39 lines
709 B
Go
39 lines
709 B
Go
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package lib
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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 SqrtRepetend(x *big.Int) ([]*big.Int, error) {
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m := big.NewInt(0)
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d := big.NewInt(1)
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a0 := new(big.Int).Sqrt(x)
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s := new(big.Int).Exp(a0, big.NewInt(2), nil)
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if x.Cmp(s) == 0 {
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return nil, errors.New("input is a perfect square")
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}
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repetend := make([]*big.Int, 0)
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a := new(big.Int).Set(a0)
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twoa0 := new(big.Int).Mul(big.NewInt(2), a0)
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for a.Cmp(twoa0) != 0 {
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// m = d * a - m
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tmp := new(big.Int)
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m.Sub(tmp.Mul(d, a), m)
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// d = (x - m^2) // d
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tmp.Exp(m, big.NewInt(2), nil)
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d.Div(tmp.Sub(x, tmp), d)
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// a = (a0 + m) // d
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a.Div(tmp.Add(a0, m), d)
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repetend = append(repetend, new(big.Int).Set(a))
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}
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return repetend, nil
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}
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