Port short uuid code to Go

tools/utils/short-uuid.go

@@ -0,0 +1,91 @@
+// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package utils
+
+import (
+	"math"
+	"math/big"
+
+	"github.com/ALTree/bigfloat"
+	"github.com/google/uuid"
+)
+
+const (
+	ESCAPE_CODE_SAFE_ALPHABET = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~ "
+	HUMAN_ALPHABET            = "23456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+)
+
+func num_to_string(number *big.Int, alphabet []rune, alphabet_len *big.Int, pad_to_length int) string {
+	var zero, digit big.Int
+	if number.Sign() < 0 {
+		*number = zero
+	}
+	capacity := 64
+	if pad_to_length > capacity {
+		capacity = pad_to_length
+	}
+	ans := make([]rune, 0, capacity)
+	for number.Cmp(&zero) == 1 {
+		number.DivMod(number, alphabet_len, &digit)
+		ans = append(ans, alphabet[digit.Uint64()])
+	}
+	al := len(ans)
+	if pad_to_length > -1 && al < pad_to_length {
+		ans = ans[:pad_to_length]
+		for i := al; i < pad_to_length; i++ {
+			ans[i] = alphabet[0]
+		}
+	}
+	return string(ans)
+}
+
+func get_padding_length(alphabet_len int) int {
+	bi := big.NewInt(2)
+	bi = bi.Exp(bi, big.NewInt(128), nil)
+	bb := new(big.Float).SetPrec(256)
+	bb.SetInt(bi)
+	log_al := bigfloat.Log(big.NewFloat(float64(alphabet_len)).SetPrec(256))
+	log_b := bigfloat.Log(bb)
+	res := new(big.Float).SetPrec(256)
+	res = res.Quo(log_b, log_al)
+	val, _ := res.Float64()
+	return int(math.Ceil(val))
+}
+
+type ShortUUID struct {
+	alphabet      []rune
+	alphabet_len  big.Int
+	pad_to_length int
+}
+
+func CreateShortUUID(alphabet string) *ShortUUID {
+	if alphabet == "" {
+		alphabet = HUMAN_ALPHABET
+	}
+	var ans = ShortUUID{
+		alphabet: []rune(alphabet),
+	}
+	ans.pad_to_length = get_padding_length(len(ans.alphabet))
+	ans.alphabet_len.SetUint64(uint64(len(ans.alphabet)))
+	return &ans
+}
+
+func (self *ShortUUID) Uuid4() (string, error) {
+	b, err := uuid.NewRandom()
+	if err != nil {
+		return "", err
+	}
+	bb, err := b.MarshalBinary()
+	if err != nil {
+		return "", err
+	}
+	var bi big.Int
+	bi.SetBytes(bb)
+	return num_to_string(&bi, self.alphabet, &self.alphabet_len, self.pad_to_length), nil
+}
+
+var HumanUUID *ShortUUID
+
+func init() {
+	HumanUUID = CreateShortUUID(HUMAN_ALPHABET)
+}

tools/utils/short-uuid_test.go

@@ -0,0 +1,28 @@
+// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package utils
+
+import (
+	"math/big"
+	"testing"
+)
+
+func TestShortUUID(t *testing.T) {
+	if HumanUUID.pad_to_length != 22 {
+		t.Fatalf("pad length for human UUID is %d not %d", HumanUUID.pad_to_length, 22)
+	}
+	u, err := HumanUUID.Uuid4()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(u) != 22 {
+		t.Fatalf("uuid4 %s has unexpected length: %d", u, len(u))
+	}
+
+	b := big.NewInt(int64(1234567890123456789))
+	q := num_to_string(b, HumanUUID.alphabet, &HumanUUID.alphabet_len, HumanUUID.pad_to_length)
+	const expected = "bzT6LtUjw4422222222222"
+	if q != expected {
+		t.Fatalf("unexpected short human serialization: %s != %s", q, expected)
+	}
+}