only query memory_data/size once per slice

Author: axic

bindings/rust/src/lib.rs

@@ -292,20 +292,19 @@ impl Instance {
     /// Ensure the range is valid according to the currently available memory size.
     fn checked_memory_range(
         &self,
+        memory_data: *mut u8,
+        memory_size: usize,
         offset: u32,
         size: usize,
     ) -> Result<core::ops::Range<usize>, ()> {
         // This is safe given usize::BITS >= u32::BITS, see https://doc.rust-lang.org/std/primitive.usize.html.
         let offset = offset as usize;
         let has_memory = unsafe { sys::fizzy_module_has_memory(self.get_module()) };
-        let memory_size = self.memory_size();
         if !has_memory || offset.checked_add(size).is_none() || (offset + size) > memory_size {
             return Err(());
         }
         // Slices allow empty length, but data must be a valid pointer.
-        debug_assert!(
-            unsafe { sys::fizzy_get_instance_memory_data(self.0.as_ptr()) } != std::ptr::null_mut()
-        );
+        debug_assert!(memory_data != std::ptr::null_mut());
         Ok(offset..offset + size)
     }
 
@@ -314,11 +313,10 @@ impl Instance {
     /// # Safety
     /// These slices turn invalid if the memory is resized (i.e. via the WebAssembly `memory.grow` instruction)
     pub unsafe fn checked_memory_slice(&self, offset: u32, size: usize) -> Result<&[u8], ()> {
-        let range = self.checked_memory_range(offset, size)?;
-        let memory = std::slice::from_raw_parts(
-            sys::fizzy_get_instance_memory_data(self.0.as_ptr()),
-            sys::fizzy_get_instance_memory_size(self.0.as_ptr()),
-        );
+        let memory_data = sys::fizzy_get_instance_memory_data(self.0.as_ptr());
+        let memory_size = sys::fizzy_get_instance_memory_size(self.0.as_ptr());
+        let range = self.checked_memory_range(memory_data, memory_size, offset, size)?;
+        let memory = std::slice::from_raw_parts(memory_data, memory_size);
         Ok(&memory[range])
     }
 
@@ -331,11 +329,10 @@ impl Instance {
         offset: u32,
         size: usize,
     ) -> Result<&mut [u8], ()> {
-        let range = self.checked_memory_range(offset, size)?;
-        let memory = std::slice::from_raw_parts_mut(
-            sys::fizzy_get_instance_memory_data(self.0.as_ptr()),
-            sys::fizzy_get_instance_memory_size(self.0.as_ptr()),
-        );
+        let memory_data = sys::fizzy_get_instance_memory_data(self.0.as_ptr());
+        let memory_size = sys::fizzy_get_instance_memory_size(self.0.as_ptr());
+        let range = self.checked_memory_range(memory_data, memory_size, offset, size)?;
+        let memory = std::slice::from_raw_parts_mut(memory_data, memory_size);
         Ok(&mut memory[range])
     }