py: Optimise call to mp_arg_check_num by compressing fun signature.

With 5 arguments to mp_arg_check_num(), some architectures need to pass
values on the stack.  So compressing n_args_min, n_args_max, takes_kw into
a single word and passing only 3 arguments makes the call more efficient,
because almost all calls to this function pass in constant values.  Code
size is also reduced by a decent amount:

   bare-arm:  -116
minimal x86:   -64
   unix x64:  -256
unix nanbox:  -112
      stm32:  -324
     cc3200:  -192
    esp8266:  -192
      esp32:  -144

1 files changed, 7 insertions, 7 deletions

diff --git a/py/obj.h b/py/obj.h
index f9bdb59d5..4a371bc63 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -277,6 +277,9 @@ typedef struct _mp_rom_obj_t { mp_const_obj_t o; } mp_rom_obj_t;
 #define MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(obj_name) extern const mp_obj_fun_builtin_var_t obj_name
 #define MP_DECLARE_CONST_FUN_OBJ_KW(obj_name) extern const mp_obj_fun_builtin_var_t obj_name
 
+#define MP_OBJ_FUN_ARGS_MAX (0xffff) // to set maximum value in n_args_max below
+#define MP_OBJ_FUN_MAKE_SIG(n_args_min, n_args_max, takes_kw) (((n_args_min) << 17) | ((n_args_max) << 1) | (takes_kw))
+
 #define MP_DEFINE_CONST_FUN_OBJ_0(obj_name, fun_name) \
     const mp_obj_fun_builtin_fixed_t obj_name = \
         {{&mp_type_fun_builtin_0}, .fun._0 = fun_name}
@@ -291,13 +294,13 @@ typedef struct _mp_rom_obj_t { mp_const_obj_t o; } mp_rom_obj_t;
         {{&mp_type_fun_builtin_3}, .fun._3 = fun_name}
 #define MP_DEFINE_CONST_FUN_OBJ_VAR(obj_name, n_args_min, fun_name) \
     const mp_obj_fun_builtin_var_t obj_name = \
-        {{&mp_type_fun_builtin_var}, false, n_args_min, MP_OBJ_FUN_ARGS_MAX, .fun.var = fun_name}
+        {{&mp_type_fun_builtin_var}, MP_OBJ_FUN_MAKE_SIG(n_args_min, MP_OBJ_FUN_ARGS_MAX, false), .fun.var = fun_name}
 #define MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(obj_name, n_args_min, n_args_max, fun_name) \
     const mp_obj_fun_builtin_var_t obj_name = \
-        {{&mp_type_fun_builtin_var}, false, n_args_min, n_args_max, .fun.var = fun_name}
+        {{&mp_type_fun_builtin_var}, MP_OBJ_FUN_MAKE_SIG(n_args_min, n_args_max, false), .fun.var = fun_name}
 #define MP_DEFINE_CONST_FUN_OBJ_KW(obj_name, n_args_min, fun_name) \
     const mp_obj_fun_builtin_var_t obj_name = \
-        {{&mp_type_fun_builtin_var}, true, n_args_min, MP_OBJ_FUN_ARGS_MAX, .fun.kw = fun_name}
+        {{&mp_type_fun_builtin_var}, MP_OBJ_FUN_MAKE_SIG(n_args_min, MP_OBJ_FUN_ARGS_MAX, true), .fun.kw = fun_name}
 
 // These macros are used to define constant map/dict objects
 // You can put "static" in front of the definition to make it local
@@ -785,12 +788,9 @@ typedef struct _mp_obj_fun_builtin_fixed_t {
     } fun;
 } mp_obj_fun_builtin_fixed_t;
 
-#define MP_OBJ_FUN_ARGS_MAX (0xffff) // to set maximum value in n_args_max below
 typedef struct _mp_obj_fun_builtin_var_t {
     mp_obj_base_t base;
-    bool is_kw : 1;
-    mp_uint_t n_args_min : 15; // inclusive
-    mp_uint_t n_args_max : 16; // inclusive
+    uint32_t sig; // see MP_OBJ_FUN_MAKE_SIG
     union {
         mp_fun_var_t var;
         mp_fun_kw_t kw;