v0.0.295 added generic base-conversion algorithm

langext/baseAny.go

@@ -0,0 +1,178 @@
+package langext
+
+import (
+	"crypto/rand"
+	"errors"
+	"math"
+	"math/big"
+)
+
+type AnyBaseConverter struct {
+	base    uint64
+	charset []rune
+}
+
+func NewAnyBaseConverter(cs string) AnyBaseConverter {
+	rcs := []rune(cs)
+	return AnyBaseConverter{
+		base:    uint64(len(rcs)),
+		charset: rcs,
+	}
+}
+
+func (bc AnyBaseConverter) Rand(rlen int) string {
+	biBase := big.NewInt(int64(bc.base))
+
+	randMax := big.NewInt(math.MaxInt64)
+
+	r := ""
+
+	for i := 0; i < rlen; i++ {
+		v, err := rand.Int(rand.Reader, randMax)
+		if err != nil {
+			panic(err)
+		}
+
+		r += string(bc.charset[v.Mod(v, biBase).Int64()])
+	}
+
+	return r
+}
+
+func (bc AnyBaseConverter) EncodeUInt64(num uint64) string {
+	if num == 0 {
+		return "0"
+	}
+
+	b := ""
+
+	// loop as long the num is bigger than zero
+	for num > 0 {
+		r := num % bc.base
+
+		num -= r
+		num /= base62Base
+
+		b += string(bc.charset[int(r)])
+	}
+
+	return b
+}
+
+func (bc AnyBaseConverter) DecodeUInt64(str string) (uint64, error) {
+	if str == "" {
+		return 0, errors.New("empty string")
+	}
+
+	result := uint64(0)
+
+	for _, v := range str {
+		result *= base62Base
+
+		pos := ArrFirstIndex(bc.charset, v)
+		if pos == -1 {
+			return 0, errors.New("invalid character: " + string(v))
+		}
+
+		result += uint64(pos)
+	}
+
+	return result, nil
+}
+
+func (bc AnyBaseConverter) Encode(src []byte) string {
+	value := new(big.Int)
+	value.SetBytes(src)
+	return bc.EncodeBigInt(value)
+}
+
+func (bc AnyBaseConverter) EncodeBigInt(src *big.Int) string {
+	value := new(big.Int)
+	value.Set(src)
+
+	isneg := value.Sign() < 0
+
+	answer := ""
+
+	if isneg {
+		value.Neg(value)
+	}
+
+	biBase := big.NewInt(int64(bc.base))
+
+	rem := new(big.Int)
+
+	for value.Sign() > 0 {
+		value.QuoRem(value, biBase, rem)
+		answer = string(bc.charset[rem.Int64()]) + answer
+	}
+
+	if isneg {
+		return "-" + answer
+	} else {
+		return answer
+	}
+}
+
+func (bc AnyBaseConverter) Decode(src string) ([]byte, error) {
+	value, err := bc.DecodeToBigInt(src)
+	if err != nil {
+		return nil, err
+	}
+	return value.Bytes(), nil
+}
+
+func (bc AnyBaseConverter) DecodeToBigInt(_src string) (*big.Int, error) {
+	result := new(big.Int)
+	result.SetInt64(0)
+
+	src := []rune(_src)
+
+	if len(src) == 0 {
+		return nil, errors.New("string is empty")
+	}
+	if bc.base < 2 {
+		return nil, errors.New("not enough digits")
+	}
+
+	i := 0
+
+	sign := new(big.Int)
+	sign.SetInt64(1)
+	if src[i] == '+' {
+		i++
+	} else if src[i] == '-' {
+		i++
+		sign.SetInt64(-1)
+	}
+
+	if i >= len(src) {
+		return nil, errors.New("no digits in input")
+	}
+
+	biBase := big.NewInt(int64(bc.base))
+
+	oldResult := new(big.Int)
+
+	for ; i < len(src); i++ {
+		n := ArrFirstIndex(bc.charset, src[i])
+		if n < 0 {
+			return nil, errors.New("invalid characters in input")
+		}
+
+		oldResult.Set(result)
+
+		result.Mul(result, biBase)
+		result.Add(result, big.NewInt(int64(n)))
+
+		if result.Cmp(oldResult) < 0 {
+			return nil, errors.New("overflow")
+		}
+	}
+
+	if sign.Cmp(big.NewInt(0)) < 0 {
+		result.Neg(result)
+	}
+
+	return result, nil
+}