From 9bce345a3b709342d9e5a0a6e0aedca716c7c540 Mon Sep 17 00:00:00 2001
From: Ain <41307858+nero@users.noreply.github.com>
Date: Fri, 4 Oct 2019 22:54:37 +0000
Subject: [PATCH] Add string prefixes and inc/dec to emulator

---
 utils/emul.c | 63 +++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 47 insertions(+), 16 deletions(-)

diff --git a/utils/emul.c b/utils/emul.c
index f076cd4..8072d81 100644
--- a/utils/emul.c
+++ b/utils/emul.c
@@ -36,8 +36,8 @@ union flags {
 
 uint16_t ip = 0x100;
 uint16_t scratch;
+uint16_t prefixes = 0;
 uint16_t reg;
-int off;
 
 void* rmptr;
 #define RM8 *(uint8_t*)rmptr
@@ -46,28 +46,20 @@ void* rmptr;
 #define R8(x) regset.r8[fixr8ref(x)]
 #define R16(x) regset.r16[x]
 
-#define FLAGMASK 0xF02A
-#define CF 0
-#define PF 2
-#define AF 4
-#define ZF 6
-#define SF 7
-#define TF 8
-#define IF 9
-#define DF 10
-#define OF 11
-
 #define AL regset.r8[0]
 #define AH regset.r8[1]
 #define CL regset.r8[2]
 #define DL regset.r8[4]
 #define AX regset.r16[0]
+#define CX regset.r16[1]
 #define BX regset.r16[3]
 #define SP regset.r16[4]
 #define BP regset.r16[5]
 #define SI regset.r16[6]
 #define DI regset.r16[7]
 
+#define FLAGMASK 0xF02A
+
 #define ADD 0
 #define OR  1
 #define ADC 2
@@ -78,6 +70,9 @@ void* rmptr;
 #define CMP 7
 #define TEST 8
 
+#define PREFIX_REPE	1
+#define PREFIX_REPNE	2
+
 const char* const regnames[] = { "AX", "CX", "DX", "BX", "SP", "BP", "SI", "DI", 0 };
 
 // Dump registers
@@ -272,6 +267,14 @@ void step() {
     modrm(BIT16);
     arith16(opcode >> 3, &RM16, R16(reg));
     break;
+  case 0x40 ... 0x47: // INC reg16
+    R16(opcode - 0x40)++;
+    flags.bit.z=!R16(opcode - 0x40);
+    break;
+  case 0x48 ... 0x4F: // DEC reg16
+    R16(opcode - 0x48)--;
+    flags.bit.z=!R16(opcode - 0x48);
+    break;
   case 0x50 ... 0x57: // PUSH reg16
     push(R16(opcode-0x50));
     break;
@@ -320,9 +323,27 @@ void step() {
   case 0xA1: // MOV AX,memoffs16
     AX = *(uint16_t*)&mem[imm16()];
     break;
+  case 0xAA: // STOSB
+    scratch = 1;
+    if (prefixes & PREFIX_REPE) {
+      scratch = CX;
+      CX = 0;
+    }
+    for(;scratch>0;scratch--) {
+      mem[DI] = AL;
+      DI += 1 - (flags.bit.d << 1);
+    }
+    break;
   case 0xAC: // LODSB
-    AL = mem[SI];
-    SI++;
+    scratch = 1;
+    if (prefixes & PREFIX_REPE) {
+      scratch = CX;
+      CX = 0;
+    }
+    for(;scratch>0;scratch--) {
+      AL = mem[SI];
+      SI += 1 - (flags.bit.d << 1);
+    }
     break;
   case 0xB0 ... 0xB7: // MOV reg8,imm8
     reg = opcode-0xB0;
@@ -357,9 +378,18 @@ void step() {
   case 0xEB: // JMP rb
     ip = ip + (int8_t)imm8();
     break;
+  case 0xF2:
+    prefixes |= PREFIX_REPNE;
+    return;
+  case 0xF3:
+    prefixes |= PREFIX_REPE;
+    return;
   case 0xFA: // CLI
+    flags.bit.i = 0;
+    break;
   case 0xFB: // STI
-    break; // no-op, since we dont have interrupts
+    flags.bit.i = 1;
+    break;
   default:
     ip--;
     dump();
@@ -367,6 +397,8 @@ void step() {
     exit(1);
     break;
   }
+  prefixes = 0;
+  if (flags.bit.t) dump();
 }
 
 void copy_cmdline(char* str) {
@@ -427,6 +459,5 @@ int main(int argc, char** argv) {
 
   while(1) {
     step();
-    if (flags.bit.t) dump();
   }
 }