[Decompilation] KAJA driver ISR magic check

Down to one inline ASM instruction for these. Part of P0139, funded by [Anonymous].
nmlgc · May 11, 2021 · acd2985 · acd2985
1 parent 8e16481
commit acd2985
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Showing 5 changed files with 31 additions and 27 deletions.
diff --git a/libs/kaja/kaja.h b/libs/kaja/kaja.h
@@ -23,6 +23,19 @@ typedef enum {
 #define PMD 0x60
 #define MMD 0x61
 
+// Memory structure of a KAJA interrupt service routine, pointed to by its
+// address stored in the x86 interrupt vector. Used for identifying whether
+// PMD or MMD are installed at a certain IRQ#, by checking [magic].
+typedef struct {
+	uint8_t jmp[2];  	// JMP to the code
+	uint8_t magic[3];	// "PMD" or "MMD"
+} kaja_isr_t;
+
+#define kaja_isr_magic_matches(isr, magic1, magic2, magic3) \
+	(((kaja_isr_t *)(isr))->magic[0] == magic1) && \
+	(((kaja_isr_t *)(isr))->magic[1] == magic2) && \
+	(((kaja_isr_t *)(isr))->magic[2] == magic3)
+
 // MMDFUNC.DOC and https://gist.github.com/devinacker/bdc58cfdba6a1ee80449
 // both imply that this is a hardcoded property of the MMD format
 #define MMD_TICKS_PER_QUARTER_NOTE 48

diff --git a/th02/op_01.cpp b/th02/op_01.cpp
@@ -5,11 +5,11 @@
 
 extern "C" {
 #include <process.h>
-#include "libs/kaja/kaja.h"
 #include "th02/th02.h"
 #include "x86real.h"
 #include "th02/resident.hpp"
 #include "master.hpp"
+#include "libs/kaja/kaja.h"
 #include "th02/hardware/frmdelay.h"
 #include "th02/hardware/grp_rect.h"
 #include "th02/hardware/input.hpp"

diff --git a/th02/op_06.cpp b/th02/op_06.cpp
@@ -4,10 +4,10 @@
  */
 
 extern "C" {
-#include "libs/kaja/kaja.h"
 #include "th02/th02.h"
 #include "x86real.h"
 #include "master.hpp"
+#include "libs/kaja/kaja.h"
 #include "th01/math/polar.hpp"
 #include "th02/math/vector.hpp"
 #include "th02/hardware/frmdelay.h"

diff --git a/th02/snd/mmd_res.c b/th02/snd/mmd_res.c
@@ -1,27 +1,23 @@
 #pragma option -WX -zCSHARED -k-
 
 #include "platform.h"
+#include "x86real.h"
 #include "libs/kaja/kaja.h"
 #include "th02/snd/snd.h"
 
 bool16 snd_mmd_resident(void)
 {
 	_ES = 0;
-	__asm	les bx, dword ptr es:[MMD * 4];
-	__asm	cmp byte ptr es:[bx+2], 'M';
-	__asm	jnz nope;
-	__asm	cmp byte ptr es:[bx+3], 'M';
-	__asm	jnz nope;
-	__asm	cmp byte ptr es:[bx+4], 'D';
-	__asm	jnz nope;
-	snd_interrupt_if_midi = MMD;
-	snd_midi_active = true;
-	snd_midi_possible = true;
-	// Enforced by the -WX code generation. Just replace these two lines with
-	// `return true`.
-	_AX = true;
-	__asm	retf;
-nope:
+	__asm { les bx, dword ptr es:[MMD * 4]; }
+	if(kaja_isr_magic_matches(MK_FP(_ES, _BX), 'M', 'M', 'D')) {
+		snd_interrupt_if_midi = MMD;
+		snd_midi_active = true;
+		snd_midi_possible = true;
+		// Enforced by the -WX code generation. Just replace these two lines
+		// with `return true`.
+		_AX = true;
+		__asm	retf;
+	}
 	snd_midi_possible = false;
 	return false;
 }

diff --git a/th02/snd/pmd_res.c b/th02/snd/pmd_res.c
@@ -1,6 +1,7 @@
 #pragma option -zCSHARED -k-
 
 #include "platform.h"
+#include "x86real.h"
 #include "libs/kaja/kaja.h"
 #include "th02/snd/snd.h"
 
@@ -12,16 +13,10 @@ bool16 snd_pmd_resident(void)
 	snd_midi_possible = false;
 
 	_ES = 0;
-	__asm	les bx, dword ptr es:[PMD * 4];
-	__asm	cmp byte ptr es:[bx+2], 'P';
-	__asm	jnz nope;
-	__asm	cmp byte ptr es:[bx+3], 'M';
-	__asm	jnz nope;
-	__asm	cmp byte ptr es:[bx+4], 'D';
-	__asm	jnz nope;
-	return true;
-nope:
+	__asm { les bx, dword ptr es:[PMD * 4] };
+	if(kaja_isr_magic_matches(MK_FP(_ES, _BX), 'P', 'M', 'D')) {
+		return true;
+	}
 	return false;
 }
-
 #pragma codestring "\x90"