diff --git a/prefetcher_reverse/src/ip_tool.rs b/prefetcher_reverse/src/ip_tool.rs
index 346c030..dcbf0f8 100644
--- a/prefetcher_reverse/src/ip_tool.rs
+++ b/prefetcher_reverse/src/ip_tool.rs
@@ -2,9 +2,12 @@ use bitvec::prelude::*;
 use cache_utils::mmap::MMappedMemory;
 use lazy_static::lazy_static;
 use std::collections::LinkedList;
+use std::ptr::copy_nonoverlapping;
 use std::sync::Mutex;
 
 struct WXRange {
+    start: usize,
+    end: usize,     // points to the last valid byte
     bitmap: BitVec, // fixme bit vector
     pages: Vec<MMappedMemory<u8>>,
 }
@@ -50,8 +53,91 @@ const TIMED_CLFLUSH: FunctionTemplate = FunctionTemplate {
     end: timed_clflush_template_end as *const u8,
 };
 
-pub fn allocate_function(align: usize, template: FunctionTemplate) -> Function {
-    unimplemented!()
+impl WXRange {
+    unsafe fn allocate(
+        &mut self,
+        align: usize,
+        offset: usize,
+        length: usize,
+        mask: usize,
+        round_mask: usize,
+    ) -> Result<*mut u8, ()> {
+        // In each range, we want to find base = 2^a * k such that start <= base + align < start + 2^a
+        // This can be done with k = ceil(start - align / 2^a).
+        // 2^a * k can likely be computed with some clever bit tricks.
+        // \o/
+        let start = self.start;
+        let mut candidate = (start - offset + mask) & round_mask + offset;
+        assert_eq!(candidate & mask, offset);
+        assert!(candidate > start);
+        while candidate + length <= self.end {
+            let bit_range = &mut self.bitmap[(candidate - start)..(candidate - start + length)];
+            if !bit_range.any() {
+                bit_range.set_all(true);
+                return Ok(candidate as *mut u8);
+            }
+            candidate += align;
+        }
+        Err(())
+    }
+}
+
+impl WXAllocator {
+    pub unsafe fn allocate(
+        &mut self,
+        align: usize,
+        offset: usize,
+        length: usize,
+    ) -> Result<*mut u8, ()> {
+        if align.count_ones() != 1 && offset < align {
+            return Err(()); // FIXME Error type.
+        }
+        let mask = align - 1;
+        let round_mask = !mask;
+        for range in self.ranges.iter_mut() {
+            if let Ok(p) = unsafe { range.allocate(align, offset, length, mask, round_mask) } {
+                return Ok(p);
+            }
+        }
+        // Now we need to allocate a new page ^^'
+        return Err(());
+    }
+}
+
+impl Function {
+    pub fn try_new(
+        align: usize,
+        offset: usize,
+        template: FunctionTemplate,
+    ) -> Result<Function, ()> {
+        // find suitable target
+        let mut allocator = wx_allocator.lock().unwrap();
+        if align.count_ones() != 1 && offset < align {
+            return Err(()); // FIXME Error type.
+        }
+        let mask = align - 1;
+        let real_offset = (offset - (template.ip as usize) + (template.start as usize)) & mask;
+        let length = (template.end as usize) - (template.start as usize);
+
+        let p = unsafe { allocator.allocate(align, real_offset, length) }?;
+        unsafe { copy_nonoverlapping(template.start as *const u8, p, length) };
+        let res = Function {
+            fun: unsafe {
+                std::mem::transmute::<*mut u8, unsafe extern "C" fn(*const u8) -> u64>(p)
+            },
+            ip: unsafe { p.add(template.ip as usize - template.start as usize) },
+            end: unsafe { p.add(length) },
+            size: length,
+        };
+        Ok(res)
+    }
+}
+
+impl Drop for Function {
+    fn drop(&mut self) {
+        // Find the correct range, and deallocate all the bits
+        todo!()
+    }
 }
 
 global_asm!(