c/lua:extraspace

c/lua/_demo/extraspace/extraspace.go

@@ -0,0 +1,42 @@
+package main
+
+import (
+	"unsafe"
+	_ "unsafe"
+
+	"github.com/goplus/llgo/c"
+	"github.com/goplus/llgo/c/lua"
+)
+
+func GetData(L *lua.State) c.Int {
+	extra := (*int)(L.Getextraspace())
+	L.Pushfstring(c.Str("Stored integer is: %d"), *extra)
+	return 1
+}
+
+func main() {
+	L := lua.Newstate__1()
+	defer L.Close()
+
+	L.Openlibs()
+
+	extra := (*int)(L.Getextraspace())
+	*extra = 42
+
+	difference := uintptr(unsafe.Pointer(L)) - uintptr(L.Getextraspace())
+	if difference == unsafe.Sizeof(uintptr(0)) {
+		c.Printf(c.Str("Extra space is pointer size\n"), unsafe.Sizeof(uintptr(0)))
+	}
+
+	L.Pushcfunction(GetData)
+	L.Setglobal(c.Str("GetData"))
+
+	if L.Dostring(c.Str("print(GetData())")) != lua.OK {
+		c.Printf(c.Str("Error: %s\n"), L.Tostring(-1))
+	}
+}
+
+/* Expected output:
+Extra space is pointer size
+Stored integer is: 42
+*/

c/lua/lua.go

@@ -460,7 +460,9 @@ func (L *State) Closeslot(idx c.Int) {}
  ** ===============================================================
  */
 
-// #define lua_getextraspace(L)	((void *)((char *)(L) - LUA_EXTRASPACE))
+func (L *State) Getextraspace() c.Pointer {
+	return c.Pointer(uintptr(c.Pointer(L)) - EXTRASPACE)
+}
 func (L *State) Tonumber(idx c.Int) Number   { return L.Tonumberx(idx, nil) }
 func (L *State) Tostring(idx c.Int) *c.Char  { return L.Tolstring(idx, nil) }
 func (L *State) Tointeger(idx c.Int) Integer { return L.Tointegerx(idx, nil) }

c/lua/luaconf.go

@@ -1,5 +1,7 @@
 package lua
 
+import "unsafe"
+
 /*
 ** {==================================================================
 ** Macros that affect the API and must be stable (that is, must be the
@@ -20,6 +22,15 @@ const (
 	MAXSTACK = 1000000
 )
 
+/*
+@@ LUA_EXTRASPACE defines the size of a raw memory area associated with
+** a Lua state with very fast access.
+** CHANGE it if you need a different size.
+*/
+const (
+	EXTRASPACE = unsafe.Sizeof(uintptr(0))
+)
+
 /*
 @@ LUA_IDSIZE gives the maximum size for the description of the source
 ** of a function in debug information.