fix: correctly add displacement for short jumps

src/disasm.rs

@@ -634,12 +634,24 @@ impl Disassembler {
 
                 0xE8 => Mnemonic::CALL_v(self.parse_word()),
 
-                0xE9 => Mnemonic::JMP_v(self.parse_word()),
+                // add to address of next instruction
+                0xE9 => {
+                    // first interpret as IByte, then cast for addition
+                    let word = self.parse_word() as IByte as isize;
+                    let next_addr = (self.offset + 1) as isize;
+                    Mnemonic::JMP_v(next_addr + word)
+                }
                 0xEA => Mnemonic::JMP_p(Pointer {
                     segment: self.parse_word(),
                     offset: self.parse_word(),
                 }),
-                0xEB => Mnemonic::JMP_b(self.parse_byte()),
+                // add to address of next instruction
+                0xEB => {
+                    // first interpret as IByte, then cast for addition
+                    let byte = self.parse_byte() as IByte as isize;
+                    let next_addr = (self.offset + 1) as isize;
+                    Mnemonic::JMP_b(next_addr + byte)
+                }
 
                 0xEC => Mnemonic::IN_ALDX,
                 0xED => Mnemonic::IN_AXDX,

src/instructions.rs

@@ -235,8 +235,8 @@ pub enum Mnemonic {
     CALL_Mod(ModRmTarget),
     // JUMP
     JMP_p(Pointer),
-    JMP_b(Byte),
-    JMP_v(Word),
+    JMP_b(isize), // parses IByte, but stores as isize
+    JMP_v(isize), // parwses IWord, but stores as isize
     JMP_Mod(ModRmTarget),
     // WAIT
     WAIT,