status-im/status-go

package identity

import (
    "errors"
    "fmt"
    "math/big"
    "testing"

    "github.com/ethereum/go-ethereum/crypto/secp256k1"
)

func ToColorID(pubkey string) (int64, error) {
    const colorPalletLength = 12

    pubkeyValue, ok := new(big.Int).SetString(pubkey, 0)
    if !ok {
        return 0, fmt.Errorf("invalid pubkey: %s", pubkey)
    }

    colorID := new(big.Int).Mod(pubkeyValue, new(big.Int).SetInt64(colorPalletLength-1)).Int64()

    return colorID, nil
}

func ToBigBase(value *big.Int, base uint64) (res [](uint64)) {
    toBigBaseImpl(value, base, &res)
    return
}

func toBigBaseImpl(value *big.Int, base uint64, res *[](uint64)) {
    bigBase := new(big.Int).SetUint64(base)
    quotient := new(big.Int).Div(value, bigBase)
    if quotient.Cmp(new(big.Int).SetUint64(0)) != 0 {
        toBigBaseImpl(quotient, base, res)
    }

    *res = append(*res, new(big.Int).Mod(value, bigBase).Uint64())
}

// compressedPubKey = |1.5 bytes chars cutoff|20 bytes emoji hash|10 bytes color hash|1.5 bytes chars cutoff|
func Slices(compressedPubkey []byte) (res [4][]byte, err error) {
    if len(compressedPubkey) != 33 {
        return res, errors.New("incorrect compressed pubkey")
    }

    getSlice := func(low, high int, and string, rsh uint) []byte {
        sliceValue := new(big.Int).SetBytes(compressedPubkey[low:high])
        andValue, _ := new(big.Int).SetString(and, 0)
        andRes := new(big.Int).And(sliceValue, andValue)
        return new(big.Int).Rsh(andRes, rsh).Bytes()
    }

    res[0] = getSlice(0, 2, "0xFFF0", 4)
    res[1] = getSlice(1, 22, "0x0FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF0", 4)
    res[2] = getSlice(21, 32, "0x0FFFFFFFFFFFFFFFFFFFF0", 4)
    res[3] = getSlice(31, 33, "0x0FFF", 0)

    return res, nil
}

func ToCompressedKey(pubkey string) ([]byte, error) {
    pubkeyValue, ok := new(big.Int).SetString(pubkey, 0)
    if !ok {
        return nil, fmt.Errorf("invalid pubkey: %s", pubkey)
    }

    x, y := secp256k1.S256().Unmarshal(pubkeyValue.Bytes())
    if x == nil || !secp256k1.S256().IsOnCurve(x, y) {
        return nil, fmt.Errorf("invalid pubkey: %s", pubkey)
    }

    return secp256k1.CompressPubkey(x, y), nil
}

func ToBigInt(t *testing.T, str string) *big.Int {
    res, ok := new(big.Int).SetString(str, 0)
    if !ok {
        t.Errorf("invalid conversion to int from %s", str)
    }
    return res
}