You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: scale_encoding.rs
    path of file: ./repos/solang/src/codegen/encoding
    
    the code of the file until where you have to start completion: // SPDX-License-Identifier: Apache-2.0

use crate::codegen::cfg::{ControlFlowGraph, Instr};
use crate::codegen::encoding::AbiEncoding;
use crate::codegen::vartable::Vartable;
use crate::codegen::{Builtin, Expression};
use crate::sema::ast::StructType;
use crate::sema::ast::{Namespace, Type, Type::Uint};
use parity_scale_codec::Encode;
use primitive_types::U256;
use solang_parser::pt::Loc::Codegen;
use std::collections::HashMap;

use super::buffer_validator::BufferValidator;

pub(super) struct ScaleEncoding {
    storage_cache: HashMap<usize, Expression>,
    packed_encoder: bool,
}

impl ScaleEncoding {
    pub fn new(packed: bool) -> Self {
        Self {
            storage_cache: HashMap::new(),
            packed_encoder: packed,
        }
    }
}

/// Decoding the compact integer at current `offset` inside `buffer`.
/// Returns the variable number of the decoded integer (32bit) and the width in bytes of the encoded version.
/// More information can found in the /// [SCALE documentation](https://docs.substrate.io/reference/scale-codec/).
fn decode_compact(
    buffer: &Expression,
    offset: &Expression,
    vartab: &mut Vartable,
    cfg: &mut ControlFlowGraph,
) -> (usize, Expression) {
    let decoded_var = vartab.
    
    fn const_encode(&self, args: &[Expression]) -> Option<Vec<u8>> {
        let mut result = vec![];
        for arg in args {
            match arg {
                Expression::AllocDynamicBytes {
                    initializer: Some(data),
                    ty: Type::String | Type::DynamicBytes,
                    ..
                } => result.extend_from_slice(&data.encode()),
                Expression::AllocDynamicBytes {
                    initializer: Some(data),
                    ty: Type::Slice(inner),
                    ..
                } if matches!(**inner, Type::Bytes(1)) => result.extend_from_slice(data),
                Expression::NumberLiteral {
                    ty: Type::Bytes(4),
                    value,
                    ..
                } => {
                    let bytes = value.to_bytes_be().1;
                    if bytes.len() < 4 {
                        let buf = vec![0; 4 - bytes.len()];
                        result.extend_from_slice(&buf);
                    }
                    result.extend_from_slice(&bytes[..]);
                }
                Expression::NumberLiteral {
                    ty: Type::Uint(256),
                    value,
                    ..
                } => {
                    let bytes = value.to_bytes_be().1;
                    result.extend_from_slice(&U256::from_big_endian(&bytes).encode()[..]);
                }
                _ => return None,
            }
        }
        result.into()
    }