From 7ffec2b2ffe4246a6fe63f5b59ca399ae236236f Mon Sep 17 00:00:00 2001
From: David Li <li.davidm96@gmail.com>
Date: Sun, 3 Jan 2016 10:40:01 -0700
Subject: Fix write_byte, add basic tests

---
 src/lib.rs    | 23 ++++++++++++++++++++++-
 src/memory.rs |  7 +++----
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index f5bf110..ebbc92f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -14,7 +14,7 @@
 // You should have received a copy of the GNU General Public License
 // along with rustv.  If not, see <http://www.gnu.org/licenses/>.
 
-#![feature(associated_consts)]
+#![feature(step_by)]
 pub mod isa;
 pub mod binary;
 pub mod memory;
@@ -57,4 +57,25 @@ mod tests {
         assert_eq!(dm_cache_doubleword.parse_address(0xFFFFFFFD),
                    (0x7FFFFFF, 3, 5));
     }
+
+    #[test]
+    fn memory_rw() {
+        use memory::*;
+        let size = 0xFF;
+        let mut memory = Memory::new(size);
+
+        assert_eq!(memory.write_word(0, 0xF0),
+                   Err(MemoryError::InvalidAddress));
+        assert_eq!(memory.write_byte(0, 0xF0),
+                   Err(MemoryError::InvalidAddress));
+        assert_eq!(memory.write_byte(1, 0xF0),
+                   Err(MemoryError::InvalidAddress));
+        assert_eq!(memory.write_byte(2, 0xF0),
+                   Err(MemoryError::InvalidAddress));
+
+        for address in (4..size).step_by(4) {
+            assert_eq!(memory.write_word(address, 0xF0), Ok(()));
+            assert_eq!(memory.read_word(address), Ok(0xF0));
+        }
+    }
 }
diff --git a/src/memory.rs b/src/memory.rs
index 22d9bce..9b4ab0a 100644
--- a/src/memory.rs
+++ b/src/memory.rs
@@ -20,7 +20,7 @@ use std::cell::RefCell;
 use isa::{self, Instruction};
 use binary::{Binary};
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, PartialEq)]
 pub enum MemoryError {
     InvalidAddress,
     CacheMiss {
@@ -65,7 +65,6 @@ pub trait MemoryInterface {
     }
 
     fn write_byte(&mut self, address: isa::Address, value: isa::Byte) -> Result<()> {
-        let address = address / 4;
         let offset = address % 4;
 
         let result = self.read_word(address);
@@ -73,14 +72,14 @@ pub trait MemoryInterface {
 
         match result {
             Ok(word) => {
-                match offset {
+                let value = match offset {
                     0 => (word & !(0xFF)) | value,
                     1 => (word & !(0xFF00)) | (value << 8),
                     2 => (word & !(0xFF0000)) | (value << 16),
                     3 => (word & !(0xFF000000)) | (value << 24),
                     _ => panic!(""),
                 };
-                Ok(())
+                self.write_word(address, value)
             },
             Err(e) => Err(e),
         }
-- 
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