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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(())
}
}
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