From 8e4f7419a18da66826f7c88cd1497b627a7efd9f Mon Sep 17 00:00:00 2001
From: Rokas Puzonas <rokas.puz@gmail.com>
Date: Sun, 9 Apr 2023 20:46:23 +0300
Subject: [PATCH] complete homework 2

---
 src/asm.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 52 insertions(+), 9 deletions(-)

diff --git a/src/asm.c b/src/asm.c
index fd9bf32..38bb483 100644
--- a/src/asm.c
+++ b/src/asm.c
@@ -1,15 +1,31 @@
 #include <inttypes.h>
 #include <stdio.h>
 #include <stdbool.h>
+#include <assert.h>
 
 #define u32 uint32_t
 #define u16 uint16_t
 #define u8  uint8_t
 
+#define todo(...) fprintf(stderr, "TODO(%s:%d): ", __FILE__, __LINE__); fprintf(stderr, __VA_ARGS__); abort()
+#define dbg(...) printf("; "); printf(__VA_ARGS__); printf("\n")
+
 const char *wide_reg_names[8]     = { "ax", "cx", "dx", "bx", "sp", "bp", "si", "di" };
 const char *non_wide_reg_names[8] = { "al", "cl", "dl", "bl", "ah", "ch", "dh", "bh" };
 
+const char *mod_lookup_names[8] = {
+    "bx + si",
+    "bx + di",
+    "bp + si",
+    "bp + di",
+    "si",
+    "di",
+    "bp",
+    "bx"
+};
+
 const char *lookup_reg_name(u8 idx, bool wide) {
+    assert(0 <= idx && idx <= 7);
     if (wide) {
         return wide_reg_names[idx];
     } else {
@@ -19,30 +35,57 @@ const char *lookup_reg_name(u8 idx, bool wide) {
 
 void dissassemble(FILE *src, FILE *dst) {
     fprintf(dst, "bits 16\n\n");
-    while (!feof(src)) {
+    while (true) {
         u8 byte1 = fgetc(src);
-        u8 byte2 = fgetc(src);
+        if (feof(src)) break;
 
         // Register memory to/from register
         if ((byte1 & 0b11111100) == 0b10001000) {
+            u8 byte2 = fgetc(src);
             bool wide = byte1 & 0b1;
             bool direction = (byte1 & 0b10) >> 1;
 
             u8 mod =  byte2 & 0b11000000;
             u8 reg = (byte2 & 0b00111000) >> 3;
             u8 rm  =  byte2 & 0b00000111;
+            const char *reg_name = lookup_reg_name(reg, wide);
+            char rm_name[24] = { 0 };
             if (mod == 0b11000000) { // Mod = 0b11
-                const char *reg_name = lookup_reg_name(reg, wide);
-                const char *rm_name  = lookup_reg_name(rm, wide);
-                if (direction) {
-                    fprintf(dst, "mov %s, %s\n", reg_name, rm_name);
-                } else {
-                    fprintf(dst, "mov %s, %s\n", rm_name, reg_name);
-                }
+                strcpy(rm_name, lookup_reg_name(rm, wide));
             } else if (mod == 0b10000000) { // Mod = 0b10
+                u16 immidiate = fgetc(src) | (fgetc(src) << 8);
+                snprintf(rm_name, sizeof(rm_name), "[%s + %d]", mod_lookup_names[rm], immidiate);
             } else if (mod == 0b01000000) { // Mod = 0b01
+                u8 immidiate = fgetc(src);
+                snprintf(rm_name, sizeof(rm_name), "[%s + %d]", mod_lookup_names[rm], immidiate);
             } else if (mod == 0b00000000) { // Mod = 0b00
+                if (rm == 0b110) { // Direct address
+                    todo("direct address");
+                } else {
+                    snprintf(rm_name, sizeof(rm_name), "[%s]", mod_lookup_names[rm]);
+                }
             }
+
+            if (direction) {
+                fprintf(dst, "mov %s, %s\n", reg_name, rm_name);
+            } else {
+                fprintf(dst, "mov %s, %s\n", rm_name, reg_name);
+            }
+        // Immediate to register
+        } else if ((byte1 & 0b11110000) == 0b10110000) {
+            bool wide = (byte1 & 0b1000) >> 3;
+            u8 reg = byte1 & 0b111;
+
+            u16 immidiate;
+            if (wide) {
+                immidiate = fgetc(src) | (fgetc(src) << 8);
+            } else {
+                immidiate = fgetc(src);
+            }
+
+            fprintf(dst, "mov %s, %d\n", lookup_reg_name(reg, wide), immidiate);
+        } else {
+            todo("unhandled byte %d", byte1);
         }
     }
 }
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