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: sha256.rs
    path of file: ./repos/tock/capsules/extra/src
    
    the code of the file until where you have to start completion: // Licensed under the Apache License, Version 2.0 or the MIT License.
// SPDX-License-Identifier: Apache-2.0 OR MIT
// Copyright Tock Contributors 2022.

//! Software implementation of SHA-256.
//!
//! Implementation is based on the Wikipedia description of the
//! algorithm. It performs the hash using 32-bit native values,
//! translating the input data into the endianness of the processor
//! and translating the output into big endian format.

use core::cell::Cell;
use kernel::deferred_call::{DeferredCall, DeferredCall
    
    fn compute_buffer(&self, buffer: &[u8]) {
        // This is clearly inefficient (copy a u8 array into a u32
        // array), but it's better than using unsafe.  This
        // implementation is not intended to be high performance.
        let mut message_schedule: [u32; 64] = [0; 64];
        for i in 0..16 {
            let val: u32 = (buffer[i * 4 + 0] as u32) << 24
                | (buffer[i * 4 + 1] as u32) << 16
                | (buffer[i * 4 + 2] as u32) << 8
                | (buffer[i * 4 + 3] as u32);
            message_schedule[i] = val;
        }
        self.perform_sha(&mut message_schedule);
    }