Function amo_op

crates/virtual-machine/src/cpu/pipeline/memory.rs:406–475

(
    bus: &mut SystemBus,
    funct5: u8,
    funct3: u8,
    addr: u64,
    val: u64,
)

            0x14 => old_i.max(val_i),          // AMOMAX.W
            0x18 => {
                let old_u = old_w;
                let val_u = val as u32;
                old_u.min(val_u) as i32
            }
            0x1C => {
                let old_u = old_w;
                let val_u = val as u32;
                old_u.max(val_u) as i32
            }
            _ => return Err(VmError::IllegalInstruction(funct5 as u32)),
        };

        bus.write_word(addr, new_i as u32)
            .map_err(|_| VmError::StoreAccessFault(addr))?;

        // Return old value sign-extended
        Ok(old_i as i64 as u64)
    } else {
        // 64-bit AMO
        let old = bus
            .read_doubleword(addr)
            .map_err(|_| VmError::LoadAccessFault(addr))?;
        let old_i = old as i64;
        let val_i = val as i64;

        let new_val: u64 = match funct5 {
            0x00 => old.wrapping_add(val),   // AMOADD.D
            0x01 => val,                     // AMOSWAP.D
            0x04 => old ^ val,               // AMOXOR.D
            0x08 => old | val,               // AMOOR.D
            0x0C => old & val,               // AMOAND.D
            0x10 => old_i.min(val_i) as u64, // AMOMIN.D
            0x14 => old_i.max(val_i) as u64, // AMOMAX.D
            0x18 => old.min(val),            // AMOMINU.D
            0x1C => old.max(val),            // AMOMAXU.D
            _ => return Err(VmError::IllegalInstruction(funct5 as u32)),
        };

        bus.write_doubleword(addr, new_val)
            .map_err(|_| VmError::StoreAccessFault(addr))?;

        Ok(old)
    }
}