py/objint: Simplify mp_int_format_size and remove unreachable code.

One never needs to format integers with a base larger than 16 (but code
can be easily extended beyond this value if needed in the future).

py/objint.c

@@ -151,23 +151,21 @@ typedef mp_int_t fmt_int_t;
 #endif
 
 STATIC const uint8_t log_base2_floor[] = {
-    0,
     0, 1, 1, 2,
     2, 2, 2, 3,
     3, 3, 3, 3,
     3, 3, 3, 4,
+    /* if needed, these are the values for higher bases
     4, 4, 4, 4,
     4, 4, 4, 4,
     4, 4, 4, 4,
     4, 4, 4, 5
+    */
 };
 
 size_t mp_int_format_size(size_t num_bits, int base, const char *prefix, char comma) {
-    if (base < 2 || base > 32) {
-        return 0;
-    }
-
-    size_t num_digits = num_bits / log_base2_floor[base] + 1;
+    assert(2 <= base && base <= 16);
+    size_t num_digits = num_bits / log_base2_floor[base - 1] + 1;
     size_t num_commas = comma ? num_digits / 3 : 0;
     size_t prefix_len = prefix ? strlen(prefix) : 0;
     return num_digits + num_commas + prefix_len + 2; // +1 for sign, +1 for null byte