1 files changed, 105 insertions, 0 deletions
diff --git a/src/mem.rs b/src/mem.rs
new file mode 100644
index 0000000..297c54c
--- /dev/null
+++ b/src/mem.rs
@@ -0,0 +1,105 @@
+const PAGE_SIZE: usize = 4 * 1024;
+const PAGE_MASK: usize = !(PAGE_SIZE - 1);
+
+struct Page {
+    virtual_addr: usize,
+    real_addr: usize,
+    permission: usize,
+    allocated: usize,
+}
+pub struct Memory {
+    memory: Box<[u8]>,
+    pages: Vec<Page>,
+}
+impl Memory {
+    pub fn new(size: usize) -> Memory {
+        let mut pages: Vec<Page> = Vec::with_capacity(size / PAGE_SIZE);
+        for i in 0..size / PAGE_SIZE {
+            pages[i] = Page {
+                virtual_addr: usize::MAX,
+                real_addr: i * PAGE_SIZE,
+                permission: 0,
+                allocated: 0
+            }
+        }
+        Memory {
+            memory: vec![0u8; size].into_boxed_slice(),
+            pages,
+        }
+    }
+
+    pub fn create_page(&mut self, virtual_addr: usize, permission: usize) -> Option<usize> {
+        // Find first page that isn't allocated and set it to allocated
+        for (i, page) in self.pages.iter_mut().enumerate() {
+            if page.allocated == 0 {
+                page.virtual_addr = virtual_addr;
+                page.permission = permission;
+                page.allocated = 1;
+                return Some(i);
+            }
+        }
+        None
+    }
+
+    pub fn lookup_page(&mut self, virtual_addr: usize, permission: usize) -> Option<usize> {
+        for (i, page) in self.pages.iter().enumerate() {
+            if page.virtual_addr == virtual_addr && permission >= page.permission && page.allocated == 1 {
+                return Some(i);
+            }
+        }
+        return self.create_page(virtual_addr, permission);
+    }
+
+    pub fn ro_lookup(&self, virtual_addr: usize, permission: usize) -> Option<usize> {
+        for (i, page) in self.pages.iter().enumerate() {
+            if page.virtual_addr == virtual_addr && page.permission == permission && page.allocated == 1 {
+                return Some(i);
+            }
+        }
+        None
+    }
+
+    pub fn write(&mut self, address: usize, permission: usize, value: u8) -> Result<(), ()> {
+        let page = address & PAGE_MASK;
+        let offset = address - page;
+
+        if let Some(page) = self.lookup_page(address, permission) {
+            self.memory[self.pages[page].real_addr + offset] = value;
+            Ok(())
+        } else {
+            Err(())
+        }
+    }
+
+    pub fn read(&self, address: usize, permission: usize) -> Result<u8, ()> {
+        let page = address & PAGE_MASK;
+        let offset = address - page;
+
+        if let Some(page) = self.ro_lookup(address, permission) {
+            Ok(self.memory[self.pages[page].real_addr + offset])
+        } else {
+            Err(())
+        }
+    }
+    
+    pub fn read_multiple_bytes(&self, address: usize, size: usize, permission: usize) -> Result<Box<[u8]>, ()> {
+        let mut ret = [];
+        for addr in  address..address+size {
+            if let Ok(byte) = self.read(addr, permission) {
+                ret[addr - address] = byte;
+            } else {
+                return Err(());
+            }
+        }
+        Ok(Box::new(ret))
+    }
+    
+    pub fn write_multiple_bytes(&mut self, address: usize, bytes: &[u8], permission: usize) -> Result<(), ()> {
+        for addr in address..address + bytes.len() {
+            if let Err(_) = self.write(addr, permission, bytes[addr - address]) {
+                return Err(());
+            } 
+        }
+        Ok(())
+    }
+}
+\ No newline at end of file