parsenum: Signedness issues.

char can be signedness, and using signedness types is dangerous - it can
lead to negative offsets when doing table lookups. We apparently should just
ban char usage.

py/parsenum.c

@@ -40,8 +40,9 @@
 #include <math.h>
 #endif
 
-mp_obj_t mp_parse_num_integer(const char *restrict str, uint len, int base) {
-    const char *restrict top = str + len;
+mp_obj_t mp_parse_num_integer(const char *restrict str_, uint len, int base) {
+    const byte *restrict str = (const byte *)str_;
+    const byte *restrict top = str + len;
     bool neg = false;
     mp_obj_t ret_val;
 
@@ -65,11 +66,11 @@ mp_obj_t mp_parse_num_integer(const char *restrict str, uint len, int base) {
     }
 
     // parse optional base prefix
-    str += mp_parse_num_base(str, top - str, &base);
+    str += mp_parse_num_base((const char*)str, top - str, &base);
 
     // string should be an integer number
     machine_int_t int_val = 0;
-    const char *restrict str_val_start = str;
+    const byte *restrict str_val_start = str;
     for (; str < top; str++) {
         // get next digit as a value
         int dig = *str;
@@ -129,9 +130,9 @@ have_ret_val:
 overflow:
     // reparse using long int
     {
-        const char *s2 = str_val_start;
+        const char *s2 = (const char*)str_val_start;
         ret_val = mp_obj_new_int_from_str_len(&s2, top - str_val_start, neg, base);
-        str = s2;
+        str = (const byte*)s2;
         goto have_ret_val;
     }
 

py/parsenumbase.c

@@ -31,7 +31,7 @@
 // find real radix base, and strip preceding '0x', '0o' and '0b'
 // puts base in *base, and returns number of bytes to skip the prefix
 int mp_parse_num_base(const char *str, uint len, int *base) {
-    const char *p = str;
+    const byte *p = (const byte*)str;
     int c = *(p++);
     if ((*base == 0 || *base == 16) && c == '0') {
         c = *(p++);
@@ -63,6 +63,6 @@ int mp_parse_num_base(const char *str, uint len, int *base) {
         }
         p--;
     }
-    return p - str;
+    return p - (const byte*)str;
 }