ft(interpreter): impl short jumps

src/disasm.rs

@@ -184,32 +184,34 @@ impl Disassembler {
     /// offset.
     /// Returns the read byte added to the address of the subsequent instruction
     /// to act as a relative offset (Intel Jb operand).
-    fn parse_j_byte(&mut self) -> Result<isize, DisasmError> {
+    /// The returned `usize` will be the subsequent instruction to jump to.
+    fn parse_j_byte(&mut self) -> Result<usize, DisasmError> {
         log::debug!("Attempting to parse Jb at {:#04x} ...", self.offset);
         // first interpret as 2-complement, then cast for addition
         let byte = self.parse_byte()? as IByte as isize;
         let next_addr = (self.offset + 1) as isize;
         log::debug!(
             "Parsed Jb consists of {byte:#04x} + {next_addr:#04x} = {:#04x}",
-            byte + next_addr
+            (byte + next_addr) as usize
         );
-        Ok(byte + next_addr)
+        Ok((byte + next_addr) as usize)
     }
 
     /// Parse a word of the binary, interpret it as signed and advance the
     /// offset.
     /// Returns the read word added to the address of the subsequent instruction
     /// to act as a relative offset (Intel Jw/Jv operand).
-    pub fn parse_j_word(&mut self) -> Result<isize, DisasmError> {
+    /// The returned `usize` will be the subsequent instruction to jump to.
+    pub fn parse_j_word(&mut self) -> Result<usize, DisasmError> {
         log::debug!("Attempting to parse Jv at {:#04x} ...", self.offset);
         // first interpret as 2-complement, then cast for addition
         let word = self.parse_word()? as IWord as isize;
         let next_addr = (self.offset + 1) as isize;
         log::debug!(
             "Parsed Jv consists of {word:#04x} + {next_addr:#04x} = {:#04x}",
-            word + next_addr
+            (word + next_addr) as usize
         );
-        Ok(word + next_addr)
+        Ok((word + next_addr) as usize)
     }
 
     /// Parse a single pointer of the binary and advance the offset.