core: add int.bit_length() when MICROPY_CYPTHON_COMPAT is enabled

This method of integer objects is needed for a port of python3's
decimal.py module.

MICROPY_CPYTHON_COMPAT is enabled by CIRCUITPY_FULL_BUILD.

py/mpz.h

@@ -135,6 +135,9 @@ void mpz_xor_inpl(mpz_t *dest, const mpz_t *lhs, const mpz_t *rhs);
 void mpz_divmod_inpl(mpz_t *dest_quo, mpz_t *dest_rem, const mpz_t *lhs, const mpz_t *rhs);
 
 static inline size_t mpz_max_num_bits(const mpz_t *z) { return z->len * MPZ_DIG_SIZE; }
+static inline size_t mpz_num_bits(const mpz_t *z) {
+    size_t last_bits = (8 * (sizeof(long) - sizeof(mpz_dig_t))) - __builtin_clzl(z->dig[z->len-1]);
+    return z->len * MPZ_DIG_SIZE + last_bits; }
 mp_int_t mpz_hash(const mpz_t *z);
 bool mpz_as_int_checked(const mpz_t *z, mp_int_t *value);
 bool mpz_as_uint_checked(const mpz_t *z, mp_uint_t *value);

py/objint.c

@@ -457,6 +457,28 @@ mp_obj_t mp_obj_int_binary_op_extra_cases(mp_binary_op_t op, mp_obj_t lhs_in, mp
     return MP_OBJ_NULL; // op not supported
 }
 
+#if MICROPY_CPYTHON_COMPAT
+STATIC mp_obj_t int_bit_length(mp_obj_t self_in) {
+    #if MICROPY_LONGINT_IMPL != MICROPY_LONGINT_IMPL_NONE
+    if (!MP_OBJ_IS_SMALL_INT(self_in)) {
+        return mp_obj_int_bit_length_impl(self_in);
+    }
+    else
+    #endif
+    {
+        mp_int_t int_val = MP_OBJ_SMALL_INT_VALUE(self_in);
+        mp_uint_t value =
+            (int_val == 0) ? 0 :
+            (int_val == MP_SMALL_INT_MIN) ? 8 * sizeof(mp_int_t) :
+            (int_val < 0) ? 8 * sizeof(long) - __builtin_clzl(-int_val) :
+                 8 * sizeof(long) - __builtin_clzl(int_val);
+        return mp_obj_new_int_from_uint(value);
+    }
+
+}
+MP_DEFINE_CONST_FUN_OBJ_1(int_bit_length_obj, int_bit_length);
+#endif
+
 // this is a classmethod
 STATIC mp_obj_t int_from_bytes(size_t n_args, const mp_obj_t *args) {
     // TODO: Support signed param (assumes signed=False at the moment)
@@ -537,6 +559,9 @@ STATIC mp_obj_t int_to_bytes(size_t n_args, const mp_obj_t *pos_args, mp_map_t *
 STATIC MP_DEFINE_CONST_FUN_OBJ_KW(int_to_bytes_obj, 3, int_to_bytes);
 
 STATIC const mp_rom_map_elem_t int_locals_dict_table[] = {
+#if MICROPY_CPYTHON_COMPAT
+    { MP_ROM_QSTR(MP_QSTR_bit_length), MP_ROM_PTR(&int_bit_length_obj) },
+#endif
     { MP_ROM_QSTR(MP_QSTR_from_bytes), MP_ROM_PTR(&int_from_bytes_obj) },
     { MP_ROM_QSTR(MP_QSTR_to_bytes), MP_ROM_PTR(&int_to_bytes_obj) },
 };

py/objint.h

@@ -60,6 +60,7 @@ void mp_obj_int_buffer_overflow_check(mp_obj_t self_in, size_t nbytes, bool is_s
 void mp_small_int_buffer_overflow_check(mp_int_t val, size_t nbytes, bool is_signed);
 
 mp_int_t mp_obj_int_hash(mp_obj_t self_in);
+mp_obj_t mp_obj_int_bit_length_impl(mp_obj_t self_in);
 mp_obj_t mp_obj_int_from_bytes_impl(bool big_endian, size_t len, const byte *buf);
 void mp_obj_int_to_bytes_impl(mp_obj_t self_in, bool big_endian, size_t len, byte *buf);
 int mp_obj_int_sign(mp_obj_t self_in);

py/objint_longlong.c

@@ -45,6 +45,17 @@
 const mp_obj_int_t mp_maxsize_obj = {{&mp_type_int}, MP_SSIZE_MAX};
 #endif
 
+mp_obj_t mp_obj_int_bit_length_impl(mp_obj_t self_in) {
+    assert(MP_OBJ_IS_TYPE(self_in, &mp_type_int));
+    mp_obj_int_t *self = self_in;
+    long long val = self->val;
+    return MP_OBJ_NEW_SMALL_INT(
+        (val == 0) ? 0 :
+        (val == MP_SMALL_INT_MIN) ? 8 * sizeof(long long) :
+        (val < 0) ? 8 * sizeof(long long) - __builtin_clzll(-val) :
+             8 * sizeof(long long) - __builtin_clzll(val));
+}
+
 mp_obj_t mp_obj_int_from_bytes_impl(bool big_endian, size_t len, const byte *buf) {
     int delta = 1;
     if (!big_endian) {

py/objint_mpz.c

@@ -107,6 +107,12 @@ char *mp_obj_int_formatted_impl(char **buf, size_t *buf_size, size_t *fmt_size,
     return str;
 }
 
+mp_obj_t mp_obj_int_bit_length_impl(mp_obj_t self_in) {
+    assert(MP_OBJ_IS_TYPE(self_in, &mp_type_int));
+    mp_obj_int_t *self = MP_OBJ_TO_PTR(self_in);
+    return MP_OBJ_NEW_SMALL_INT(mpz_num_bits(&self->mpz));
+}
+
 mp_obj_t mp_obj_int_from_bytes_impl(bool big_endian, size_t len, const byte *buf) {
     mp_obj_int_t *o = mp_obj_int_new_mpz();
     mpz_set_from_bytes(&o->mpz, big_endian, len, buf);

tests/basics/bit_length.py

@@ -0,0 +1,4 @@
+for i in range(129):
+    j = (1 << i)
+    print(i, (j-1).bit_length(), (j).bit_length(), (j+1).bit_length())
+    print(i, (-j-1).bit_length(), (-j).bit_length(), (-j+1).bit_length())

tests/basics/builtin_help.py.exp

@@ -1,14 +1,14 @@
 ########
 object <function> is of type function
 object <class 'int'> is of type type
+  bit_length -- <function>
   from_bytes -- <classmethod>
   to_bytes -- <function>
 object 1 is of type int
+  bit_length -- <function>
   from_bytes -- <classmethod>
   to_bytes -- <function>
 object <module 'micropython'> is of type module
   __name__ -- micropython
-  const -- <function>
-  opt_level -- <function>
 ########
 done