I need to make smaller commits

src/bytecode.rs

@@ -58,6 +58,7 @@ impl Bytecode {
             0x57 => (Instruction::Pop(), 1),
             0x59 => (Instruction::Duplicate(), 1),
 
+            0x60 => (Instruction::AddInt(), 1),
             0x68 => (Instruction::MultiplyInt(), 1),
             0x6C => (Instruction::DivideInt(), 1),
             0x6D => (Instruction::DivideLong(), 1),
@@ -80,7 +81,7 @@ impl Bytecode {
             }
             0x9C => {
                 let bytes = [self.bytes[offset+1], self.bytes[offset+2]];
-                (Instruction::BranchNonPositive(i16::from_be_bytes(bytes)), 3)
+                (Instruction::BranchNonNegative(i16::from_be_bytes(bytes)), 3)
             }
             0x9D => {
                 let bytes = [self.bytes[offset+1], self.bytes[offset+2]];
@@ -88,7 +89,7 @@ impl Bytecode {
             }
             0x9E => {
                 let bytes = [self.bytes[offset+1], self.bytes[offset+2]];
-                (Instruction::BranchNonNegative(i16::from_be_bytes(bytes)), 3)
+                (Instruction::BranchNonPositive(i16::from_be_bytes(bytes)), 3)
             }
 
             0x9F => {
@@ -227,6 +228,7 @@ pub enum Instruction {
     Pop()                       = 0x57, // Pop top stack value
     Duplicate()                 = 0x59, // duplicate top stack value
 
+    AddInt()                    = 0x60, // int addition
     MultiplyInt()               = 0x68, // int multiplication
     DivideInt()                 = 0x6C, // integer division, round toward zero and more rules
     DivideLong()                = 0x6D, // long division
@@ -238,9 +240,9 @@ pub enum Instruction {
     BranchZero(i16)             = 0x99, // branch if value == 0
     BranchNonZero(i16)          = 0x9A, // branch if value != 0
     BranchNegative(i16)         = 0x9B, // branch if value <  0
-    BranchNonPositive(i16)      = 0x9C, // branch if value <= 0
+    BranchNonNegative(i16)      = 0x9C, // branch if value <= 0
     BranchPositive(i16)         = 0x9D, // branch if value >  0
-    BranchNonNegative(i16)      = 0x9E, // branch if value >= 0
+    BranchNonPositive(i16)      = 0x9E, // branch if value >= 0
 
     BranchIntEquality(i16)      = 0x9F,
     BranchIntInequality(i16)    = 0xA0,

src/classfile.rs

@@ -5,7 +5,7 @@ use core::str::Utf8Error;
 
 use crate::accessmasks::*;
 use crate::bytecode::Bytecode;
-use crate::constantpool::{ ConstantFieldRefInfo, ConstantPoolInfo, ConstantUtf8Info, ConstantStringInfo, ConstantMethodRefInfo, ConstantClassInfo, ConstantNameAndTypeInfo, ConstantIntegerInfo, ConstantLongInfo  };
+use crate::constantpool::{ ConstantFieldRefInfo, ConstantPoolInfo, ConstantUtf8Info, ConstantStringInfo, ConstantMethodRefInfo, ConstantFloatInfo, ConstantClassInfo, ConstantNameAndTypeInfo, ConstantIntegerInfo, ConstantLongInfo  };
 
 #[derive(Debug)]
 pub enum Error {
@@ -246,6 +246,15 @@ impl JavaClassFile {
         };
     }
 
+    pub fn pool_float_entry(&self, index: u16) -> Result<&ConstantFloatInfo, Error> {
+        let pool_entry = self.pool_entry(index)?;
+
+        return match pool_entry {
+            ConstantPoolInfo::Float(data) => Ok(data),
+            _ => Err(Error::BadFileError(format!("Expected constant pool entry {} in class {} to be of type Float but found {:?}", index, self.get_classname()?, pool_entry)))
+        };
+    }
+
     pub fn pool_long_entry(&self, index: u16) -> Result<&ConstantLongInfo, Error> {
         let pool_entry = self.pool_entry(index)?;
 
@@ -282,6 +291,12 @@ impl JavaClassFile {
         };
     }
 
+    pub fn gather_float(&self, index: u16) -> Result<f32, Error> {
+        let float = self.pool_float_entry(index)?;
+
+        return Ok(float.value);
+    }
+
     pub fn gather_string(&self, index: u16) -> Result<&String, Error> {
         let string = self.pool_string_entry(index)?;
 
@@ -775,8 +790,8 @@ impl From<&str> for AbstractTypeKind {
               'J' =>    AbstractTypeKind::Long(),
               'S' =>    AbstractTypeKind::Short(),
               'Z' =>    AbstractTypeKind::Boolean(),
-              'L' => todo!(),
-              _ => todo!(),
+              'L' =>    AbstractTypeKind::Classname(value.chars().skip(1).map_while(|c| if c != ';' { Some(c) } else { None } ).collect()),
+              _ => unreachable!(),
         }
     }
 }

src/classstore.rs

@@ -12,24 +12,24 @@ use crate::iterators::CompatibleTypesIterator;
 
 #[derive(Debug)]
 pub struct ClassStore {
-    class_ids: HashMap<String, usize>,
-    array_classes: HashMap<AbstractTypeDescription, ObjectReference>,
-    classes: Vec<ClassStoreEntry>,
-    class_path_fragments: Vec<PathBuf>,
-    native_class_names: Vec<String>,
-    primitive_classes: PrimitiveClassStore,
+    pub class_ids: HashMap<String, usize>,
+    pub array_classes: HashMap<AbstractTypeDescription, ObjectReference>,
+    pub classes: Vec<ClassStoreEntry>,
+    pub class_path_fragments: Vec<PathBuf>,
+    pub native_class_names: Vec<String>,
+    pub primitive_classes: PrimitiveClassStore,
 }
 
 #[derive(Debug, Default)]
 pub struct PrimitiveClassStore {
-    byte_class: ObjectReference,
-    char_class: ObjectReference, 
-    double_class: ObjectReference,
-    float_class: ObjectReference,
-    integer_class: ObjectReference,
-    long_class: ObjectReference,
-    short_class: ObjectReference,
-    boolean_class: ObjectReference,
+    pub byte_class: ObjectReference,
+    pub char_class: ObjectReference, 
+    pub double_class: ObjectReference,
+    pub float_class: ObjectReference,
+    pub int_class: ObjectReference,
+    pub long_class: ObjectReference,
+    pub short_class: ObjectReference,
+    pub boolean_class: ObjectReference,
 }
 
 #[derive(Debug)]
@@ -228,6 +228,27 @@ impl ClassStore {
             AbstractTypeKind::Boolean() => {
                 Some(self.primitive_classes.boolean_class)
             }
+            AbstractTypeKind::Byte() => {
+                Some(self.primitive_classes.byte_class)
+            }
+            AbstractTypeKind::Char() => {
+                Some(self.primitive_classes.char_class)
+            }
+            AbstractTypeKind::Double() => {
+                Some(self.primitive_classes.double_class)
+            }
+            AbstractTypeKind::Float() => {
+                Some(self.primitive_classes.float_class)
+            }
+            AbstractTypeKind::Int() => {
+                Some(self.primitive_classes.int_class)
+            }
+            AbstractTypeKind::Long() => {
+                Some(self.primitive_classes.long_class)
+            }
+            AbstractTypeKind::Short() => {
+                Some(self.primitive_classes.short_class)
+            }
             _ => todo!(),
         }
     }

src/iterators.rs

@@ -104,7 +104,7 @@ impl <'i>ClassMethodIterator<'i> {
     }
 }
 
-impl <'i> Iterator for ClassMethodIterator<'i>{
+impl <'i> Iterator for ClassMethodIterator<'i> {
     type Item = (usize, usize, &'i MethodInfo); // class index, method index, method info
 
     fn next(&mut self) -> Option<Self::Item> {

src/jvm.rs

@@ -13,8 +13,8 @@ use crate::constantpool::{ ConstantPoolInfo, ConstantClassInfo, ConstantUtf8Info
 use crate::heap_area::{ HeapArea, FieldValue, ObjectReference, CompartmentEntry };
 use crate::iterators::{ ClassMethodIterator, ClassFieldIterator };
 use crate::native_methods;
-use crate::native_methods::ignore_call;
-use crate::native_registry::{ NativeRegistry };
+use crate::native_methods::{ EntryPoint, ignore_call };
+use crate::native_registry::NativeRegistry;
 use crate::stackframe;
 use crate::stackframe::{ StackFrame, StackValue, OperandStack };
 
@@ -233,10 +233,6 @@ impl JVM {
         primitive_class_object
     }
 
-    fn register_native(&mut self, class_name: &str, method_name: &str, method_descriptor: &MethodDescriptor) {
-        self.native_registry.register("java/lang/System", "registerNatives", ignore_call);
-    }
-
     pub fn entrypoint(&mut self, class_name: &String, method_name: &String, arguments: &[&str]) -> Result<(), Error> {
         let entry_class = JavaClassFile {
             minor_version: 0,
@@ -251,12 +247,17 @@ impl JVM {
                     ConstantPoolInfo::Utf8(ConstantUtf8Info { utf8: class_name.to_string() }),
                     ConstantPoolInfo::Utf8(ConstantUtf8Info { utf8: method_name.to_string() }),
                     ConstantPoolInfo::Utf8(ConstantUtf8Info { utf8: "([Ljava/lang/String;)V".to_string() }),
-                    ConstantPoolInfo::MethodRef(ConstantMethodRefInfo { class_index: 11, name_and_type_index: 13}), // 10
-                    ConstantPoolInfo::Class(ConstantClassInfo { name_index: 12 } ),
-                    ConstantPoolInfo::Utf8(ConstantUtf8Info { utf8: "java/lang/String".to_string() }),
-                    ConstantPoolInfo::NameAndType(ConstantNameAndTypeInfo { name_index: 14, descriptor_index: 15 }),
-                    ConstantPoolInfo::Utf8(ConstantUtf8Info { utf8: "<init>".to_string() }),
-                    ConstantPoolInfo::Utf8(ConstantUtf8Info { utf8: "([B)V".to_string() }), // 15
+                    ConstantPoolInfo::MethodRef(ConstantMethodRefInfo { class_index: 1, name_and_type_index: 11}), // 10
+                    ConstantPoolInfo::NameAndType(ConstantNameAndTypeInfo { name_index: 12, descriptor_index: 13 }),
+                    ConstantPoolInfo::Utf8(ConstantUtf8Info { utf8: "populateUnsafeConstants".to_string() }),
+                    ConstantPoolInfo::Utf8(ConstantUtf8Info { utf8: "()V".to_string() }),
+                    ConstantPoolInfo::Class(ConstantClassInfo { name_index: 15 }),
+                    ConstantPoolInfo::Utf8(ConstantUtf8Info { utf8: "jdk/internal/misc/UnsafeConstants".to_string() }), // 15
+                    ConstantPoolInfo::MethodRef(ConstantMethodRefInfo { class_index: 17, name_and_type_index: 19}),
+                    ConstantPoolInfo::Class(ConstantClassInfo { name_index: 18 }),
+                    ConstantPoolInfo::Utf8(ConstantUtf8Info { utf8: "java/lang/System".to_string() }),
+                    ConstantPoolInfo::NameAndType(ConstantNameAndTypeInfo { name_index: 20, descriptor_index: 13 }),
+                    ConstantPoolInfo::Utf8(ConstantUtf8Info { utf8: "initPhase1".to_string() }),
                 ]
             ),
             access_flags: ClassAccessFlagMask { mask: ClassAccessFlag::Super.discriminant() },
@@ -267,7 +268,7 @@ impl JVM {
             methods: Box::new([
                 MethodInfo {
                     access_flags: MethodAccessFlagMask { 
-                        mask: MethodAccessFlag::Public.discriminant() | MethodAccessFlag::Static.discriminant()
+                        mask: MethodAccessFlag::Private.discriminant() | MethodAccessFlag::Static.discriminant()
                     },
                     name: "call_main".to_string(),
                     descriptor: MethodDescriptor {
@@ -287,8 +288,22 @@ impl JVM {
                                     max_locals: 1,
                                     code: Bytecode {
                                         bytes: Box::new([
-                                            0x2A_u8.to_be(), // aload_0
+                                           // access something from UnsafeConstants
+                                            0x12_u8.to_be(), // ldc
+                                            0x0E_u8.to_be(), // index 14 into the constant pool
+                                            0x57_u8.to_be(), // pop
 
+                                            // Update UnsafeConstants to actual values
+                                            0xb8_u8.to_be(), // invokestatic
+                                            0x0A_u16.to_be_bytes()[0], // index 10 into the constant
+                                            0x0A_u16.to_be_bytes()[1], // pool                      
+
+                                            // call initPhase1
+                                            0xb8_u8.to_be(), // invokestatic
+                                            0x10_u16.to_be_bytes()[0], // index 10 into the constant
+                                            0x10_u16.to_be_bytes()[1], // pool                      
+
+                                            0x2A_u8.to_be(), // aload_0
                                             0xB8_u8.to_be(), // invokestatic
                                             0x04_u16.to_be_bytes()[0], // index 4 into the constant
                                             0x04_u16.to_be_bytes()[1], // pool                      
@@ -301,29 +316,47 @@ impl JVM {
                         }
                     ])
                 },
+                MethodInfo {
+                    access_flags: MethodAccessFlagMask { 
+                        mask: MethodAccessFlag::Private.discriminant() | MethodAccessFlag::Static.discriminant() | MethodAccessFlag::Native.discriminant()
+                    },
+                    name: "populateUnsafeConstants".to_string(),
+                    descriptor: MethodDescriptor {
+                        argument_types: Box::new([]),
+                        return_type: AbstractTypeDescription {
+                            array_level: 0,
+                            kind: AbstractTypeKind::Void(),
+                        }
+                    },
+                    code_attribute_index: 0,
+                    attributes: Box::new([])
+                }
             ]),
             attributes: Box::new([]),
         };
 
+        self.native_registry.register("::EntryPoint", "populateUnsafeConstants", EntryPoint::populate_unsafe_constants);
+
         self.class_store.add_class(entry_class, true)?;                              // 0
         self.class_store.add_class(JVM::class_native_class_data(), true)?;           // 1
         self.load_class(&"java/lang/Object".to_string())?;                           // 2
         self.load_class(&"java/lang/Number".to_string())?;                           // 3
-        self.load_class(&"java/lang/Byte".to_string())?;            // 4
-        self.load_class(&"java/lang/String".to_string())?;          // 5
-        self.load_class(&"java/lang/Class".to_string())?;           // 6
+        let byte_class_index = self.load_class(&"java/lang/Byte".to_string())?;      // 4
+        let string_class_index = self.load_class(&"java/lang/String".to_string())?;  // 5
+        let class_class_index = self.load_class(&"java/lang/Class".to_string())?;    // 6
+        let system_class_index = self.load_class(&"java/lang/System".to_string())?;  // 7
 
         self.make_class_class("Ljava/lang/Byte;");
         self.make_class_class("Ljava/lang/String;");
         self.make_array_class(
-            self.class_store.get_class_objectref_from_index(4),
+            self.class_store.get_class_objectref_from_index(byte_class_index),
             AbstractTypeDescription {
                 array_level: 0,
                 kind: AbstractTypeKind::Classname("java/lang/Byte".into()),
             }
         );
         self.make_array_class(
-            self.class_store.get_class_objectref_from_index(5),
+            self.class_store.get_class_objectref_from_index(string_class_index),
             AbstractTypeDescription {
                 array_level: 0,
                 kind: AbstractTypeKind::Classname("java/lang/String".into()),
@@ -332,18 +365,24 @@ impl JVM {
 
         self.heap_area.fill_byte_cache(&self.class_store);
 
-        let int_class_ref = self.make_primitive_class("int", "I");
-        let byte_class_ref = self.make_primitive_class("byte", "B");
+        self.class_store.primitive_classes.int_class     = self.make_primitive_class("int", "I");
+        self.class_store.primitive_classes.byte_class    = self.make_primitive_class("byte", "B");
+        self.class_store.primitive_classes.char_class    = self.make_primitive_class("char", "C");
+        self.class_store.primitive_classes.long_class    = self.make_primitive_class("long", "J");
+        self.class_store.primitive_classes.float_class   = self.make_primitive_class("float", "F");
+        self.class_store.primitive_classes.short_class   = self.make_primitive_class("short", "S");
+        self.class_store.primitive_classes.double_class  = self.make_primitive_class("double", "D");
+        self.class_store.primitive_classes.boolean_class = self.make_primitive_class("boolean", "Z");
 
         self.make_array_class(
-            int_class_ref,
+            self.class_store.primitive_classes.int_class,
             AbstractTypeDescription {
                 array_level: 0,
                 kind: AbstractTypeKind::Int(),
             }
         );
         self.make_array_class(
-            byte_class_ref,
+            self.class_store.primitive_classes.byte_class,
             AbstractTypeDescription {
                 array_level: 0,
                 kind: AbstractTypeKind::Byte(),
@@ -366,7 +405,6 @@ impl JVM {
 
     pub fn run(&mut self) -> Result<(), Error> {
         while self.stack_frames.len() != 0 {
-            println!("Enter bytecode loop:");
 
             let jvm_op = self.bytecode_loop()?;
             match jvm_op {
@@ -517,6 +555,11 @@ impl JVM {
 
                                 FieldValue::Long(long_entry.value)
                             },
+                            AbstractTypeKind::Float() => {
+                                let float_entry = class_file.pool_float_entry(constant_value_info.constant_value_index)?;
+
+                                FieldValue::Float(float_entry.value)
+                            },
                             AbstractTypeKind::Classname(ref name) => {
                                 if name == "java/lang/String" {
                                     let string_entry = class_file.gather_string(constant_value_info.constant_value_index)?;
@@ -585,15 +628,15 @@ impl JVM {
     }
 
     fn bytecode_loop(&mut self) -> Result<JVMCallbackOperation, Error> {
+        //println!("Enter bytecode loop:");
 
-        let frame     = {
         let frame_index = self.stack_frames.len() - 1;
-            &mut self.stack_frames[frame_index]
-        };
+        let frame     = &mut self.stack_frames[frame_index];
         let class     =      self.class_store.class_file_from_idx(frame.class_index).unwrap();
         let method    = &    class.methods[frame.method_index as usize];
 
         if method.access_flags & MethodAccessFlag::Native {
+            println!("{:25}.{:15}:          (native)", class.get_classname().unwrap(), method.name);
             return self.native_call()
         }
 
@@ -604,10 +647,17 @@ impl JVM {
             let (instruction, offset) = bytecode.next_instruction(frame.instruction_pointer as usize);
             frame.instruction_pointer += offset as u32;
 
-            println!("{:25}.{:15}:{:<10}{instruction:?}", class.get_classname().unwrap(), method.name, frame.instruction_pointer);
+            println!("{}{:25}.{:15}:{:<10}{instruction:?}", "    ".repeat(frame_index), class.get_classname().unwrap(), method.name, frame.instruction_pointer);
 
             match instruction {
 
+                Instruction::AddInt() => {
+                    let value_0 = wrap_stackframe_error(class, method, frame.operand_stack.pop_int(0))?;
+                    let value_1 = wrap_stackframe_error(class, method, frame.operand_stack.pop_int(0))?;
+
+                    wrap_stackframe_error(class, method, frame.operand_stack.push(StackValue::Int(value_0 + value_1)))?;
+                }
+
                 Instruction::ArrayLength() => {
                     let array_reference = wrap_stackframe_error(class, method, frame.operand_stack.pop_reference(0))?;
 
@@ -659,6 +709,24 @@ impl JVM {
                     }
                 }
 
+                Instruction::BranchNonNegative(branch_offset) => {
+                    let test_value = wrap_stackframe_error(class, method, frame.operand_stack.pop_int(0))?;
+
+                    if test_value >= 0 {
+                        frame.instruction_pointer -= offset as u32;
+                        frame.instruction_pointer = if branch_offset < 0 { frame.instruction_pointer - branch_offset.abs() as u32} else { frame.instruction_pointer + branch_offset.abs() as u32};
+                    }
+                }
+
+                Instruction::BranchNonZero(branch_offset) => {
+                    let test_value = wrap_stackframe_error(class, method, frame.operand_stack.pop_int(0))?;
+
+                    if test_value != 0 {
+                        frame.instruction_pointer -= offset as u32;
+                        frame.instruction_pointer = if branch_offset < 0 { frame.instruction_pointer - branch_offset.abs() as u32} else { frame.instruction_pointer + branch_offset.abs() as u32};
+                    }
+                }
+
                 Instruction::BranchNull(branch_offset) => {
                     let test_value = wrap_stackframe_error(class, method, frame.operand_stack.pop_reference(0))?;
 
@@ -840,9 +908,6 @@ impl JVM {
                                     )));
                     }
 
-                    if callee_method_info.access_flags & MethodAccessFlag::Native {
-                    }
-
                     let supplied_descriptor: MethodDescriptor = supplied_descriptor_string.try_into()?;
                     // TODO: Throw exception on fail
 
@@ -982,6 +1047,12 @@ impl JVM {
 
                             wrap_stackframe_error(class, method, frame.operand_stack.push(StackValue::Reference(string_obj_ref)))?;
                         },
+                        ConstantPoolInfo::Float(_) => {
+                            // TODO: Handle error instead of unwrap
+                            let float_constant = class.gather_float(index as u16).unwrap();
+
+                            wrap_stackframe_error(class, method, frame.operand_stack.push(StackValue::Float(float_constant)))?;
+                        },
                         _ => {
                             println!("{:?}", class.pool_entry(index as u16).unwrap());
                             todo!()
@@ -1000,11 +1071,7 @@ impl JVM {
                                 let array_level = class_name.len() - component_name.len();
                                 let array_type_desc = AbstractTypeDescription {
                                     array_level: array_level as u8,
-                                    kind: if component_name.len() == 1 {
-                                        component_name.into()
-                                    } else {
-                                        AbstractTypeKind::Classname(component_name.to_string())
-                                    }
+                                    kind: component_name.into(),
                                 };
 
                                 if let Some(array_ref) = self.class_store.get_array_class_ref(&array_type_desc) {
@@ -1166,6 +1233,10 @@ impl JVM {
                     wrap_stackframe_error(class, method, frame.operand_stack.push(StackValue::Reference(new_object)))?;
                 },
 
+                Instruction::Pop() => {
+                    wrap_stackframe_error(class, method, frame.operand_stack.pop_computational_1(0))?;
+                }
+
                 Instruction::PushConstInt0() => {
                     wrap_stackframe_error(class, method, frame.operand_stack.push(StackValue::Int(0)))?;
                 }
@@ -1189,6 +1260,26 @@ impl JVM {
                     wrap_stackframe_error(class, method, frame.operand_stack.push(StackValue::Reference(ObjectReference::NULL)))?;
                 }
 
+                Instruction::PutField(fieldref_index) => {
+                    let (_target_class_name, target_field_name, expected_field_descriptor) = class.gather_fieldref(fieldref_index)?;
+
+                    let value = match expected_field_descriptor.as_str() {
+                        "J" | "D" => wrap_stackframe_error(class, method, frame.operand_stack.pop_computational_2(0))?,
+                        _ => match wrap_stackframe_error(class, method, frame.operand_stack.pop_computational_1(0))? {
+                            StackValue::Int(i) => FieldValue::Int(i),
+                            StackValue::Reference(r) => FieldValue::Reference(r),
+                            stack_value @ _ => {
+                                println!("{stack_value:?}");
+                                todo!()
+                            }
+                        }
+                    };
+
+                    let this_object = wrap_stackframe_error(class, method, frame.operand_stack.pop_reference(0))?;
+
+                    self.heap_area.object_area.set_object_field(this_object, target_field_name, value, frame.class_index, &self.class_store)?;
+                }
+
                 Instruction::PutStatic(fieldref_index) => {
                     let (target_class_name, target_field_name, expected_field_descriptor) = class.gather_fieldref(fieldref_index)?;
 
@@ -1228,7 +1319,13 @@ impl JVM {
                             let int_value = wrap_stackframe_error(class, method, frame.operand_stack.pop_int(0))?;
 
                             FieldValue::Boolean((int_value & 1) != 0)
-                        },
+                        }
+
+                        (0, AbstractTypeKind::Int()) => {
+                            let int_value = wrap_stackframe_error(class, method, frame.operand_stack.pop_int(0))?;
+
+                            FieldValue::Int(int_value)
+                        }
 
                         (0..=255, AbstractTypeKind::Classname(_field_type_name)) => {
                             let ref_value = wrap_stackframe_error(class, method, frame.operand_stack.pop_reference(0))?;
@@ -1404,7 +1501,8 @@ fn load_local_int(class: &JavaClassFile, method: &MethodInfo, frame: &mut StackF
 }
 
 fn fill_arguments(class: &JavaClassFile, method: &MethodInfo, arguments: &mut VecDeque<StackValue>, argument_types: &Box<[AbstractTypeDescription]>, stack: &mut OperandStack) -> Result<(), Error> {
-    for argument_type in argument_types {
+    for argument_type_index in 0..argument_types.len() {
+        let argument_type = &argument_types[argument_types.len() - argument_type_index - 1];
         if argument_type.array_level != 0 {
             // TODO: Type checking
             arguments.push_front(
@@ -1540,7 +1638,7 @@ fn fill_arguments(class: &JavaClassFile, method: &MethodInfo, arguments: &mut Ve
     Ok(())
 }
 
-fn wrap_stackframe_error<T>(class: &JavaClassFile, method: &MethodInfo, frame_result: Result<T, stackframe::Error>) -> Result<T, Error> {
+pub fn wrap_stackframe_error<T>(class: &JavaClassFile, method: &MethodInfo, frame_result: Result<T, stackframe::Error>) -> Result<T, Error> {
     match frame_result {
         Ok(t) => Ok(t),
         Err(err) => return Err(Error::StackFrameError(err, format!("in '{}', in class '{}'", method.name, class.get_classname().unwrap()))),

src/native_registry.rs

@@ -1,4 +1,5 @@
 
+use crate::stackframe::StackFrame;
 use crate::jvm::Error;
 use crate::jvm::JVMCallbackOperation;
 use crate::jvm::JVM;

src/stackframe.rs

@@ -75,6 +75,32 @@ impl OperandStack {
         }
     }
 
+    pub fn pop_computational_2(&mut self, index: usize) -> Result<FieldValue, Error> {
+        let absolute_index = self.depth as usize - 1 - index;
+        let value_top = self.stack[absolute_index];
+        let value_bot = self.stack[absolute_index - 1];
+
+        self.depth -= 2;
+
+        match (value_bot, value_top) {
+            (StackValue::Long0(l0), StackValue::Long1(l1)) => {
+                let l0_bytes = l0.to_ne_bytes();
+                let l1_bytes = l1.to_ne_bytes();
+                let concat_bytes = [l0_bytes[0], l0_bytes[1], l0_bytes[2], l0_bytes[3], l1_bytes[0], l1_bytes[1], l1_bytes[2], l1_bytes[3]];
+
+                Ok(FieldValue::Long(i64::from_ne_bytes(concat_bytes)))
+            }
+            (StackValue::Double0(d0), StackValue::Double1(d1)) => {
+                let d0_bytes = d0.to_ne_bytes();
+                let d1_bytes = d1.to_ne_bytes();
+                let concat_bytes = [d0_bytes[0], d0_bytes[1], d0_bytes[2], d0_bytes[3], d1_bytes[0], d1_bytes[1], d1_bytes[2], d1_bytes[3]];
+
+                Ok(FieldValue::Double(f64::from_ne_bytes(concat_bytes)))
+            }
+            _ => Err(Error::LocalError(format!("Mismatched type at index {index} of the function operand stack, expected type with computational type 2 but found '{value_bot:?}, {value_top:?}'")))
+        }
+    }
+    
     pub fn pop_computational_1(&mut self, index: usize) -> Result<StackValue, Error> {
         let absolute_index = self.depth as usize - 1 - index;
         let value = self.stack[absolute_index];