86 lines
2.3 KiB
Go
86 lines
2.3 KiB
Go
// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// This file contains a straightforward implementation of
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// Reed-Solomon encoding, along with a benchmark.
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// It goes with http://research.swtch.com/field.
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//
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// For an optimized implementation, see gf256.go.
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package gf256
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import (
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"bytes"
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"fmt"
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"testing"
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)
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// BlogECC writes to check the error correcting code bytes
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// for data using the given Reed-Solomon parameters.
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func BlogECC(rs *RSEncoder, m []byte, check []byte) {
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if len(check) < rs.c {
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panic("gf256: invalid check byte length")
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}
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if rs.c == 0 {
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return
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}
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// The check bytes are the remainder after dividing
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// data padded with c zeros by the generator polynomial.
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// p = data padded with c zeros.
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var p []byte
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n := len(m) + rs.c
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if len(rs.p) >= n {
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p = rs.p
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} else {
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p = make([]byte, n)
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}
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copy(p, m)
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for i := len(m); i < len(p); i++ {
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p[i] = 0
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}
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gen := rs.gen
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// Divide p by gen, leaving the remainder in p[len(data):].
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// p[0] is the most significant term in p, and
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// gen[0] is the most significant term in the generator.
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for i := 0; i < len(m); i++ {
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k := f.Mul(p[i], f.Inv(gen[0])) // k = pi / g0
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// p -= k·g
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for j, g := range gen {
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p[i+j] = f.Add(p[i+j], f.Mul(k, g))
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}
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}
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copy(check, p[len(m):])
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rs.p = p
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}
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func BenchmarkBlogECC(b *testing.B) {
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data := []byte{0x10, 0x20, 0x0c, 0x56, 0x61, 0x80, 0xec, 0x11, 0xec, 0x11, 0xec, 0x11, 0xec, 0x11, 0xec, 0x11, 0x10, 0x20, 0x0c, 0x56, 0x61, 0x80, 0xec, 0x11, 0xec, 0x11, 0xec, 0x11, 0xec, 0x11, 0xec, 0x11}
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check := []byte{0x29, 0x41, 0xb3, 0x93, 0x8, 0xe8, 0xa3, 0xe7, 0x63, 0x8f}
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out := make([]byte, len(check))
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rs := NewRSEncoder(f, len(check))
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for i := 0; i < b.N; i++ {
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BlogECC(rs, data, out)
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}
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b.SetBytes(int64(len(data)))
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if !bytes.Equal(out, check) {
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fmt.Printf("have %#v want %#v\n", out, check)
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}
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}
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func TestBlogECC(t *testing.T) {
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data := []byte{0x10, 0x20, 0x0c, 0x56, 0x61, 0x80, 0xec, 0x11, 0xec, 0x11, 0xec, 0x11, 0xec, 0x11, 0xec, 0x11}
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check := []byte{0xa5, 0x24, 0xd4, 0xc1, 0xed, 0x36, 0xc7, 0x87, 0x2c, 0x55}
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out := make([]byte, len(check))
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rs := NewRSEncoder(f, len(check))
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BlogECC(rs, data, out)
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if !bytes.Equal(out, check) {
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t.Errorf("have %x want %x", out, check)
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}
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}
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