emu: CBW/CWD sign extension operations

src/emu/i8088.rs

@@ -588,6 +588,8 @@ impl i8088 {
           0x95 => xchg[reg=a, reg=bp] / 3,  // XCHG ax, bp
           0x96 => xchg[reg=a, reg=si] / 3,  // XCHG ax, si
           0x97 => xchg[reg=a, reg=di] / 3,  // XCHG ax, di
+          0x98 => cbw[reg=a, reglo=a] / 2,  // CBW
+          0x99 => cwd[reg=d, reg=a] / 5,    // CWD
           0x9C => push[bus, regval=ss, reg=sp, flags] / 14,  // PUSHF
           0x9D => pop[bus, regval=ss, reg=sp, flags] / 12,   // POPF
           // 0x9E SAHF not implemented

src/emu/operations.rs

@@ -6,7 +6,7 @@ use emu::num_traits::CheckedShr;
 use emu::dos;
 use emu::flags::{FlagOp, Flags};
 use emu::i8088::{RepPrefix, i8088};
-use emu::operands::{Address, DynLValue, FarPtr, LValue, Operand, Reg, RValue};
+use emu::operands::{Address, DynLValue, FarPtr, LValue, Operand, Reg, RegLo, RValue};
 use emu::pc::Bus;
 
 macro_rules! string_op {
@@ -101,6 +101,10 @@ pub fn call(mut ip: Reg, bus: &mut Bus, ss: u16, sp: Reg, rel16: u16) {
   ip.write(target);
 }
 
+pub fn cbw(mut ax: Reg, al: RegLo) {
+  ax.write(al.read() as i8 as u16);
+}
+
 pub fn clc(flags: &mut Flags) {
   flags.update(FlagOp::Eager { cf: false,
                                pf: flags.pf(),
@@ -152,6 +156,10 @@ where T: Operand + RValue<T>,
   });
 }
 
+pub fn cwd(mut dx: Reg, ax: Reg) {
+  dx.write(if ax.read() < 0x8000 { 0x0000 } else { 0xFFFF });
+}
+
 pub fn dec<T: Operand, LVal: LValue<T>>(flags: &mut Flags, mut dst: LVal) {
   let dst_before = dst.read();
   let res = dst_before.wrapping_sub(&T::one());