avm2: Don't mutably borrow for pos()

core/src/avm2/activation.rs

@@ -2393,14 +2393,14 @@ impl<'a, 'gc, 'gc_context> Activation<'a, 'gc, 'gc_context> {
     ) -> Result<FrameControl<'gc>, Error> {
         let index = self.context.avm2.pop().coerce_to_i32(self)?;
 
-        //TODO: can we just subtract the size of *this* op to save some of this maths
         let offset = case_offsets
             .get(index as usize)
             .copied()
             .unwrap_or(default_offset)
-            + current_pos as i32;
-        let current_pos = reader.pos(full_data) as i32;
-        reader.seek(full_data, offset - current_pos);
+            + current_pos as i32
+            - reader.pos(full_data) as i32;
+
+        reader.seek(full_data, offset);
 
         Ok(FrameControl::Continue)
     }

swf/src/avm1/read.rs

@@ -15,6 +15,11 @@ impl<'a> ReadSwfExt<'a> for Reader<'a> {
     fn as_mut_slice(&mut self) -> &mut &'a [u8] {
         &mut self.input
     }
+
+    #[inline(always)]
+    fn as_slice(&self) -> &'a [u8] {
+        &self.input
+    }
 }
 
 impl<'a> Reader<'a> {

swf/src/avm2/read.rs

@@ -12,6 +12,11 @@ impl<'a> ReadSwfExt<'a> for Reader<'a> {
     fn as_mut_slice(&mut self) -> &mut &'a [u8] {
         &mut self.input
     }
+
+    #[inline(always)]
+    fn as_slice(&self) -> &'a [u8] {
+        &self.input
+    }
 }
 
 impl<'a> Reader<'a> {

swf/src/extensions.rs

@@ -6,9 +6,15 @@ use std::io::{self, Read};
 pub trait ReadSwfExt<'a> {
     fn as_mut_slice(&mut self) -> &mut &'a [u8];
 
+    fn as_slice(&self) -> &'a [u8];
+
+    fn pos(&self, data: &[u8]) -> usize {
+        self.as_slice().as_ptr() as usize - data.as_ptr() as usize
+    }
+
     // TODO: Make this fallible?
     fn seek(&mut self, data: &'a [u8], relative_offset: isize) {
-        let mut pos = self.as_mut_slice().as_ptr() as usize - data.as_ptr() as usize;
+        let mut pos = self.pos(data);
         pos = (pos as isize + relative_offset) as usize;
         pos = pos.min(data.len());
         *self.as_mut_slice() = &data[pos..];

swf/src/read.rs

@@ -243,6 +243,11 @@ impl<'a> ReadSwfExt<'a> for Reader<'a> {
     fn as_mut_slice(&mut self) -> &mut &'a [u8] {
         &mut self.input
     }
+
+    #[inline(always)]
+    fn as_slice(&self) -> &'a [u8] {
+        &self.input
+    }
 }
 
 impl<'a> Reader<'a> {