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adler32 is not nearly unique. switching to sh256 and adding tests

This commit is contained in:
Vincent Batts 2013-11-05 11:34:16 -05:00
parent 2a87e1f8ca
commit 629bafaa7f
2 changed files with 21 additions and 4 deletions

View file

@ -2,13 +2,18 @@ package hash
import (
"crypto/md5"
"crypto/sha256"
"fmt"
"hash/adler32"
"io"
"math/rand"
"strings"
"time"
)
func init() {
rand.Seed(time.Now().UnixNano())
}
func Rand64() int64 {
return rand.Int63()
}
@ -31,7 +36,7 @@ func GetMd5FromBytes(blob []byte) (sum []byte) {
/* get a small, decently unique hash */
func GetSmallHash() (small_hash string) {
h := adler32.New()
io.WriteString(h, fmt.Sprintf("%d", time.Now().Unix()))
return fmt.Sprintf("%X", h.Sum(nil))
h := sha256.New()
io.WriteString(h, fmt.Sprintf("%d%d", time.Now().UnixNano(), Rand64()))
return strings.ToLower(fmt.Sprintf("%X", h.Sum(nil)[0:9]))
}

View file

@ -3,6 +3,7 @@ package hash
import (
"fmt"
"testing"
"sort"
)
func TestRand64(t *testing.T) {
@ -36,4 +37,15 @@ func TestMd5String(t *testing.T) {
}
func TestHash(t *testing.T) {
seen := []string{}
for i := 0; i < 10000; i++ {
h := GetSmallHash()
j := sort.SearchStrings(seen, h)
if len(seen) != 0 && j < len(seen) && h == seen[j] {
t.Errorf("there is a non-unique hash after %d attempts [%s and %s]", i, h, seen[j])
} else {
seen = append(seen, h)
sort.Strings(seen)
}
}
}