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: readable_size.rs
    path of file: ./repos/greptimedb/src/common/base/src
    
    the code of the file until where you have to start completion: // Copyright (c) 2017-present, PingCAP, Inc. Licensed under Apache-2.0.

// Copyright 2023 Greptime Team
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// This file is copied from https://github.com/tikv/raft-engine/blob/8dd2a39f359ff16f5295f35343f626e0c10132fa/src/util.rs

use std::fmt::{self, Debug, Display, Write};
use std::ops::{Div, Mul};
use std::str::FromStr;

use serde::de::{Unex
    
    fn from_str(s: &str) -> Result<ReadableSize, String> {
        let size_str = s.trim();
        if size_str.is_empty() {
            return Err(format!("{:?} is not a valid size.", s));
        }

        if !size_str.is_ascii() {
            return Err(format!("ASCII string is expected, but got {:?}", s));
        }

        // size: digits and '.' as decimal separator
        let size_len = size_str
            .to_string()
            .chars()
            .take_while(|c| char::is_ascii_digit(c) || ['.', 'e', 'E', '-', '+'].contains(c))
            .count();

        // unit: alphabetic characters
        let (size, unit) = size_str.split_at(size_len);

        let unit = match unit.trim() {
            "K" | "KB" | "KiB" => KIB,
            "M" | "MB" | "MiB" => MIB,
            "G" | "GB" | "GiB" => GIB,
            "T" | "TB" | "TiB" => TIB,
            "P" | "PB" | "PiB" => PIB,
            "B" | "" => B,
            _ => {
                return Err(format!(
                    "only B, KB, KiB, MB, MiB, GB, GiB, TB, TiB, PB, and PiB are supported: {:?}",
                    s
                ));
            }
        };

        match size.parse::<f64>() {
            Ok(n) => Ok(ReadableSize((n * unit as f64) as u64)),
            Err(_) => Err(format!("invalid size string: {:?}", s)),
        }
    }