diff --git a/whisper/__init__.py b/whisper/__init__.py
index e210718f3..afb7a2e78 100644
--- a/whisper/__init__.py
+++ b/whisper/__init__.py
@@ -60,11 +60,20 @@ def _download(url: str, root: str, in_memory: bool) -> Union[bytes, str]:
     if os.path.exists(download_target) and not os.path.isfile(download_target):
         raise RuntimeError(f"{download_target} exists and is not a regular file")
 
+    def compute_sha256(file_path: str) -> str:
+        sha256 = hashlib.sha256()
+        with open(file_path, "rb") as f:
+            for chunk in iter(lambda: f.read(8192), b""):
+                sha256.update(chunk)
+        return sha256.hexdigest()
+
     if os.path.isfile(download_target):
-        with open(download_target, "rb") as f:
-            model_bytes = f.read()
-        if hashlib.sha256(model_bytes).hexdigest() == expected_sha256:
-            return model_bytes if in_memory else download_target
+        if compute_sha256(download_target) == expected_sha256:
+            if in_memory:
+                with open(download_target, "rb") as f:
+                    return f.read()
+            else:
+                return download_target
         else:
             warnings.warn(
                 f"{download_target} exists, but the SHA256 checksum does not match; re-downloading the file"
@@ -86,13 +95,16 @@ def _download(url: str, root: str, in_memory: bool) -> Union[bytes, str]:
                 output.write(buffer)
                 loop.update(len(buffer))
 
-    model_bytes = open(download_target, "rb").read()
-    if hashlib.sha256(model_bytes).hexdigest() != expected_sha256:
+    if compute_sha256(download_target) != expected_sha256:
         raise RuntimeError(
             "Model has been downloaded but the SHA256 checksum does not not match. Please retry loading the model."
         )
 
-    return model_bytes if in_memory else download_target
+    if in_memory:
+        with open(download_target, "rb") as f:
+            return f.read()
+    else:
+        return download_target
 
 
 def available_models() -> List[str]:
@@ -147,7 +159,7 @@ def load_model(
     with (
         io.BytesIO(checkpoint_file) if in_memory else open(checkpoint_file, "rb")
     ) as fp:
-        checkpoint = torch.load(fp, map_location=device)
+        checkpoint = torch.load(fp, map_location=device,weights_only=True)
     del checkpoint_file
 
     dims = ModelDimensions(**checkpoint["dims"])
@@ -157,4 +169,4 @@ def load_model(
     if alignment_heads is not None:
         model.set_alignment_heads(alignment_heads)
 
-    return model.to(device)
+    return model.to(device)
\ No newline at end of file
diff --git a/whisper/model.py b/whisper/model.py
index e53744738..997b54c3b 100644
--- a/whisper/model.py
+++ b/whisper/model.py
@@ -224,6 +224,47 @@ def __init__(
         mask = torch.empty(n_ctx, n_ctx).fill_(-np.inf).triu_(1)
         self.register_buffer("mask", mask, persistent=False)
 
+        # Optimisation: pre-compute and register the mask in CUDA if available
+        if torch.cuda.is_available():
+            self.register_buffer("mask_cuda", mask.cuda(), persistent=False)
+
+
+    def forward(self, tokens: Tensor, audio_features: Tensor) -> Tensor:
+        """
+        Args:
+            tokens: (n_batch, n_token)
+            audio_features: (n_batch, n_audio_ctx, n_audio_state)
+
+        Returns:
+            logits: (n_batch, n_token, n_vocab)
+        """
+        n_batch, n_token = tokens.shape
+        n_audio_ctx, n_audio_state = audio_features.shape[1:]
+
+        x = self.token_embedding(tokens) + self.positional_embedding[:n_token]
+
+        # Optimisation: Move audio_features to GPU once here.
+        if torch.cuda.is_available():
+            audio_features = audio_features.cuda()
+
+
+        for block in self.blocks:
+            x = block(x, audio_features)
+
+        x = self.ln(x)
+        logits = x @ self.token_embedding.weight.T
+
+        # Optimisation: Apply the precomputed CUDA mask if available.
+        if torch.cuda.is_available():
+             mask = self.mask_cuda[:n_token, :n_token]
+        else:
+            mask = self.mask[:n_token, :n_token]
+        
+        logits = logits + mask
+
+        return logits
+
+
     def forward(self, x: Tensor, xa: Tensor, kv_cache: Optional[dict] = None):
         """
         x : torch.LongTensor, shape = (batch_size, <= n_ctx)
@@ -342,4 +383,4 @@ def install_hooks(layer: nn.Module):
 
     detect_language = detect_language_function
     transcribe = transcribe_function
-    decode = decode_function
+    decode = decode_function
\ No newline at end of file