From 95ad808ef8ea804ed778719606781ba35bfe7a6f Mon Sep 17 00:00:00 2001
From: Bad Diode <bd@badd10de.dev>
Date: Mon, 28 Aug 2023 12:15:25 +0200
Subject: Add multiply instructions

---
 src/main.c     | 60 ++++++++++++++++++----------------------------------------
 src/uxn-core.s | 17 +++++++++++++++++
 2 files changed, 35 insertions(+), 42 deletions(-)

diff --git a/src/main.c b/src/main.c
index 4a4b58c..315292e 100644
--- a/src/main.c
+++ b/src/main.c
@@ -26,8 +26,6 @@
 #include "profiling.c"
 #include "devices.c"
 
-#define STACK_SIZE 16
-u8 stack[STACK_SIZE] = {0};
 extern void uxn_eval_asm(u16 pc);
 
 // TODO: This should be on the IWRAM for maximum speed, as these are operations
@@ -39,7 +37,7 @@ extern uintptr_t wst_ptr;
 extern uintptr_t rst_ptr;
 
 EWRAM_BSS
-u8 uxn_ram[KB(64) * 2];
+u8 uxn_ram[KB(64)];
 
 void
 init_uxn() {
@@ -49,39 +47,18 @@ init_uxn() {
     // uxn_boot(u, uxn_ram, uxn_dei, uxn_deo);
 
     // Copy rom to VM.
-    u8 uxn_rom[32] = {
-        // Hello world (h)
-        // 0x80, 0x68, 0x80, 0x18, 0x17,
+    u8 uxn_rom[] = {
         //
-        // ADD test
-        // 0x80, 0x04, 0x80, 0x03, 0x80, 0x02, 0x80, 0x01, 0x18, 0x18
-        // SUB test
-        // 0x80, 0x04, 0x80, 0x03, 0x80, 0x02, 0x80, 0x01, 0x19, 0x19, 0x19
-        // LIT2 04 03 LIT2 02 01 ADD ADD ADD BRK
-        // 0xa0, 0x04, 0x03,
-        // 0xa0, 0x04, 0x03, 0xa0, 0x02, 0x01,
-        // 0xa0, 0x04, 0x03, 0xa0, 0x02, 0x01, 0x18, 0x18, 0x00
-        // #0004 #0008 ADD
-        // 0xa0, 0x00, 0x04, 0xa0, 0x00, 0x08, 0x18,
-        // #0004 #0008 ADD2
-        // 0x80, 0xFF, 0xff,
-        // 0xa0, 0x00, 0x08, 0xa0, 0x00, 0x04, 0x38,
-        // 0xa0, 0x00, 0x08, 0xa0, 0x00, 0x04, 0x38,
-        // 0xa0, 0x00, 0x08, 0xa0, 0x00, 0x03, 0x39,
-        // 0xa0, 0x00, 0x01, 0x38,
-        //
-        // 0x80, 0xFF, 0xff,
-        // 0xa0, 0xba, 0xdd,
-        // 0xa0, 0x10, 0xde,
-        // 0xa0, 0xfe, 0xed,
-        // 0xa0, 0xde, 0xaf,
-        // 0xa0, 0xba, 0xdd,
-        // 0xa0, 0x10, 0xde,
-        // 0xa0, 0xfe, 0xed,
-        // 0xa0, 0xde, 0xaf,
-        //
-        // #0008 #0003 SUB2
-        // 0xa0, 0x00, 0x08, 0xa0, 0x00, 0x03,
+        // ADD test.
+        0x80, 0x04, 0x80, 0x08, 0x18,             // #04 #08 ADD      -> 0c
+        0xa0, 0x00, 0x04, 0xa0, 0x00, 0x08, 0x38, // #0004 #0008 ADD2 -> 000c
+        // SUB test.
+        0x80, 0x08, 0x80, 0x03, 0x19,             // #08 #03 ADD      -> 05
+        0xa0, 0x00, 0x08, 0xa0, 0x00, 0x03, 0x39, // #0008 #0003 ADD2 -> 0005
+        // MUL test.
+        0x80, 0x03, 0x80, 0x04, 0x1a,             // #03 #04 MUL      -> 0c
+        0xa0, 0x00, 0x03, 0xa0, 0x00, 0x04, 0x3a, // #0003 #0004 MUL2 -> 000c
+        0xa0, 0x00, 0xff, 0xa0, 0x00, 0x02, 0x3a, // #00ff #0002 MUL2 -> 01fe
     };
     memcpy(uxn_ram + PAGE_PROGRAM, uxn_rom, sizeof(uxn_rom));
 }
@@ -127,8 +104,8 @@ main(void) {
         io_ports[i] = 0;
     }
 
-    txt_printf("ROM\n\n");
-    for (size_t i = 0; i < 32; i++) {
+    txt_printf("ROM");
+    for (size_t i = 0; i < 64; i++) {
         if (i % 8 == 0) {
             txt_printf("\n");
         }
@@ -137,17 +114,16 @@ main(void) {
     txt_printf("\n\n");
 
     uxn_eval_asm(PAGE_PROGRAM);
-    txt_printf("STACK\n");
-    txt_printf("PTR: %d\n", wst_ptr - (uintptr_t)wst);
-    for (size_t i = 0; i < STACK_SIZE; i++) {
+    txt_printf("STACK (");
+    txt_printf("PTR: %d)", wst_ptr - (uintptr_t)wst);
+    for (size_t i = 0; i < 64; i++) {
         if (i % 8 == 0) {
             txt_printf("\n");
         }
         txt_printf("%02x ", wst[i]);
     }
 
-    uintptr_t stack_base = wst;
-    uintptr_t stack_size = wst_ptr - stack_base;
+    uintptr_t stack_size = wst_ptr - (uintptr_t)wst;
     while(true) {
         txt_position(0,0);
         // bios_vblank_wait();
diff --git a/src/uxn-core.s b/src/uxn-core.s
index 32ec26b..e35707f 100644
--- a/src/uxn-core.s
+++ b/src/uxn-core.s
@@ -257,15 +257,32 @@ sub2:
     b       uxn_decode
 
 mul:
+    ldr     r3, [r1, #-1]!
+    ldr     r4, [r1, #-1]!
+    mul     r4, r3, r4
+    strb    r4, [r1], #1
     b       uxn_decode
 
 mul2:
+    ldrb    r3, [r1, #-1]!
+    ldrb    r5, [r1, #-1]!
+    orr     r3, r5, r3, lsl #8
+    ldrb    r4, [r1, #-1]!
+    ldrb    r5, [r1, #-1]!
+    orr     r4, r5, r4, lsl #8
+    mul     r5, r3, r4
+    lsr     r3, r5, #24
+    strb    r3, [r1], #1
+    lsr     r5, #16
+    strb    r5, [r1], #1
     b       uxn_decode
 
 div:
+@ TODO: Implement using ____aeabi_uidiv_from_thumb
     b       uxn_decode
 
 div2:
+@ TODO: Implement using ____aeabi_uidiv_from_thumb
     b       uxn_decode
 
 and:
-- 
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