1 files changed, 13 insertions, 11 deletions

diff --git a/src/isa/mod.rs b/src/isa/mod.rs
index 086df74..6519a34 100644
--- a/src/isa/mod.rs
+++ b/src/isa/mod.rs
@@ -4,6 +4,8 @@ pub mod funct7;
 
 pub type Word = u32;
 pub type SignedWord = i32;
+
+// TODO: directly encode PC as u32, as architecturally specified
 pub type Address = usize;
 
 #[derive(Debug, PartialEq)]
@@ -128,31 +130,31 @@ impl Instruction {
         Register::from_num((self.word >> 20) & 0x1F)
     }
 
-    pub fn i_imm(&self) -> i32 {
-        (self.word as i32) >> 20
+    pub fn i_imm(&self) -> SignedWord {
+        (self.word as SignedWord) >> 20
     }
 
-    pub fn s_imm(&self) -> i32 {
+    pub fn s_imm(&self) -> SignedWord {
         let low = (self.word >> 7) & 0x1F;
-        let high = (((self.word as i32) >> 25) & 0x7F) as u32;
-        ((high << 7) | low) as i32
+        let high = (((self.word as SignedWord) >> 25) & 0x7F) as Word;
+        ((high << 7) | low) as SignedWord
     }
 
-    pub fn uj_imm(&self) -> i32 {
+    pub fn uj_imm(&self) -> SignedWord {
         // Want zero-extension
         let low1 = (self.word >> 21) & 0x3FF;
         let low11 = (self.word >> 20) & 0x1;
         let low12 = (self.word >> 12) & 0xFF;
         // Want sign-extension
-        let low20 = (((self.word as i32) >> 30) & 0x1) as u32;
-        ((low20 << 20) | (low12 << 12) | (low11 << 11) | (low1 << 1)) as i32
+        let low20 = (((self.word as SignedWord) >> 30) & 0x1) as Word;
+        ((low20 << 20) | (low12 << 12) | (low11 << 11) | (low1 << 1)) as SignedWord
     }
 
-    pub fn sb_imm(&self) -> i32 {
+    pub fn sb_imm(&self) -> SignedWord {
         let low1 = (self.word >> 8) & 0xF;
         let low5 = (self.word >> 25) & 0x3F;
         let low11 = (self.word >> 7) & 0x1;
-        let low12 = (((self.word as i32) >> 31) & 0x1) as u32;
-        ((low12 << 12) | (low11 << 11) | (low5 << 5) | (low1 << 1)) as i32
+        let low12 = (((self.word as SignedWord) >> 31) & 0x1) as Word;
+        ((low12 << 12) | (low11 << 11) | (low5 << 5) | (low1 << 1)) as SignedWord
     }
 }