From fbedf7cf6745178167a8434335b590764740fe72 Mon Sep 17 00:00:00 2001
From: Joseph Ferano <joseph@ferano.io>
Date: Fri, 14 Feb 2025 23:08:45 +0700
Subject: [PATCH] Process mov instruction properly, 01-02-39.asm now decoded
 properly

---
 decoder8086.odin | 125 ++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 97 insertions(+), 28 deletions(-)

diff --git a/decoder8086.odin b/decoder8086.odin
index 2aaaeac..0c64264 100644
--- a/decoder8086.odin
+++ b/decoder8086.odin
@@ -51,6 +51,34 @@ instructions := [?]Instruction {
 }
 
 inst_map := make(map[u8]Instruction)
+RIGHT_ALIGN_AMOUNT := 30
+
+get_instruction :: proc(bytes: []u8) -> (Instruction, u8) {
+    return {}, 0
+}
+
+calculate_effective_address :: proc(r_m: u8) -> string {
+    val: string
+    switch r_m {
+    case 0b000:
+        val = "bx + si"
+    case 0b001:
+        val = "bx + di"
+    case 0b010:
+        val = "bp + si"
+    case 0b011:
+        val = "bp + di"
+    case 0b100:
+        val = "si"
+    case 0b101:
+        val = "di"
+    case 0b110:
+        val = "bp"
+    case 0b111:
+        val = "bx"
+    }
+    return val
+}
 
 main :: proc() {
     ax := registers[0]
@@ -72,48 +100,89 @@ main :: proc() {
         inst_map[inst.encoding] = inst
     }
 
-    if true {
+    if false {
         for i in 0..<bytes_read {
-            fmt.printfln("%b", data[i])
-            mask: u8 = 0b11111111
-            for i in 0..=4 {
+            fmt.printfln("Checking %b:", data[i])
+            mask: u8 = 0xFF
+            for j in 0..=4 {
                 encoding := data[i] & mask
+                fmt.printfln("\tNext: %b %b", data[i], encoding)
                 if inst, ok := inst_map[encoding]; ok {
-                    fmt.printfln("%b, %v", encoding, inst.desc)
-                    // fmt.println(inst.desc)
+                    fmt.printfln("\t%b, %v", encoding, inst.desc)
                     break
                 }
                 mask <<= 1
             }
-            // fmt.println("=============")
         }
         os.exit(0)
     }
 
     read_next := false
     src_dst := true
-    is_word := false
-    prev :u8 = 0
     fmt.println("bits 16\n")
-    for i in 0..<bytes_read {
-        b := data[i]
-        if read_next {
-            mod := (b & 0b11000000) >> 6
-            reg := (b & 0b00111000) >> 3
-            rm  := b & 0b00000111
-            src_name := is_word ? registers[reg].fullname : registers[reg].bytename
-            dst_name := is_word ? registers[rm].fullname : registers[rm].bytename
-            fmt.printfln("mov %s, %s     ;; %b  %b", dst_name, src_name, prev, b)
-            read_next = false
-            continue
+    processed := 0
+    for processed < bytes_read {
+        curr_byte := data[processed]
+        if curr_byte & 0b11111000 == 0b10001000 {
+            is_word := curr_byte & 1 == 1
+            flip_src := curr_byte & 2 != 0
+            disp_amount := 0
+
+            next_byte := data[processed + 1]
+            mod := (next_byte & 0b11000000) >> 6
+            reg := (next_byte & 0b00111000) >> 3
+            rm  := next_byte & 0b00000111
+            dst_reg := registers[rm]
+
+            disp: string
+            if mod == 1 {
+                disp_byte := (i16)(data[processed + 2])
+                disp_amount = 1
+                disp = disp_byte == 0 ? "" : fmt.aprintf(" + %d", disp_byte)
+            } else if mod == 2 {
+                disp_byte := (i16)(data[processed + 3]) << 8 | (i16)(data[processed + 2])
+                disp_amount = 2
+                disp = disp_byte == 0 ? "" : fmt.aprintf(" + %d", disp_byte)
+            } else {
+                disp = ""
+            }
+            src_name: string
+            if mod == 3 {
+                // Register-to-register
+                src_name = is_word ? registers[rm].fullname : registers[rm].bytename
+            } else {
+                src_name = fmt.aprintf("[%s%s]", calculate_effective_address(rm), disp)
+            }
+
+            dst_name := is_word ? registers[reg].fullname : registers[reg].bytename
+
+            if flip_src { src_name, dst_name = dst_name, src_name }
+
+            processed += 1 + ((int)(mod) % 3)
+
+            inst_string := fmt.aprintf("mov %s, %s", src_name, dst_name)
+
+            fmt.printfln("%s %*[1]s %08b  %08b", inst_string, RIGHT_ALIGN_AMOUNT - len(inst_string), ";; 1", curr_byte, next_byte)
+        } else if curr_byte & 0b1111_0000 == 0b10110000 {
+            is_word := curr_byte & 0b0000_1000 != 0
+            reg := curr_byte & 0b00000111
+            dst_name: string
+            imm: i16
+            if is_word {
+                dst_name = registers[reg].fullname
+                imm = (i16)(data[processed+2]) << 8 | (i16)(data[processed+1])
+                processed += 2
+            } else {
+                dst_name = registers[reg].bytename
+                imm = (i16)(data[processed+1])
+                processed += 1
+            }
+            inst_string := fmt.aprintf("mov %s, %d", dst_name, imm)
+            fmt.printfln("%s %*[1]s %08b  %08b", inst_string, RIGHT_ALIGN_AMOUNT - len(inst_string), ";; 2", curr_byte, data[processed + 1])
+
+        } else {
+            fmt.printfln("unknown instruction ;; %b", curr_byte)
         }
-        if b == 0b10001001 {
-            read_next = true
-            is_word = true
-        } else if b == 0b10001000 {
-            read_next = true
-            is_word = false
-        }
-        prev = b
+        processed += 1
     }
 }