Pickle decoder fix and Long1 opcode addition. (#2824)

* Pickle decoder changes: added Long1 opcode, fixed tensor offset calculation

* Apply rustfmt.

---------

Co-authored-by: Laurent <laurent.mazare@gmail.com>

candle-core/src/pickle.rs

@@ -45,6 +45,7 @@ pub enum OpCode {
     BinFloat = b'G',
     Append = b'a',
     Appends = b'e',
+    Long1 = 0x8a,
 }
 
 // Avoid using FromPrimitive so as not to drag another dependency.
@@ -84,6 +85,7 @@ impl TryFrom<u8> for OpCode {
             b'G' => Ok(Self::BinFloat),
             b'a' => Ok(Self::Append),
             b'e' => Ok(Self::Appends),
+            0x8a => Ok(Self::Long1),
             value => Err(value),
         }
     }
@@ -106,6 +108,7 @@ pub enum Object {
         class_name: String,
     },
     Int(i32),
+    Long(i64),
     Float(f64),
     Unicode(String),
     Bool(bool),
@@ -170,6 +173,14 @@ impl Object {
         }
     }
 
+    pub fn int_or_long(self) -> OResult<i64> {
+        match self {
+            Self::Int(t) => Ok(t as i64),
+            Self::Long(t) => Ok(t),
+            _ => Err(self),
+        }
+    }
+
     pub fn tuple(self) -> OResult<Vec<Self>> {
         match self {
             Self::Tuple(t) => Ok(t),
@@ -590,6 +601,15 @@ impl Stack {
                 let obj = self.new_obj(class, args)?;
                 self.push(obj)
             }
+            OpCode::Long1 => {
+                let n_bytes = r.read_u8()?;
+                let mut v = 0;
+                // Decode the next n bytes in little endian
+                for i in 0..n_bytes {
+                    v |= (r.read_u8()? as i64) << (i * 8);
+                }
+                self.push(Object::Long(v))
+            }
         }
         Ok(false)
     }
@@ -607,10 +627,10 @@ fn rebuild_args(args: Object) -> Result<(Layout, DType, String, usize)> {
     let mut args = args.tuple()?;
     let stride = Vec::<usize>::try_from(args.remove(3))?;
     let size = Vec::<usize>::try_from(args.remove(2))?;
-    let offset = args.remove(1).int()? as usize;
+    let offset = args.remove(1).int_or_long()? as usize;
     let storage = args.remove(0).persistent_load()?;
     let mut storage = storage.tuple()?;
-    let storage_size = storage.remove(4).int()? as usize;
+    let storage_size = storage.remove(4).int_or_long()? as usize;
     let path = storage.remove(2).unicode()?;
     let (_module_name, class_name) = storage.remove(1).class()?;
     let dtype = match class_name.as_str() {
@@ -624,7 +644,11 @@ fn rebuild_args(args: Object) -> Result<(Layout, DType, String, usize)> {
             crate::bail!("unsupported storage type {other}")
         }
     };
-    let layout = Layout::new(crate::Shape::from(size), stride, offset);
+    let layout = Layout::new(
+        crate::Shape::from(size),
+        stride,
+        offset * dtype.size_in_bytes(),
+    );
     Ok((layout, dtype, path, storage_size))
 }