[Decompilation] [th03] Add a type for the paletted playchar IDs

Much better than the previous incorrect comment, since the char_id()
method now easily generates the correct sequence of conversion
instructions, seen all throughout the ASM. Even within array
subscripts!

Part of P0076, funded by [Anonymous] and -Tom-.

Research/Borland C++ decompilation.md

@@ -39,6 +39,7 @@ where the scalar-type variable is declared in relation to them.
 |-|-|
 | `ADD [m8], imm8` | Only achievable through a C++ method operating on a  member? |
 | `MOV AL, [m8]`<br />`ADD AL, imm8`<br />`MOV [m8], AL` | Opposite; *not* an inlined function |
+| `CWD`<br />`SUB AX, DX`<br />`SAR AX, 1` | `AX / 2`, `AX` is *int* |
 
 ### Arithmetic on a register *after* assigning it to a variable?
 

th03/chars/chars.hpp

@@ -11,6 +11,23 @@ typedef enum {
 	PLAYCHAR_COUNT = 9,
 } playchars_t;
 
+// Encodes a playchars_t together with its alternate palette flag.
+#pragma option -a1
+struct playchar_paletted_t {
+	unsigned char v;
+
+	int filename_id() const {
+		return (v - 1);
+	}
+
+	playchars_t char_id() const {
+		return static_cast<playchars_t>(filename_id() / 2);
+	}
+};
+#pragma option -a.
+
+#define TO_PALETTED(playchar) ((playchar << 1) + 1)
+
 typedef struct {
 	SPPoint8 aligned;
 	SPPoint8 diagonal;

th03/player/player.hpp

@@ -37,10 +37,7 @@ typedef struct {
 	uint8_t unused_1;
 	unsigned char invincibility_time;
 	char halfhearts;
-
-	// (<value from playchars_t> + 1) << 1 | <alternative palette flag>
-	unsigned char playchar_paletted;
-
+	playchar_paletted_t playchar_paletted;
 	speed_t speed;
 	shot_mode_t shot_mode;
 	unsigned char patnum_movement;