP);
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ri1->sidata1 = vidx;
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ri1->sidata1 = vidx - 1;
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}
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vidx--;
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} else {
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// push the key and value
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pack_inner(L, absidx(L, -2), vidx, pv, seen);
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@ -392,6 +450,7 @@ static VectorRef<PackedInstr> pack_inner(lua_State *L, int idx, int vidx, Packed
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lua_pop(L, 1);
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}
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// exactly the table should be left on stack
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assert(vidx == vi_table + 1);
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return rtable;
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}
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@ -405,6 +464,7 @@ PackedValue *script_pack(lua_State *L, int idx)
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std::unordered_map<const void *, s32> seen;
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pack_inner(L, idx, 1, pv, seen);
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// allocate last for exception safety
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return new PackedValue(std::move(pv));
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}
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@ -414,14 +474,15 @@ PackedValue *script_pack(lua_State *L, int idx)
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void script_unpack(lua_State *L, PackedValue *pv)
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{
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lua_newtable(L); // table at index top to track ref indices -> objects
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// table that tracks objects for keep_ref / PUSHREF (key = instr index)
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lua_newtable(L);
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const int top = lua_gettop(L);
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int ctr = 0;
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for (size_t packed_idx = 0; packed_idx < pv->i.size(); packed_idx++) {
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auto &i = pv->i[packed_idx];
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// If leaving values on stack make sure there's space (every 5th iteration)
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// Make sure there's space on the stack (if applicable)
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if (!i.pop && (ctr++) >= 5) {
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lua_checkstack(L, 5);
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ctr = 0;
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@ -449,7 +510,8 @@ void script_unpack(lua_State *L, PackedValue *pv)
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lua_remove(L, top + i.sidata2);
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continue;
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case INSTR_PUSHREF:
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lua_pushinteger(L, i.ref);
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// retrieve from top table
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lua_pushinteger(L, i.sidata1);
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lua_rawget(L, top);
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break;
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@ -476,7 +538,7 @@ void script_unpack(lua_State *L, PackedValue *pv)
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PackerTuple ser;
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sanity_check(find_packer(i.sdata.c_str(), ser));
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ser.second.fout(L, i.ptrdata);
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i.ptrdata = nullptr; // ownership taken by callback
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i.ptrdata = nullptr; // ownership taken by packer callback
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break;
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}
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@ -486,13 +548,14 @@ void script_unpack(lua_State *L, PackedValue *pv)
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}
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if (i.keep_ref) {
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// remember in top table
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lua_pushinteger(L, packed_idx);
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lua_pushvalue(L, -2);
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lua_rawset(L, top);
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}
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if (i.set_into) {
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if (!i.pop)
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if (!i.pop) // set will consume
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lua_pushvalue(L, -1);
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if (uses_sdata(i.type))
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lua_rawseti(L, top + i.set_into, i.sidata1);
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@ -504,7 +567,7 @@ void script_unpack(lua_State *L, PackedValue *pv)
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}
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}
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// as part of the unpacking process we take ownership of all userdata
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// as part of the unpacking process all userdata is "used up"
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pv->contains_userdata = false;
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// leave exactly one value on the stack
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lua_settop(L, top+1);
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@ -523,7 +586,7 @@ PackedValue::~PackedValue()
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if (i.type == LUA_TUSERDATA && i.ptrdata) {
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PackerTuple ser;
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if (find_packer(i.sdata.c_str(), ser)) {
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// tell it to deallocate object
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// tell packer to deallocate object
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ser.second.fout(nullptr, i.ptrdata);
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} else {
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assert(false);
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@ -536,7 +599,6 @@ PackedValue::~PackedValue()
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// script_dump_packed
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//
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#ifndef NDEBUG
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void script_dump_packed(const PackedValue *val)
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{
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printf("instruction stream: [\n");
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@ -550,7 +612,7 @@ void script_dump_packed(const PackedValue *val)
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printf(i.sidata2 ? "POP(%d, %d)" : "POP(%d)", i.sidata1, i.sidata2);
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break;
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case INSTR_PUSHREF:
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printf("PUSHREF(%d)", i.ref);
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printf("PUSHREF(%d)", i.sidata1);
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break;
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case LUA_TNIL:
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printf("nil");
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@ -593,4 +655,3 @@ void script_dump_packed(const PackedValue *val)
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}
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printf("]\n");
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}
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#endif
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@ -39,30 +39,31 @@ extern "C" {
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#define INSTR_PUSHREF (-12)
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/**
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* Represents a single instruction that pushes a new value or works with existing ones.
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* Represents a single instruction that pushes a new value or operates with existing ones.
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*/
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struct PackedInstr
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{
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s16 type; // LUA_T* or INSTR_*
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u16 set_into; // set into table on stack
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bool keep_ref; // is referenced later by INSTR_PUSHREF?
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bool keep_ref; // referenced later by INSTR_PUSHREF?
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bool pop; // remove from stack?
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// Note: the remaining members are named by type, not usage
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union {
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bool bdata; // boolean: value
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lua_Number ndata; // number: value
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struct {
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u16 uidata1, uidata2; // table: narr, nrec
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u16 uidata1, uidata2; // table: narr | nrec
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};
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struct {
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/*
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SETTABLE: key index, value index
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SETTABLE: key index | value index
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POP: indices to remove
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otherwise w/ set_into: numeric key, -
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PUSHREF: index of referenced instr | unused
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otherwise w/ set_into: numeric key | unused
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*/
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s32 sidata1, sidata2;
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};
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void *ptrdata; // userdata: implementation defined
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s32 ref; // PUSHREF: index of referenced instr
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};
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/*
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- string: value
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@ -78,7 +79,7 @@ struct PackedInstr
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/**
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* A packed value can be a primitive like a string or number but also a table
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* including all of its contents. It is made up of a linear stream of
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* 'instructions' that build the final value when executed.
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* instructions that build the final value when executed.
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*/
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struct PackedValue
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{
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