From bedceb28a4a3e5bbcd0b2a1f8b438e27c868bc2c Mon Sep 17 00:00:00 2001
From: Ain <41307858+nero@users.noreply.github.com>
Date: Sun, 29 Sep 2019 12:23:59 +0000
Subject: [PATCH] Add some arithmetics to emulator

---
 utils/emul.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 53 insertions(+), 4 deletions(-)

diff --git a/utils/emul.c b/utils/emul.c
index b5e59f2..1f8bc09 100644
--- a/utils/emul.c
+++ b/utils/emul.c
@@ -10,8 +10,9 @@ union regset {
    uint16_t r16[8]; // AX, CX, DX, BX, SP, BP, SI, DI
 } regset;
 
+int carry, zero;
+
 uint16_t ip = 0x100;
-uint16_t flags;
 uint16_t scratch;
 uint16_t reg;
 int off;
@@ -23,7 +24,6 @@ void* rmptr;
 #define R8(x) regset.r8[fixr8ref(x)]
 #define R16(x) regset.r16[x]
 
-#define syscall_number regset.r8[4]
 #define AL regset.r8[0]
 #define CL regset.r8[2]
 #define DL regset.r8[4]
@@ -34,6 +34,16 @@ void* rmptr;
 #define SI regset.r16[6]
 #define DI regset.r16[7]
 
+#define ADD 0
+#define OR  1
+#define ADC 2
+#define SBB 3
+#define AND 4
+#define SUB 5
+#define XOR 6
+#define CMP 7
+#define TEST 8
+
 const char* const regnames[] = { "AX", "CX", "DX", "BX", "SP", "BP", "SI", "DI", 0 };
 
 // Dump registers
@@ -47,6 +57,32 @@ void dump() {
   printf("IP=%04X : %X\n", ip, mem[ip]);
 }
 
+void arith16(int op, int16_t* dst, int src) {
+  // I'll just assume this sign-extends
+  int t = *dst;
+  int p = *dst;
+  switch (op) {
+  case ADD:  t += src; break;
+  case OR:   t |= src; break;
+  case ADC:  t += (src + carry); break;
+  case SBB:  t -= (src + carry); break;
+  case AND:  t &= src; break;
+  case SUB:  t -= src; break;
+  case XOR:  t ^= src; break;
+  case CMP:  t -= src; break;
+  case TEST: t &= src; break;
+  }
+  zero=!t;
+  // I dont think the following is correct
+  carry=((t ^ p) >> 16) & 1;
+  if (op==CMP || op==TEST) return;
+  *dst = t;
+}
+
+uint16_t get_flags() {
+  return (carry & 1) | ((zero & 1)<< 6);
+}
+
 int fixr8ref(int r) {
   return ((r << 1) & 0b110) | ((r >> 2) & 0b1);
 }
@@ -71,7 +107,7 @@ void modrm(int size) {
   uint8_t rm = (mem[ip]) & 0b111;
   ip++;
   if (mod == 3) {
-    if (size == BIT8) {
+    if (size == BIT16) {
       rmptr = &R16(rm);
     } else {
       rmptr = &R8(rm);
@@ -156,15 +192,25 @@ void step() {
   uint8_t opcode = mem[ip];
   ip++;
   switch(opcode) {
+  case 0x50 ... 0x57: // PUSH reg16
+    push(R16(opcode-0x50));
+    break;
+  case 0x58 ... 0x5F: // POP reg16
+    R16(opcode-0x58)=pop();
+    break;
   case 0x70 ... 0x7F: // Jcc
     reg = ip + (int8_t)imm8();
     if (cond(opcode-0x70)) {
       ip = reg;
     }
     break;
+  case 0x83: // ARITH r/m16,imm8
+    modrm(BIT16);
+    arith16(reg, &RM16, imm8());
+    break;
   case 0x84: // TEST r/m8,reg8
     modrm(BIT8);
-    scratch = AL & RM8;
+    scratch = R8(reg) & RM8;
     break;
   case 0x88: // MOV r/m8,reg8
     modrm(BIT8);
@@ -174,6 +220,9 @@ void step() {
     modrm(BIT16);
     R16(reg) = RM16;
     break;
+  case 0x9C: // PUSHF
+    push(get_flags());
+    break;
   case 0xA1: // MOV AX,memoffs16
     AX = *(uint16_t*)&mem[imm16()];
     break;