[Reverse-engineering] [th02/th03/th04/th05] snd_load() buffer size

Hardcoding these *might* have been acceptable if the numbers actually
matched the sizes defined in GAME.BAT, but they don't. With PMD's
AH=22h function, there's really no excuse though.
About time I looked into this, and expressed that constant as an inline
function that can easily be replaced with a proper implementation.

Part of P0139, funded by [Anonymous].

libs/kaja/kaja.h

@@ -24,6 +24,11 @@ typedef enum {
 	PMD_SE_PLAY = 0x0C,
 	PMD_GET_WORKAREA_ADDRESS = 0x10,
 
+	// Returns the sizes of the song (AL), instrument (AH), and sound effect
+	// (DL) buffers, in KiB. These can be customized on the PMD command line
+	// with the /M, /V and /E options respectively.
+	PMD_GET_BUFFER_SIZES = 0x22,
+
 	_kaja_func_t_FORCE_UINT16 = 0xFFFF
 } kaja_func_t;
 

th02/snd/load.cpp

@@ -1,5 +1,6 @@
 #pragma option -zCSHARED
 
+extern "C" {
 #include "platform.h"
 #include "x86real.h"
 #include "libs/kaja/kaja.h"
@@ -47,7 +48,7 @@ void snd_load(const char fn[SND_FN_LEN], kaja_func_t func)
 
 	// DOS file read; song data address is in DS:DX
 	_AX = 0x3F00;
-	_CX = 0x5000;
+	_CX = snd_load_size();
 	geninterrupt(0x21);
 
 	__asm { pop ds; }
@@ -56,3 +57,5 @@ void snd_load(const char fn[SND_FN_LEN], kaja_func_t func)
 	_AH = 0x3E;
 	geninterrupt(0x21);
 }
+
+}

th02/snd/snd.h

@@ -60,6 +60,19 @@ void snd_delay_until_volume(uint8_t volume);
 #define SND_FN_LEN 13
 
 #if defined(PMD) && (GAME <= 3) /* requires kaja.h */
+	#if defined(__cplusplus) && (GAME <= 4)
+		static inline uint16_t snd_load_size() {
+			// ZUN bug: Should rather retrieve the maximum data size for song
+			// or sound effect data via PMD_GET_BUFFER_SIZES, instead of
+			// hardcoding a random maximum and risking overflowing PMD's data
+			// buffer.
+			// (Unfortunately, MMD lacks a similar function...)
+			// MODDERS: When implementing this properly, rearrange the call
+			// sites to make sure that AX isn't destroyed.
+			return 0x5000;
+		}
+	#endif
+
 	// Loads a song in .M format ([func] = SND_LOAD_SONG) or a sound effect
 	// bank in EFC format ([func] = SND_LOAD_SE) into the respective work
 	// buffer of the sound driver. If MIDI is used, 'md' is appended to the

th02/snd_load.c

@@ -1 +0,0 @@
-#include "th02/snd/load.c"

th02/snd_load.cpp

@@ -0,0 +1 @@
+#include "th02/snd/load.cpp"

th04/snd/snd.h

@@ -39,6 +39,7 @@ static inline bool16 snd_se_active() {
 // sets [snd_se_mode] and [snd_bgm_mode] accordingly. Returns [snd_bgm_mode].
 int pascal snd_determine_modes(int req_bgm_mode, int req_se_mode);
 
+#if defined(PMD) /* requires kaja.h */
 // Loads a song ([func] = SND_LOAD_SONG) or a sound effect bank ([func] =
 // SND_LOAD_SE) into the respective work buffer of the sound driver. [fn] must
 // not have any extension. Depending on [snd_bgm_mode], [snd_se_mode], and
@@ -60,3 +61,11 @@ int pascal snd_determine_modes(int req_bgm_mode, int req_se_mode);
 // Note that the TH05 version will infinitely loop if neither the file for the
 // current [snd_bgm_mode] nor "[fn].m" exist.
 void pascal snd_load(const char fn[SND_FN_LEN], int16_t func);
+
+#if defined(__cplusplus) && (GAME == 5)
+	// Refer to TH02's implementation for an explanation of how wrong this is.
+	static inline uint16_t snd_load_size() {
+		return 0xFFFF;
+	}
+#endif
+#endif

th05/snd/load.cpp

@@ -101,7 +101,7 @@ void pascal snd_load(const char fn[SND_FN_LEN], int16_t func)
 
 	// DOS file read; song data address is in DS:DX
 	_AX = 0x3F00;
-	_CX = 0xFFFF;
+	_CX = snd_load_size();
 	geninterrupt(0x21);
 
 	// DOS file close