d891a9c591
Provide default implementations in gf127 package and all optimizations in subpackages. This way it will be easier to use from a client.
61 lines
1.4 KiB
Go
61 lines
1.4 KiB
Go
package gf127
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import (
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"encoding/binary"
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"encoding/hex"
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"errors"
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"math/rand"
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)
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const (
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byteSize = 16
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maxUint64 = ^uint64(0)
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msb64 = uint64(1) << 63
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)
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// GF127 represents element of GF(2^127)
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type GF127 [2]uint64
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// Random returns random element from GF(2^127).
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// Is used mostly for testing.
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func Random() *GF127 {
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return &GF127{rand.Uint64(), rand.Uint64() >> 1}
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}
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// String returns hex-encoded representation, starting with MSB.
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func (c *GF127) String() string {
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return hex.EncodeToString(c.ByteArray())
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}
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// Equals checks if two reduced (zero MSB) elements of GF(2^127) are equal
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func (c *GF127) Equals(b *GF127) bool {
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return c[0] == b[0] && c[1] == b[1]
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}
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// ByteArray represents element of GF(2^127) as byte array of length 16.
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func (c *GF127) ByteArray() (buf []byte) {
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buf = make([]byte, 16)
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binary.BigEndian.PutUint64(buf[:8], c[1])
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binary.BigEndian.PutUint64(buf[8:], c[0])
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return
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}
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// MarshalBinary implements encoding.BinaryMarshaler.
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func (c *GF127) MarshalBinary() (data []byte, err error) {
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return c.ByteArray(), nil
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}
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// UnmarshalBinary implements encoding.BinaryUnmarshaler.
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func (c *GF127) UnmarshalBinary(data []byte) error {
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if len(data) != byteSize {
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return errors.New("data must be 16-bytes long")
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}
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c[0] = binary.BigEndian.Uint64(data[8:])
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c[1] = binary.BigEndian.Uint64(data[:8])
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if c[1]&msb64 != 0 {
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return errors.New("MSB must be zero")
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}
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return nil
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}
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