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Add some arithmetics to emulator

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This commit is contained in:
Nero 2019-09-29 12:23:59 +00:00
parent 1ae3c7a0b9
commit bedceb28a4
1 changed files with 53 additions and 4 deletions
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57
utils/emul.c
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@ -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;