listing: encapsulate the list_options encoding, make more comprehensive

Encapsulate the list_options() encoding in an inline function. We only
ever compute a mask with a non-constant input in two places (command
line and pragma parsing), so a slightly more complex mapping is of no
consequence; thus map a-z, A-Z and 0-9 as being the most likely
characters we may want to use as options. Space is left for two more :)

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

asm/listing.c

@@ -412,10 +412,7 @@ static void list_update_options(const char *str)
             state = false;
             break;
         default:
-            c -= '@';
-            if (c > 63)
-                break;
-            mask = UINT64_C(1) << c;
+            mask = list_option_mask(c);
             if (state)
                 list_options |= mask;
             else

asm/listing.h

@@ -125,19 +125,44 @@ extern bool user_nolist;
  */
 extern uint64_t list_options, active_list_options;
 
-static inline bool list_option(char x)
+/*
+ * This maps the characters a-z, A-Z and 0-9 onto a 64-bit bitmask
+ * (with two bits left over for future use! This isn't particularly
+ * efficient code, but just about every instance of it should be
+ * fed a constant, so the entire function can be precomputed at
+ * compile time.
+ *
+ * This returns 0 for invalid values, so that no bit is accessed
+ * for unsupported characters.
+ */
+static inline const_func uint64_t list_option_mask(unsigned char x)
 {
-    unsigned int p = x - '@';
-    if (p > 63)
-        return false;
-    return unlikely(active_list_options & (UINT64_C(1) << p));
+    if (x >= 'a') {
+        if (x > 'z')
+            return 0;
+        x = x - 'a';
+    } else if (x >= 'A') {
+        if (x > 'Z')
+            return 0;
+        x = x - 'A' + 26;
+    } else if (x >= '0') {
+        if (x > '9')
+            return 0;
+        x = x - '0' + 26*2;
+    }
+
+    return UINT64_C(1) << x;
+}
+
+static inline pure_func bool list_option(unsigned char x)
+{
+    return unlikely(active_list_options & list_option_mask(x));
 }
 
 /* We can't test this using active_list_options for obvious reasons... */
-static inline bool list_on_every_pass(void)
+static inline pure_func bool list_on_every_pass(void)
 {
-    const unsigned int p = 'p' - '@';
-    return unlikely(list_options & (UINT64_C(1) << p));
+    return unlikely(list_options & list_option_mask('p'));
 }
 
 /* Pragma handler */

asm/nasm.c

@@ -1011,12 +1011,8 @@ static bool process_arg(char *p, char *q, int pass)
 
         case 'L':        /* listing options */
             if (pass == 2) {
-                while (*param) {
-                    unsigned int p = *param - '@';
-                    if (p <= 63)
-                        list_options |= (UINT64_C(1) << p);
-                    param++;
-                }
+                while (*param)
+                    list_options |= list_option_mask(*param++);
             }
             break;