36 lines
662 B
Go
36 lines
662 B
Go
package bls12381
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import (
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"math/big"
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)
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func wnaf(e0 *big.Int, window uint) []int64 {
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e := new(big.Int).Set(e0)
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zero := big.NewInt(0)
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if e.Cmp(zero) == 0 {
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return []int64{}
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}
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max := int64(1 << window)
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midpoint := int64(1 << (window - 1))
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modulusMask := uint64(1<<window) - 1
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var out []int64
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for e.Cmp(zero) != 0 {
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var z int64
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if e.Bit(0)&1 == 1 {
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maskedBits := int64(e.Uint64() & modulusMask)
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if maskedBits > midpoint {
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z = maskedBits - max
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e.Add(e, new(big.Int).SetInt64(0-z))
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} else {
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z = maskedBits
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e.Sub(e, new(big.Int).SetInt64(z))
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}
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} else {
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z = 0
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}
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out = append(out, z)
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e.Rsh(e, 1)
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}
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return out
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}
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