py/modbuiltins: Add support for rounding integers.

As per CPython semantics.  This feature is controlled by
MICROPY_PY_BUILTINS_ROUND_INT which is disabled by default.

1 files changed, 30 insertions, 1 deletions

diff --git a/py/modbuiltins.c b/py/modbuiltins.c
index 0d511338b..b216e021f 100644
--- a/py/modbuiltins.c
+++ b/py/modbuiltins.c
@@ -445,7 +445,36 @@ MP_DEFINE_CONST_FUN_OBJ_1(mp_builtin_repr_obj, mp_builtin_repr);
 STATIC mp_obj_t mp_builtin_round(size_t n_args, const mp_obj_t *args) {
     mp_obj_t o_in = args[0];
     if (MP_OBJ_IS_INT(o_in)) {
-        return o_in;
+        if (n_args <= 1) {
+            return o_in;
+        }
+
+        #if !MICROPY_PY_BUILTINS_ROUND_INT
+        mp_raise_NotImplementedError(NULL);
+        #else
+        mp_int_t num_dig = mp_obj_get_int(args[1]);
+        if (num_dig >= 0) {
+            return o_in;
+        }
+
+        mp_obj_t mult = mp_binary_op(MP_BINARY_OP_POWER, MP_OBJ_NEW_SMALL_INT(10), MP_OBJ_NEW_SMALL_INT(-num_dig));
+        mp_obj_t half_mult =  mp_binary_op(MP_BINARY_OP_FLOOR_DIVIDE, mult, MP_OBJ_NEW_SMALL_INT(2));
+        mp_obj_t modulo = mp_binary_op(MP_BINARY_OP_MODULO, o_in, mult);
+        mp_obj_t rounded = mp_binary_op(MP_BINARY_OP_SUBTRACT, o_in, modulo);
+        if (mp_obj_is_true(mp_binary_op(MP_BINARY_OP_MORE, half_mult, modulo))) {
+            return rounded;
+        } else if (mp_obj_is_true(mp_binary_op(MP_BINARY_OP_MORE, modulo, half_mult))) {
+            return mp_binary_op(MP_BINARY_OP_ADD, rounded, mult);
+        } else {
+            // round to even number
+            mp_obj_t floor = mp_binary_op(MP_BINARY_OP_FLOOR_DIVIDE, o_in, mult);
+            if (mp_obj_is_true(mp_binary_op(MP_BINARY_OP_AND, floor, MP_OBJ_NEW_SMALL_INT(1)))) {
+                return mp_binary_op(MP_BINARY_OP_ADD, rounded, mult);
+            } else {
+                return rounded;
+            }
+        }
+        #endif
     }
 #if MICROPY_PY_BUILTINS_FLOAT
     mp_float_t val = mp_obj_get_float(o_in);