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// Copyright 2015 The btcsuite developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.
package btcec
import (
"compress/zlib"
"encoding/base64"
"encoding/binary"
"io/ioutil"
"strings"
)
//go:generate go run -tags gensecp256k1 genprecomps.go
// loadS256BytePoints decompresses and deserializes the pre-computed byte points
// used to accelerate scalar base multiplication for the secp256k1 curve. This
// approach is used since it allows the compile to use significantly less ram
// and be performed much faster than it is with hard-coding the final in-memory
// data structure. At the same time, it is quite fast to generate the in-memory
// data structure at init time with this approach versus computing the table.
func loadS256BytePoints() error {
// There will be no byte points to load when generating them.
bp := secp256k1BytePoints
if len(bp) == 0 {
return nil
}
// Decompress the pre-computed table used to accelerate scalar base
// multiplication.
decoder := base64.NewDecoder(base64.StdEncoding, strings.NewReader(bp))
r, err := zlib.NewReader(decoder)
if err != nil {
return err
}
serialized, err := ioutil.ReadAll(r)
if err != nil {
return err
}
// Deserialize the precomputed byte points and set the curve to them.
offset := 0
var bytePoints [32][256][3]fieldVal
for byteNum := 0; byteNum < 32; byteNum++ {
// All points in this window.
for i := 0; i < 256; i++ {
px := &bytePoints[byteNum][i][0]
py := &bytePoints[byteNum][i][1]
pz := &bytePoints[byteNum][i][2]
for i := 0; i < 10; i++ {
px.n[i] = binary.LittleEndian.Uint32(serialized[offset:])
offset += 4
}
for i := 0; i < 10; i++ {
py.n[i] = binary.LittleEndian.Uint32(serialized[offset:])
offset += 4
}
for i := 0; i < 10; i++ {
pz.n[i] = binary.LittleEndian.Uint32(serialized[offset:])
offset += 4
}
}
}
secp256k1.bytePoints = &bytePoints
return nil
}
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