goext/langext/baseAny.go
Mike Schwörer 2fbd5cf965
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v0.0.295 added generic base-conversion algorithm
2023-11-01 00:23:17 +01:00

179 lines
2.9 KiB
Go

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
}