From 7cdf6c09182eead1edafcc82e1c4baca65bc662d Mon Sep 17 00:00:00 2001
From: Astro <astro@spaceboyz.net>
Date: Mon, 28 Oct 2019 00:43:57 +0100
Subject: [PATCH] start implementation of a StaticAllocator

---
 src/main.rs |  1 +
 src/ram.rs  | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 76 insertions(+)
 create mode 100644 src/ram.rs

diff --git a/src/main.rs b/src/main.rs
index 27d351f..c98314e 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -20,6 +20,7 @@ mod regs;
 mod cortex_a9;
 mod stdio;
 mod zynq;
+mod ram;
 
 use crate::regs::{RegisterR, RegisterW};
 use crate::cortex_a9::{asm, regs::*, mmu};
diff --git a/src/ram.rs b/src/ram.rs
new file mode 100644
index 0000000..767392b
--- /dev/null
+++ b/src/ram.rs
@@ -0,0 +1,75 @@
+use core::mem::{align_of, size_of};
+
+pub trait RAM {
+    #[inline(always)]
+    fn addr(&self) -> usize;
+    #[inline(always)]
+    fn size(&self) -> usize;
+
+    #[inline(always)]
+    fn into_memory_region(&self) -> MemoryRegion {
+        MemoryRegion {
+            addr: self.addr(),
+            size: self.size(),
+        }
+    }
+
+}
+
+pub struct MemoryRegion {
+    addr: usize,
+    size: usize,
+}
+
+impl MemoryRegion {
+    #[inline(always)]
+    fn split(&mut self, offset: usize) -> MemoryRegion {
+        if offset > self.size {
+            panic!("StaticAllocator: unable to split {}/{} bytes", offset, self.size);
+        }
+        
+        let result = MemoryRegion {
+            addr: self.addr,
+            size: offset,
+        };
+        self.addr += offset;
+        self.size -= offset;
+        result
+    }
+
+    unsafe fn clear<T>(self) -> *mut T {
+        let result = self.addr as *mut T;
+        for b in core::slice::from_raw_parts_mut::<u8>(result as *mut u8, self.size) {
+            *b = 0;
+        }
+        result
+    }
+
+    pub fn align(&mut self, alignment: usize) {
+        let mask = alignment - 1;
+        let addr = (self.addr | mask) + 1;
+        self.size -= addr - self.addr;
+        self.addr = addr;
+    }
+}
+
+pub struct StaticAllocator {
+    free: MemoryRegion,
+}
+
+impl StaticAllocator {
+    pub fn new<R: RAM>(r: R) -> Self {
+        StaticAllocator {
+            free: r.into_memory_region(),
+        }
+    }
+
+    pub fn alloc<'a: 'b, 'b, T: Sized>(&'a mut self) -> &'b mut T {
+        self.free.align(align_of::<T>());
+
+        let size = size_of::<T>();
+        let region = self.free.split(size);
+
+        unsafe { &mut *region.clear() }
+    }
+}