Clone a lua table

lclonetable.c

// gcc -o clonetable.so --shared lclonetable.c -I$(LUAINCLUDE)

#include <lobject.h>
#include <ltable.h>
#include <lgc.h>
#include <lstate.h>
#include <lauxlib.h>
#include <lualib.h>
#include <lua.h>
#include <string.h>

#define black2gray(x)	resetbit(x->marked, BLACKBIT)
#define linkgclist(o,p)	((o)->gclist = (p), (p) = obj2gco(o))

static void
barrierback(lua_State *L, Table *t) {
	if (isblack(t)) {
		global_State *g = G(L);
		black2gray(t);  /* make table gray (again) */
		linkgclist(t, g->grayagain);
	}
}


// table.clone(to, from)
static int
lclonetable(lua_State *L) {
	luaL_checktype(L, 1, LUA_TTABLE);
	luaL_checktype(L, 2, LUA_TTABLE);
	Table * to = (Table *)lua_topointer(L, 1);
	const Table * from = lua_topointer(L, 2);
	void *ud;
	lua_Alloc alloc = lua_getallocf(L, &ud);
	if (from->lsizenode != to->lsizenode) {
		if (isdummy(from)) {
			// free to->node
			if (!isdummy(to))
				alloc(ud, to->node, sizenode(to) * sizeof(Node), 0);
			to->node = from->node;
		} else {
			unsigned int size = sizenode(from) * sizeof(Node);
			Node *node = alloc(ud, NULL, 0, size);
			if (node == NULL)
				luaL_error(L, "Out of memory");
			memcpy(node, from->node, size);
			// free to->node
			if (!isdummy(to))
				alloc(ud, to->node, sizenode(to) * sizeof(Node), 0);
			to->node = node;			
		}
		to->lsizenode = from->lsizenode;
	} else if (!isdummy(from)) {
		unsigned int size = sizenode(from) * sizeof(Node);
		if (isdummy(to)) {
			Node *node = alloc(ud, NULL, 0, size);
			if (node == NULL)
				luaL_error(L, "Out of memory");
			to->node = node;
		}
		memcpy(to->node, from->node, size);
	}
	if (from->lastfree) {
		int lastfree = from->lastfree - from->node;
		to->lastfree = to->node + lastfree;
	} else {
		to->lastfree = NULL;
	}
	if (from->sizearray != to->sizearray) {
		if (from->sizearray) {
			TValue *array = alloc(ud, NULL, 0, from->sizearray * sizeof(TValue));
			if (array == NULL)
				luaL_error(L, "Out of memory");
			alloc(ud, to->array, to->sizearray * sizeof(TValue), 0);
			to->array = array;
		} else {
			alloc(ud, to->array, to->sizearray * sizeof(TValue), 0);
			to->array = NULL;
		}
		to->sizearray = from->sizearray;
	}
	memcpy(to->array, from->array, from->sizearray * sizeof(TValue));
	barrierback(L,to);
	lua_settop(L, 1);
	return 1;
}

LUAMOD_API int
luaopen_clonetable(lua_State *L) {
	luaL_checkversion(L);
	luaL_requiref(L, "table", luaopen_table, 0);
	lua_pushcfunction(L, lclonetable);
	lua_setfield(L, -2, "clone");
	return 1;
}

/*
local table = require "clonetable"

a =  {x=1,y=2, 5,6,7}
table.clone(a, {1,2,3, z=4})

for k,v in pairs(a) do
	print(k,v)
end
*/