py: Implement sys.maxsize, standard way to check platform "bitness".

Implementing it as a static constant is a bit peculiar and require cooperation
from long int implementation.

py/modsys.c

@@ -24,6 +24,8 @@
  * THE SOFTWARE.
  */
 
+#include <stdint.h>
+#include <limits.h>
 #include "mpconfig.h"
 #include "misc.h"
 #include "qstr.h"
@@ -33,6 +35,8 @@
 #include "objlist.h"
 #include "objtuple.h"
 #include "objstr.h"
+#include "mpz.h"
+#include "objint.h"
 
 #if MICROPY_PY_SYS
 
@@ -44,6 +48,8 @@ extern struct _dummy_t mp_sys_stdin_obj;
 extern struct _dummy_t mp_sys_stdout_obj;
 extern struct _dummy_t mp_sys_stderr_obj;
 
+extern mp_obj_int_t mp_maxsize_obj;
+
 mp_obj_list_t mp_sys_path_obj;
 mp_obj_list_t mp_sys_argv_obj;
 #define I(n) MP_OBJ_NEW_SMALL_INT(n)
@@ -70,6 +76,19 @@ STATIC const mp_map_elem_t mp_module_sys_globals_table[] = {
 #else
     { MP_OBJ_NEW_QSTR(MP_QSTR_byteorder), MP_OBJ_NEW_QSTR(MP_QSTR_big) },
 #endif
+#if MICROPY_PY_SYS_MAXSIZE
+    #if MICROPY_LONGINT_IMPL == MICROPY_LONGINT_IMPL_NONE
+    // INT_MAX is not representable as small int, as we know that small int
+    // takes one bit for tag. So, we have little choice but to provide this
+    // value. Apps also should be careful to not try to compare sys.maxsize
+    // with some number (which may not fit in available int size), but instead
+    // count number of significant bits in sys.maxsize.
+    { MP_OBJ_NEW_QSTR(MP_QSTR_maxsize), MP_OBJ_NEW_SMALL_INT(INT_MAX >> 1) },
+    #else
+    { MP_OBJ_NEW_QSTR(MP_QSTR_maxsize), (mp_obj_t)&mp_maxsize_obj },
+    #endif
+#endif
+
 
 #if MICROPY_PY_SYS_EXIT
     { MP_OBJ_NEW_QSTR(MP_QSTR_exit), (mp_obj_t)&mp_sys_exit_obj },

py/mpconfig.h

@@ -336,6 +336,11 @@ typedef double mp_float_t;
 #define MICROPY_PY_SYS (1)
 #endif
 
+// Whether to provide "sys.maxsize" constant
+#ifndef MICROPY_PY_SYS_MAXSIZE
+#define MICROPY_PY_SYS_MAXSIZE (0)
+#endif
+
 // Whether to provide "sys.exit" function
 #ifndef MICROPY_PY_SYS_EXIT
 #define MICROPY_PY_SYS_EXIT (0)

py/objint_longlong.c

@@ -50,6 +50,11 @@
 #define SUFFIX ""
 #endif
 
+#if MICROPY_PY_SYS_MAXSIZE
+// Export value for sys.maxsize
+const mp_obj_int_t mp_maxsize_obj = {{&mp_type_int}, INT_MAX};
+#endif
+
 bool mp_obj_int_is_positive(mp_obj_t self_in) {
     if (MP_OBJ_IS_SMALL_INT(self_in)) {
         return MP_OBJ_SMALL_INT_VALUE(self_in) >= 0;

py/objint_mpz.c

@@ -43,6 +43,26 @@
 
 #if MICROPY_LONGINT_IMPL == MICROPY_LONGINT_IMPL_MPZ
 
+#if MICROPY_PY_SYS_MAXSIZE
+// Export value for sys.maxsize
+#define DIG_MASK ((1 << MPZ_DIG_SIZE) - 1)
+STATIC const mpz_dig_t maxsize_dig[MPZ_NUM_DIG_FOR_INT] = {
+    (INT_MAX >> MPZ_DIG_SIZE * 0) & DIG_MASK,
+    (INT_MAX >> MPZ_DIG_SIZE * 1) & DIG_MASK,
+    (INT_MAX >> MPZ_DIG_SIZE * 2) & DIG_MASK,
+    #if (INT_MAX >> MPZ_DIG_SIZE * 2) > DIG_MASK
+    (INT_MAX >> MPZ_DIG_SIZE * 3) & DIG_MASK,
+    (INT_MAX >> MPZ_DIG_SIZE * 4) & DIG_MASK,
+//    (INT_MAX >> MPZ_DIG_SIZE * 5) & DIG_MASK,
+    #endif
+};
+const mp_obj_int_t mp_maxsize_obj = {
+    {&mp_type_int},
+    {.fixed_dig = 1, .len = MPZ_NUM_DIG_FOR_INT, .alloc = MPZ_NUM_DIG_FOR_INT, .dig = (mpz_dig_t*)maxsize_dig}
+};
+#undef DIG_MASK
+#endif
+
 STATIC mp_obj_int_t *mp_obj_int_new_mpz(void) {
     mp_obj_int_t *o = m_new_obj(mp_obj_int_t);
     o->base.type = &mp_type_int;

py/qstrdefs.h

@@ -352,6 +352,9 @@ Q(stdout)
 Q(stderr)
 Q(version)
 Q(version_info)
+#if MICROPY_PY_SYS_MAXSIZE
+Q(maxsize)
+#endif
 #endif
 
 #if MICROPY_PY_STRUCT

unix/mpconfigport.h

@@ -45,6 +45,7 @@
 #define MICROPY_PY_BUILTINS_FROZENSET (1)
 #define MICROPY_PY_SYS_EXIT         (1)
 #define MICROPY_PY_SYS_PLATFORM     "linux"
+#define MICROPY_PY_SYS_MAXSIZE      (1)
 #define MICROPY_PY_SYS_STDFILES     (1)
 #define MICROPY_PY_CMATH            (1)
 #define MICROPY_PY_IO_FILEIO        (1)