MD5怎么能这么快？ 加密/ MD5

I need to compute the hash (md5 is ok) for a large number of files. So, in Go I have this code:

package main

import (
    "io"
    "os"
    "fmt"
    "path/filepath"

    "crypto/md5"
    "encoding/hex"
)

func strSliceRemove(slice []string, str string) []string {
    var tempSlice []string;

    for _, item := range slice {
        if item != str {
            tempSlice = append(tempSlice, item)
        }
    }

    return tempSlice
}

func fileMD5(path string) (string, error) {
    var returnMD5String string
    file, err := os.Open(path)

    if err != nil {
        return returnMD5String, err
    }
    defer file.Close()

    hash := md5.New()

    if _, err := io.Copy(hash, file); err != nil {
        return returnMD5String, err
    }

    hashInBytes := hash.Sum(nil)[:16]
    returnMD5String = hex.EncodeToString(hashInBytes)

    return returnMD5String, nil
}

func main() {
    var doRead func(string)

    doRead = func(sd string) {
        filepath.Walk(sd, func(path string, f os.FileInfo, err error) error {
            resolvedPath, resolvedPathErr := filepath.EvalSymlinks(path)
            if resolvedPathErr != nil {
                return nil
            }

            if f.Mode()&os.ModeSymlink == os.ModeSymlink {
                doRead(resolvedPath)
            } else {
                if !f.IsDir() {
                    md5, _ := fileMD5(path)
                    fmt.Printf("%s
", md5)
                }
            }

            return nil
        })
    }

    doRead("/tmp/electron")
    return
}

It hashes correctly 1400 files in almost one second. If I use my OSX md5 command line utility, it takes more than 10 times the time. It is 10 times slower:

for FILE in `find /tmp/electron`; do
    if [ ! -d "$FILE" ]; then
        md5 $FILE;
    fi;
done;

I tried a basic c program that does the same (based on this answer How to calculate the MD5 hash of a large file in C?) and still the time seems more or less 10 seconds.

What kind of strategy / library does crypto/md5 use?