jsapi.c

// Code from here:
// https://github.com/jrmuizel/mozilla-cvs-history/blob/781c48087175615674b38b31fcc0aae17f0651b6/js/src/jsapi.h
// https://github.com/jrmuizel/mozilla-cvs-history/blob/781c48087175615674b38b31fcc0aae17f0651b6/js/src/jsapi.c

#include <stdio.h>

/*

// what is jsval?
// js/src/jspubtd.h
// line 36
typedef prword jsval;
// js/src/jscompat.h
// line 47
typedef prword_t prword;
// nsprpub/pr/include/obsolete/protypes.h
// line 76
typedef PRWord prword_t;
// nsprpub/pr/include/prtypes.h
// line 355
// ** A PRWord is an integer that is the same size as a void*
typedef long PRWord;
// Long signed integer type. Capable of containing at least the [−2147483647, +2147483647] range
// https://en.wikipedia.org/wiki/C_data_types

*/

typedef long jsval;
typedef unsigned int uint;

#define JSVAL_OBJECT 0x0  /* untagged reference to object */
#define JSVAL_INT 0x1     /* tagged 31-bit integer value */
#define JSVAL_DOUBLE 0x2  /* tagged reference to double */
#define JSVAL_STRING 0x4  /* tagged reference to string */
#define JSVAL_BOOLEAN 0x6 /* tagged boolean value */

#define PR_BIT(n) ((uint)1 << (n))
#define PR_BITMASK(n) (PR_BIT(n) - 1)
#define JSVAL_TAGMASK PR_BITMASK(JSVAL_TAGBITS)
#define JSVAL_TAG(v) ((v) & JSVAL_TAGMASK)
#define JSVAL_TAGBITS 3
#define JSVAL_IS_NULL(v) ((v) == JSVAL_NULL)
#define JSVAL_NULL OBJECT_TO_JSVAL(0)
#define OBJECT_TO_JSVAL(obj) ((jsval)(obj))

#define JSVAL_IS_OBJECT(v) (JSVAL_TAG(v) == JSVAL_OBJECT)
#define JSVAL_VOID INT_TO_JSVAL(0 - JSVAL_INT_POW2(30))
#define JSVAL_IS_VOID(v) ((v) == JSVAL_VOID)
#define INT_TO_JSVAL(i) (((jsval)(i) << 1) | JSVAL_INT)
#define JSVAL_INT_POW2(n) ((jsval)1 << (n))

/* Type tag bitfield length and derived macros. */
#define JSVAL_TAGBITS 3
#define JSVAL_TAGMASK PR_BITMASK(JSVAL_TAGBITS)
#define JSVAL_TAG(v) ((v) & JSVAL_TAGMASK)
#define JSVAL_SETTAG(v, t) ((v) | (t))
#define JSVAL_CLRTAG(v) ((v) & ~(jsval)JSVAL_TAGMASK)
#define JSVAL_ALIGN PR_BIT(JSVAL_TAGBITS)

#define JSVAL_TO_GCTHING(v) ((void *)JSVAL_CLRTAG(v))
#define JSVAL_TO_OBJECT(v) ((JSObject *)JSVAL_TO_GCTHING(v))

/* Predicates for type testing. */
#define JSVAL_IS_OBJECT(v) (JSVAL_TAG(v) == JSVAL_OBJECT)
#define JSVAL_IS_NUMBER(v) (JSVAL_IS_INT(v) || JSVAL_IS_DOUBLE(v))
#define JSVAL_IS_INT(v) (((v) & JSVAL_INT) && (v) != JSVAL_VOID)
#define JSVAL_IS_DOUBLE(v) (JSVAL_TAG(v) == JSVAL_DOUBLE)
#define JSVAL_IS_STRING(v) (JSVAL_TAG(v) == JSVAL_STRING)
#define JSVAL_IS_BOOLEAN(v) (JSVAL_TAG(v) == JSVAL_BOOLEAN)
#define JSVAL_IS_NULL(v) ((v) == JSVAL_NULL)
#define JSVAL_IS_VOID(v) ((v) == JSVAL_VOID)

struct JSClass
{
};

typedef struct JSClass JSClass;

struct JSContext
{
};

typedef struct JSContext JSContext;

struct JSObjectMap
{
  JSClass *clasp;
};

typedef struct JSObjectMap JSObjectMap;

struct JSObject
{
  JSObjectMap *map;
};

typedef struct JSObject JSObject;

JSClass js_FunctionClass = {};

/* Typeof operator result enumeration. */
typedef enum JSType
{
  JSTYPE_VOID,     /* undefined */
  JSTYPE_OBJECT,   /* object */
  JSTYPE_FUNCTION, /* function */
  JSTYPE_STRING,   /* string */
  JSTYPE_NUMBER,   /* number */
  JSTYPE_BOOLEAN,  /* boolean */
  JSTYPE_NULL,
  JSTYPE_LIMIT
} JSType;

/*
 * Keep this in sync with jspubtd.h -- an assertion below will insist that
 * its length match the JSType enum's JSTYPE_LIMIT limit value.
 */
char *js_type_str[] = {
    "undefined",
    "object",
    "function",
    "string",
    "number",
    "boolean",
    "null"};

char *JS_GetTypeName(JSType type)
{
  if ((uint)type >= (uint)JSTYPE_LIMIT)
    return NULL;
  return js_type_str[type];
}

JSType JS_TypeOfValue(jsval v)
{
  JSType type;
  JSObject *obj;

  if (JSVAL_IS_NULL(v))
  {
    type = JSTYPE_NULL;
  }
  else if (JSVAL_IS_VOID(v))
  {
    type = JSTYPE_VOID;
  }
  else if (JSVAL_IS_OBJECT(v))
  {
    obj = JSVAL_TO_OBJECT(v);
    if (obj &&
        (obj->map->clasp == &js_FunctionClass))
    {
      type = JSTYPE_FUNCTION;
    }
  }
  else if (JSVAL_IS_NUMBER(v))
  {
    type = JSTYPE_NUMBER;
  }
  else if (JSVAL_IS_STRING(v))
  {
    type = JSTYPE_STRING;
  }
  else if (JSVAL_IS_BOOLEAN(v))
  {
    type = JSTYPE_BOOLEAN;
  }
  return type;
}

int main()
{
  jsval value = JSVAL_NULL;
  JSType type = JS_TypeOfValue(value);
  char *typeName = JS_GetTypeName(type);

  printf("type: %s\n", typeName);

  if (value == NULL) {
      printf("value points to NULL\n");
  }

  return 0;
}