Analysis of lua source code

This article is a navigation class , For the time being, let's start with something , Follow up to add slowly

Tips：LUA call C Language interface

• demand ：C Language programming interface , Export to LUA call
• C Interface form ：typedef int (lua_CFunction)(lua_State L)
• give an example ：int add(lua_State* L), That is, the return value must be int type , There is only one parameter and it is lua_State Pointer types
• lua_State：L by LUA call C Interface , adopt L Class interface of / Member variables are accessible LUA related data
• Input parameter acquisition method ： adopt L Pointer export method , Such as luaL_checknumber(L,1); Check the validity of the parameter and return the first input parameter ( From left to right )
• Output parameter transfer mode ： Pass the output value by pressing the stack , Such as ：lua_pushnumber(L,op1 + op2), And press a few parameters into the stack return A few , send LUA The stack can be balanced correctly

LUA Source reading notes (ver: 5.3.4)

Start with a function LUA Implementation mechanism , Some of the deeper content will produce a separate chapter , Such as ：TValue structure …
The source code reading starts with the mathematical calculation library

1. lmathlib.c
   use C Language implements some mathematical calculation class function interfaces , for LUA call , Analyze a ABS function , understand LUA Data interface and usage of , as follows ：

//  Derived function for finding absolute value 
static int math_abs (lua_State *L) {
    	// Conform to the export interface format convention 
  if (lua_isinteger(L, 1)) {
    
    lua_Integer n = lua_tointeger(L, 1);
    if (n < 0) n = (lua_Integer)(0u - (lua_Unsigned)n);
    lua_pushinteger(L, n);
  }
  else
    lua_pushnumber(L, l_mathop(fabs)(luaL_checknumber(L, 1)));
  return 1;
}

//  Which calls lua_isinteger Determine the input parameter type , Its function is implemented as ：
LUA_API int lua_isinteger (lua_State *L, int idx) {
    
  const TValue *o = index2value(L, idx);
  return ttisinteger(o);
}

//  among ttisinterger(0) Define... For macros , The expansion process of combined parameters is ：
#define ttisinteger(o) checktag((o), LUA_VNUMINT)
#define ttisinteger(o) checktag((o), makevariant(LUA_TNUMBER, 0)) // among LUA_TNUMBER by 3
#define ttisinteger(o) checktag(o, 3)
#define ttisinteger(o) o->tt_ == 3 // among o The type of TValue

One can basically guess TValue There is a member variable in the structure tt_ Represents the type of variable , among 3 yes int The enumerated values , of TValue For detailed analysis, see ：LUA TValue structure .（ It is suggested to read and play this article before continuing ）

go back to lua_isinteger Function , Find out about it TValue Type of o Variables are defined by functions index2value Call returned , See its implementation as follows ：

static TValue *index2value (lua_State *L, int idx) {
    
  CallInfo *ci = L->ci;
  if (idx > 0) {
    
    StkId o = ci->func + idx;
    api_check(L, idx <= L->ci->top - (ci->func + 1), "unacceptable index");
    if (o >= L->top) return &G(L)->nilvalue;	// Out of stack space return nil empty 
    else return s2v(o);
  }
  else{
    
  	...//ID<=0 For the time being , It can be understood as wrong call 
  }
}

//api_check Define... For macros , The expansion process of combined parameters is ：
#define api_check(l,e,msg) luai_apicheck(l,(e) && msg)
#define api_check(l,e,msg) luai_apicheck(L,(1 <= L->ci->top - (ci->func + 1) && "unacceptable index")
#define api_check(l,e,msg) luai_apicheck(L,(1 <=  The maximum number of parameters supported by the stack space ) && "unacceptable index") 
#define api_check(l,e,msg) (L, lua_assert(1)) / (L, lua_assert(0))

/* convert a 'StackValue' to a 'TValue' */
#define s2v(o) (&(o)->val)

You can basically guess ci->func Pointer to the top of the stack , adopt +idx To find the address of the input parameter , Through s2v obtain TValue
api_check It is responsible for checking whether the input parameters requested for access exceed the stack space , Prevent illegal access to data
among CallInfo structure ,StkId See the link for structure analysis ：LUA CallInfo structure ,StkId Structural analysis .（ It is suggested to read and play this article before continuing ）

go back to math_abs Function , Where the parameter is called lua_tointeger function

lua_Integer n = lua_tointeger(L, 1);
 And 
#define lua_tointeger(L,i) lua_tointegerx(L,(i),NULL)
LUA_API lua_Integer lua_tointegerx (lua_State *L, int idx, int *pisnum) {
    
  lua_Integer res = 0;
  const TValue *o = index2value(L, idx);
  int isnum = tointeger(o, &res);
  if (pisnum)
    *pisnum = isnum;
  return res;
}
 namely lua_tointeger(L, 1) == lua_tointegerx (L, 1, NULL)
index2value The function has been parsed above , The function is to specify... In the stack structure by serial number ID Data extraction , Here we take the first parameter 
 here tointeger(o, &res)  Equivalent to  (o)->tt_ == 3 ? (*(&res) = (((o)->value_).i), 1) : luaV_tointeger(o,&res,F2Ieq))
 There will be tt_ Is it 3 The judgment of the , Because in this version LUA take int and float Values are stored in lua_Integer in , So a distinction needs to be made here 

3. lstrlib.c
4. lapi.c
5. lobject.h