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arm: Fix bug when calculating 24bit branch offsets, and add a test for

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it.
This commit is contained in:
Michel Heily 2019-06-28 12:01:49 +03:00
parent d11620e65b
commit 7898bf61f3
1 changed files with 20 additions and 2 deletions
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22
src/arm7tdmi/arm/mod.rs
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@ -295,7 +295,7 @@ impl ArmInstruction {
} }
pub fn branch_offset(&self) -> i32 { pub fn branch_offset(&self) -> i32 {
((self.raw.bit_range(0..24) << 2) as i32) + 8 (((self.raw.bit_range(0..24) << 8) as i32) >> 6).wrapping_add(8)
} }
pub fn load_flag(&self) -> bool { pub fn load_flag(&self) -> bool {
@ -437,10 +437,28 @@ mod tests {
use super::*; use super::*;
#[test] #[test]
fn test_swi() { fn test_decode_swi() {
// swi #0x1337 // swi #0x1337
let decoded = ArmInstruction::try_from(0xef001337).unwrap(); let decoded = ArmInstruction::try_from(0xef001337).unwrap();
assert_eq!(decoded.fmt, ArmInstructionFormat::SWI); assert_eq!(decoded.fmt, ArmInstructionFormat::SWI);
assert_eq!(decoded.swi_comment(), 0x1337); assert_eq!(decoded.swi_comment(), 0x1337);
} }
#[test]
fn test_decode_branch_forwards() {
// 0x20: b 0x30
let decoded = ArmInstruction::try_from((0xea_00_00_02, 0x20)).unwrap();
assert_eq!(decoded.fmt, ArmInstructionFormat::B_BL);
assert_eq!(decoded.link_flag(), false);
assert_eq!((decoded.pc as i32).wrapping_add(decoded.branch_offset()), 0x30);
}
#[test]
fn test_decode_branch_backwards() {
// 0x20: bl 0x10
let decoded = ArmInstruction::try_from((0xeb_ff_ff_fa, 0x20)).unwrap();
assert_eq!(decoded.fmt, ArmInstructionFormat::B_BL);
assert_eq!(decoded.link_flag(), true);
assert_eq!((decoded.pc as i32).wrapping_add(decoded.branch_offset()), 0x10);
}
} }