39 lines
929 B
Go
39 lines
929 B
Go
package base58
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import (
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"errors"
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"math/big"
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)
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func DecodeBase58(value string, size int64) ([]byte, error) {
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buf := []byte(value)
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longValue := big.NewInt(0)
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result := make([]byte, size)
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for i := int64(len(buf) - 1); i >= 0; i-- {
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to_add := big.NewInt(0)
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to_add = to_add.Exp(big.NewInt(58), big.NewInt(i), to_add)
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c, err := CharacterIndex(buf[int64(len(buf))-i-1])
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if err != nil {
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return result, err
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}
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to_add = to_add.Mul(c, to_add)
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longValue = longValue.Add(to_add, longValue)
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}
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for i := size - 1; i >= 0; i-- {
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m := big.NewInt(0)
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longValue, m = longValue.DivMod(longValue, big.NewInt(256), m)
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bs := m.Bytes()
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if len(bs) == 0 {
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bs = append(bs, 0x00)
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}
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b := byte(bs[0])
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result[i] = b
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}
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if longValue.Int64() != 0 {
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return result, errors.New("cannot decode to the given size")
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}
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if size != int64(len(result)) {
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return result, errors.New("length mismatch")
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}
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return result, nil
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}
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