From 2a3f0b3bb3affaefaef3bcb04eaa8797ba13361b Mon Sep 17 00:00:00 2001
From: Quentin Legot <legotquentin@gmail.com>
Date: Wed, 9 Nov 2022 17:31:14 +0100
Subject: [PATCH] Fix decode to allow overflow in certains cases, add a case in
 test for riscv_lui where imm is negative

---
 src/decode.rs | 8 +++++---
 src/print.rs  | 2 ++
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/decode.rs b/src/decode.rs
index 3ef5bdb..68d0e2f 100644
--- a/src/decode.rs
+++ b/src/decode.rs
@@ -1,3 +1,5 @@
+use core::num::Wrapping; // Permet d'autoriser les overflow pour les opérations voulues
+
 #[allow(non_snake_case)] // supprimer le warning snake case (quand les noms de variables ont des majuscules)
 #[derive(Debug)] 
 pub struct Instruction {
@@ -45,8 +47,8 @@ pub fn decode(val : u32) -> Instruction {
     let imm12_I         = ((val >> 20) & 0xfff) as u16;
     let imm12_S         = (((val >> 20) & 0xfe0) + ((val >> 7) & 0x1f)) as u16;
     
-    let imm12_I_signed  = if imm12_I >= 2048 { imm12_I - 4096 } else { imm12_I } as i16;
-    let imm12_S_signed  = if imm12_S >= 2048 { imm12_S - 4096 } else { imm12_S } as i16;
+    let imm12_I_signed  = if imm12_I >= 2048 { (Wrapping(imm12_I) - Wrapping(4096)).0 } else { imm12_I } as i16;
+    let imm12_S_signed  = if imm12_S >= 2048 { (Wrapping(imm12_S) - Wrapping(4096)).0 } else { imm12_S } as i16;
     
     let imm13           = (((val >> 19) & 0x1000) + ((val >> 20) & 0x7e0) +
                         ((val >> 7) & 0x1e) + ((val << 4) & 0x800)) as i16;
@@ -57,7 +59,7 @@ pub fn decode(val : u32) -> Instruction {
     
     let imm21_1         = ((val & 0xff000) + ((val >> 9) & 0x800) +
                         ((val >> 20) & 0x7fe) + ((val >> 11) & 0x100000)) as u32;
-    let imm21_1_signed  = if imm21_1 >= 1048576 { imm21_1 - 2097152 } else { imm21_1 } as i32;
+    let imm21_1_signed  = if imm21_1 >= 1048576 { (Wrapping(imm21_1) - Wrapping(2097152)).0 } else { imm21_1 } as i32;
     
     let shamt           = ((val >> 20) & 0x3f) as u8;
     
diff --git a/src/print.rs b/src/print.rs
index 3e4eb00..aac1952 100644
--- a/src/print.rs
+++ b/src/print.rs
@@ -299,7 +299,9 @@ mod test {
     #[test]
     fn test_lui() {
         let lui = decode::decode(0b01110001000011111000_11100_0110111);
+        let lui_negatif = decode::decode(0b11110001000011111000_11100_0110111);
         assert_eq!("lui x28, 0x710F8000", print::print(lui, 0));
+        assert_eq!("lui x28, 0xF10F8000", print::print(lui_negatif, 0));
     }
 
     #[test]