├── .github └── workflows │ ├── release.yml │ └── vuln-check.yml ├── LICENSE ├── README.md ├── cmd └── viterbiCli │ └── viterbiCli.go ├── go.mod ├── media ├── logo.afdesign ├── logo.svg └── logo_small.svg ├── viterbi.go └── viterbi_test.go /.github/workflows/release.yml: -------------------------------------------------------------------------------- 1 | on: 2 | push: 3 | branches: 4 | - main 5 | name: Build and Release 6 | jobs: 7 | build_and_release: 8 | runs-on: ubuntu-latest 9 | env: # Define environment variables here 10 | TAG: latest 11 | RELEASE_NAME: Latest release 12 | RELEASE_BODY: Latest release 13 | GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} 14 | BINARY_PREFIX: viterbiCli 15 | SOURCE_PATH: cmd/viterbiCli 16 | steps: 17 | - name: Checkout the repository 18 | uses: actions/checkout@v2 19 | - name: Set up Go 20 | uses: actions/setup-go@v2 21 | with: 22 | go-version: '*' # Use the latest stable version of Go 23 | - name: Install dependencies 24 | run: go mod download 25 | - name: Download releaseMaker 26 | run: wget https://github.com/8ff/releaseMaker/releases/download/latest/releaseMaker.linux.amd64 -O /tmp/releaseMaker && chmod +x /tmp/releaseMaker 27 | 28 | - name: Build Darwin ARM64 binary 29 | working-directory: ${{ env.SOURCE_PATH }} 30 | env: 31 | OS: darwin 32 | ARCH: arm64 33 | run: GOOS=$OS GOARCH=$ARCH go build -ldflags "-X 'main.Version=$(date +'%Y-%m-%d_%H:%M:%S')'" -o "/tmp/build/${{ env.BINARY_PREFIX }}.$OS.$ARCH" 34 | 35 | - name: Build Darwin AMD64 binary 36 | working-directory: ${{ env.SOURCE_PATH }} 37 | env: 38 | OS: darwin 39 | ARCH: amd64 40 | run: GOOS=$OS GOARCH=$ARCH go build -ldflags "-X 'main.Version=$(date +'%Y-%m-%d_%H:%M:%S')'" -o "/tmp/build/${{ env.BINARY_PREFIX }}.$OS.$ARCH" 41 | 42 | - name: Build Linux ARM64 binary 43 | working-directory: ${{ env.SOURCE_PATH }} 44 | env: 45 | OS: linux 46 | ARCH: arm64 47 | run: GOOS=$OS GOARCH=$ARCH go build -ldflags "-X 'main.Version=$(date +'%Y-%m-%d_%H:%M:%S')'" -o "/tmp/build/${{ env.BINARY_PREFIX }}.$OS.$ARCH" 48 | 49 | - name: Build Linux AMD64 binary 50 | working-directory: ${{ env.SOURCE_PATH }} 51 | env: 52 | OS: linux 53 | ARCH: amd64 54 | run: GOOS=$OS GOARCH=$ARCH go build -ldflags "-X 'main.Version=$(date +'%Y-%m-%d_%H:%M:%S')'" -o "/tmp/build/${{ env.BINARY_PREFIX }}.$OS.$ARCH" 55 | 56 | - name: Build Windows AMD64 binary 57 | working-directory: ${{ env.SOURCE_PATH }} 58 | env: 59 | OS: windows 60 | ARCH: amd64 61 | run: GOOS=$OS GOARCH=$ARCH go build -ldflags "-X 'main.Version=$(date +'%Y-%m-%d_%H:%M:%S')'" -o "/tmp/build/${{ env.BINARY_PREFIX }}.$OS.$ARCH.exe" 62 | 63 | - name: Build Windows ARM64 binary 64 | working-directory: ${{ env.SOURCE_PATH }} 65 | env: 66 | OS: windows 67 | ARCH: arm64 68 | run: GOOS=$OS GOARCH=$ARCH go build -ldflags "-X 'main.Version=$(date +'%Y-%m-%d_%H:%M:%S')'" -o "/tmp/build/${{ env.BINARY_PREFIX }}.$OS.$ARCH.exe" 69 | 70 | - name: Build OpenBSD AMD64 binary 71 | working-directory: ${{ env.SOURCE_PATH }} 72 | env: 73 | OS: openbsd 74 | ARCH: amd64 75 | run: GOOS=$OS GOARCH=$ARCH go build -ldflags "-X 'main.Version=$(date +'%Y-%m-%d_%H:%M:%S')'" -o "/tmp/build/${{ env.BINARY_PREFIX }}.$OS.$ARCH" 76 | 77 | - name: Build OpenBSD ARM64 binary 78 | working-directory: ${{ env.SOURCE_PATH }} 79 | env: 80 | OS: openbsd 81 | ARCH: arm64 82 | run: GOOS=$OS GOARCH=$ARCH go build -ldflags "-X 'main.Version=$(date +'%Y-%m-%d_%H:%M:%S')'" -o "/tmp/build/${{ env.BINARY_PREFIX }}.$OS.$ARCH" 83 | 84 | - name: Build FreeBSD AMD64 binary 85 | working-directory: ${{ env.SOURCE_PATH }} 86 | env: 87 | OS: freebsd 88 | ARCH: amd64 89 | run: GOOS=$OS GOARCH=$ARCH go build -ldflags "-X 'main.Version=$(date +'%Y-%m-%d_%H:%M:%S')'" -o "/tmp/build/${{ env.BINARY_PREFIX }}.$OS.$ARCH" 90 | 91 | - name: Build FreeBSD ARM64 binary 92 | working-directory: ${{ env.SOURCE_PATH }} 93 | env: 94 | OS: freebsd 95 | ARCH: arm64 96 | run: GOOS=$OS GOARCH=$ARCH go build -ldflags "-X 'main.Version=$(date +'%Y-%m-%d_%H:%M:%S')'" -o "/tmp/build/${{ env.BINARY_PREFIX }}.$OS.$ARCH" 97 | 98 | - name: Build NetBSD AMD64 binary 99 | working-directory: ${{ env.SOURCE_PATH }} 100 | env: 101 | OS: netbsd 102 | ARCH: amd64 103 | run: GOOS=$OS GOARCH=$ARCH go build -ldflags "-X 'main.Version=$(date +'%Y-%m-%d_%H:%M:%S')'" -o "/tmp/build/${{ env.BINARY_PREFIX }}.$OS.$ARCH" 104 | 105 | - name: Build NetBSD ARM64 binary 106 | working-directory: ${{ env.SOURCE_PATH }} 107 | env: 108 | OS: netbsd 109 | ARCH: arm64 110 | run: GOOS=$OS GOARCH=$ARCH go build -ldflags "-X 'main.Version=$(date +'%Y-%m-%d_%H:%M:%S')'" -o "/tmp/build/${{ env.BINARY_PREFIX }}.$OS.$ARCH" 111 | 112 | - name: Build DragonFly BSD AMD64 binary 113 | working-directory: ${{ env.SOURCE_PATH }} 114 | env: 115 | OS: dragonfly 116 | ARCH: amd64 117 | run: GOOS=$OS GOARCH=$ARCH go build -ldflags "-X 'main.Version=$(date +'%Y-%m-%d_%H:%M:%S')'" -o "/tmp/build/${{ env.BINARY_PREFIX }}.$OS.$ARCH" 118 | 119 | - name: Replace Existing Release 120 | run: /tmp/releaseMaker replace ${{ github.repository }} ${{ env.TAG }} "${{ env.RELEASE_NAME }}" "${{ env.RELEASE_BODY }}" 121 | 122 | - name: Upload the artifacts 123 | run: | 124 | cd /tmp/build 125 | for file in *; do 126 | /tmp/releaseMaker upload ${{ github.repository }} ${{ env.TAG }} $file $file 127 | done 128 | -------------------------------------------------------------------------------- /.github/workflows/vuln-check.yml: -------------------------------------------------------------------------------- 1 | name: VulnCheck 2 | on: 3 | pull_request: 4 | branches: 5 | - main 6 | 7 | push: 8 | branches: 9 | - main 10 | 11 | permissions: 12 | contents: read # to fetch code (actions/checkout) 13 | 14 | jobs: 15 | vulncheck: 16 | name: Analysis 17 | runs-on: ubuntu-latest 18 | steps: 19 | - name: Check out code into the Go module directory 20 | uses: actions/checkout@v4 21 | - name: Set up Go 22 | uses: actions/setup-go@v5 23 | with: 24 | go-version: 1.23 25 | - name: Get official govulncheck 26 | run: go install golang.org/x/vuln/cmd/govulncheck@latest 27 | shell: bash 28 | - name: Run govulncheck 29 | run: govulncheck -show verbose ./... 30 | shell: bash 31 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | GNU AFFERO GENERAL PUBLIC LICENSE 2 | Version 3, 19 November 2007 3 | 4 | Copyright (C) 2007 Free Software Foundation, Inc. 5 | Everyone is permitted to copy and distribute verbatim copies 6 | of this license document, but changing it is not allowed. 7 | 8 | Preamble 9 | 10 | The GNU Affero General Public License is a free, copyleft license for 11 | software and other kinds of works, specifically designed to ensure 12 | cooperation with the community in the case of network server software. 13 | 14 | The licenses for most software and other practical works are designed 15 | to take away your freedom to share and change the works. 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Such new versions 565 | will be similar in spirit to the present version, but may differ in detail to 566 | address new problems or concerns. 567 | 568 | Each version is given a distinguishing version number. If the 569 | Program specifies that a certain numbered version of the GNU Affero General 570 | Public License "or any later version" applies to it, you have the 571 | option of following the terms and conditions either of that numbered 572 | version or of any later version published by the Free Software 573 | Foundation. If the Program does not specify a version number of the 574 | GNU Affero General Public License, you may choose any version ever published 575 | by the Free Software Foundation. 576 | 577 | If the Program specifies that a proxy can decide which future 578 | versions of the GNU Affero General Public License can be used, that proxy's 579 | public statement of acceptance of a version permanently authorizes you 580 | to choose that version for the Program. 581 | 582 | Later license versions may give you additional or different 583 | permissions. However, no additional obligations are imposed on any 584 | author or copyright holder as a result of your choosing to follow a 585 | later version. 586 | 587 | 15. Disclaimer of Warranty. 588 | 589 | THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY 590 | APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT 591 | HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY 592 | OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, 593 | THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 594 | PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM 595 | IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF 596 | ALL NECESSARY SERVICING, REPAIR OR CORRECTION. 597 | 598 | 16. Limitation of Liability. 599 | 600 | IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING 601 | WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS 602 | THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY 603 | GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE 604 | USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF 605 | DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD 606 | PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), 607 | EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF 608 | SUCH DAMAGES. 609 | 610 | 17. Interpretation of Sections 15 and 16. 611 | 612 | If the disclaimer of warranty and limitation of liability provided 613 | above cannot be given local legal effect according to their terms, 614 | reviewing courts shall apply local law that most closely approximates 615 | an absolute waiver of all civil liability in connection with the 616 | Program, unless a warranty or assumption of liability accompanies a 617 | copy of the Program in return for a fee. 618 | 619 | END OF TERMS AND CONDITIONS 620 | 621 | How to Apply These Terms to Your New Programs 622 | 623 | If you develop a new program, and you want it to be of the greatest 624 | possible use to the public, the best way to achieve this is to make it 625 | free software which everyone can redistribute and change under these terms. 626 | 627 | To do so, attach the following notices to the program. It is safest 628 | to attach them to the start of each source file to most effectively 629 | state the exclusion of warranty; and each file should have at least 630 | the "copyright" line and a pointer to where the full notice is found. 631 | 632 | 633 | Copyright (C) 634 | 635 | This program is free software: you can redistribute it and/or modify 636 | it under the terms of the GNU Affero General Public License as published 637 | by the Free Software Foundation, either version 3 of the License, or 638 | (at your option) any later version. 639 | 640 | This program is distributed in the hope that it will be useful, 641 | but WITHOUT ANY WARRANTY; without even the implied warranty of 642 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 643 | GNU Affero General Public License for more details. 644 | 645 | You should have received a copy of the GNU Affero General Public License 646 | along with this program. If not, see . 647 | 648 | Also add information on how to contact you by electronic and paper mail. 649 | 650 | If your software can interact with users remotely through a computer 651 | network, you should also make sure that it provides a way for users to 652 | get its source. For example, if your program is a web application, its 653 | interface could display a "Source" link that leads users to an archive 654 | of the code. There are many ways you could offer source, and different 655 | solutions will be better for different programs; see section 13 for the 656 | specific requirements. 657 | 658 | You should also get your employer (if you work as a programmer) or school, 659 | if any, to sign a "copyright disclaimer" for the program, if necessary. 660 | For more information on this, and how to apply and follow the GNU AGPL, see 661 | . 662 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | ![logo](media/logo.svg) 2 | # Convolutional Encoder and Viterbi Decoder 3 | 4 | This package implements a convolutional encoder and a Viterbi decoder. 5 | It can be used as a library or as a command line tool. 6 | 7 | ## Using as a library 8 | ```go 9 | package main 10 | 11 | import ( 12 | "fmt" 13 | "github.com/8ff/viterbi" 14 | ) 15 | 16 | func main() { 17 | // Initialize a codec. 18 | codec, err := viterbi.Init(viterbi.Input{Constraint: 7, Polynomials: []int{91, 109, 121}, ReversePolynomials: false}) 19 | if err != nil { 20 | panic(err) 21 | } 22 | 23 | /**** Encode Bytes ****/ 24 | input := []byte("Hello, world!") 25 | 26 | // Encode a message. 27 | encoded := codec.EncodeBytes(input) 28 | 29 | // Decode the message. 30 | decoded := codec.DecodeBytes(encoded) 31 | 32 | // Print input and decoded message. 33 | fmt.Printf("InputBytes: %s\n", input) 34 | fmt.Printf("DecodedBytes: %s\n", decoded) 35 | 36 | /**** Encode string of bits ****/ 37 | inputBits := "101010" 38 | 39 | // Encode a message. 40 | encodedBits := codec.Encode(inputBits) 41 | 42 | // Decode the message. 43 | decodedBits := codec.Decode(encodedBits) 44 | 45 | // Print input and decoded message. 46 | fmt.Printf("InputBits: %s\n", inputBits) 47 | fmt.Printf("DecodedBits: %s\n", decodedBits) 48 | } 49 | 50 | ``` 51 | 52 | ## Using as command line tool 53 | ```bash 54 | cd cmd/viterbiCli 55 | 56 | # Encode 57 | echo 101010 | go run viterbiCli.go encode 3 5 7 58 | 59 | # Decode 60 | echo 10000010 | go run viterbiCli.go decode 3 5 7 61 | 62 | # Encode/Decode 63 | echo 101010 | go run viterbiCli.go encode 3 5 7 | go run viterbiCli.go decode 3 5 7 64 | ``` 65 | 66 | ## Error Handling 67 | Inputs are validated, and proper error messages will be displayed. 68 | 69 | * The constraint should be greater than 0. 70 | * A generator polynomial should be greater than 0 and less than 1 << constraint. 71 | * The received bit sequence should be of length N * where N is an integer. Otherwise some bits must be missing during transmission. We will fill in appropriate number of trailing zeros. 72 | 73 | ## Dependencies 74 | This code contains no external dependencies. -------------------------------------------------------------------------------- /cmd/viterbiCli/viterbiCli.go: -------------------------------------------------------------------------------- 1 | package main 2 | 3 | import ( 4 | "bufio" 5 | "fmt" 6 | "os" 7 | "strconv" 8 | 9 | "github.com/8ff/viterbi" 10 | ) 11 | 12 | func main() { 13 | args := os.Args 14 | if len(args) < 3 { 15 | fmt.Fprintln(os.Stderr, "Usage: viterbiCli encode/decode ... ") 16 | os.Exit(1) 17 | } 18 | 19 | constraint, err := strconv.Atoi(args[2]) 20 | if err != nil { 21 | fmt.Fprintf(os.Stderr, "Invalid constraint: %s\n", args[2]) 22 | os.Exit(2) 23 | } 24 | 25 | // Read polynomials as remaining arguments except the last one 26 | poly := make([]int, len(args)-4) 27 | for i, p := range args[3 : len(args)-1] { 28 | poly[i], err = strconv.Atoi(p) 29 | if err != nil { 30 | fmt.Fprintf(os.Stderr, "Invalid polynomial: %s\n", p) 31 | os.Exit(2) 32 | } 33 | } 34 | 35 | // Read message from stdin 36 | scanner := bufio.NewScanner(os.Stdin) 37 | scanner.Scan() 38 | message := scanner.Text() 39 | 40 | // fmt.Fprintf(os.Stderr, "constraint: %d, poly: %v, message: %s\n", constraint, poly, message) 41 | 42 | // Init viterbi codec 43 | codec, err := viterbi.Init(viterbi.Input{Constraint: constraint, Polynomials: poly, ReversePolynomials: false}) 44 | if err != nil { 45 | fmt.Fprintln(os.Stderr, err) 46 | os.Exit(3) 47 | } 48 | 49 | // Switch for encode/decode 50 | switch args[1] { 51 | case "encode": 52 | // Encode message 53 | encoded := codec.Encode(message) 54 | 55 | // Print encoded message 56 | fmt.Println(encoded) 57 | case "decode": 58 | // Decode message 59 | decoded := codec.Decode(message) 60 | 61 | // Print decoded message 62 | fmt.Println(decoded) 63 | default: 64 | fmt.Fprintf(os.Stderr, "Invalid command: %s\n", args[1]) 65 | os.Exit(1) 66 | } 67 | } 68 | -------------------------------------------------------------------------------- /go.mod: -------------------------------------------------------------------------------- 1 | module github.com/8ff/viterbi 2 | 3 | go 1.19 4 | -------------------------------------------------------------------------------- /media/logo.afdesign: -------------------------------------------------------------------------------- https://raw.githubusercontent.com/8ff/viterbi/227fdd5e2b34c70778163014515cc148e526daf4/media/logo.afdesign -------------------------------------------------------------------------------- /viterbi.go: -------------------------------------------------------------------------------- 1 | package viterbi 2 | 3 | import ( 4 | "fmt" 5 | "os" 6 | "strconv" 7 | ) 8 | 9 | type Input struct { 10 | Constraint int 11 | Polynomials []int 12 | ReversePolynomials bool 13 | } 14 | 15 | var FLAGS_reverse_polynomials bool 16 | var FLAGS_encode bool 17 | 18 | type Trellis [][]int 19 | 20 | const MaxInt = 1<<(32-1) - 1 21 | 22 | type ViterbiCodec struct { 23 | constraint_ int 24 | polynomials_ []int 25 | outputs_ []string 26 | } 27 | 28 | func (v *ViterbiCodec) num_parity_bits() int { 29 | return len(v.polynomials_) 30 | } 31 | 32 | func (v *ViterbiCodec) NextState(current_state int, input int) int { 33 | return (current_state >> 1) | (input << (v.constraint_ - 2)) 34 | } 35 | 36 | func (v *ViterbiCodec) Output(current_state int, input int) string { 37 | ind := int(current_state | input<<(v.constraint_-1)) 38 | return v.outputs_[ind] 39 | } 40 | 41 | func (v *ViterbiCodec) InitializeOutputs() { 42 | new_len := (1 << v.constraint_) 43 | for i := 0; i < new_len; i++ { 44 | v.outputs_ = append(v.outputs_, "") 45 | 46 | for j := 0; j < v.num_parity_bits(); j++ { 47 | // Reverse polynomial bits to make the convolution code simpler. 48 | polynomial := ReverseBits(v.constraint_, v.polynomials_[j]) 49 | input := i 50 | output := 0 51 | for k := 0; k < v.constraint_; k++ { 52 | output ^= (input & 1) & (polynomial & 1) 53 | polynomial >>= 1 54 | input >>= 1 55 | } 56 | if output == 1 { 57 | v.outputs_[i] += "1" 58 | } else { 59 | v.outputs_[i] += "0" 60 | } 61 | 62 | } 63 | } 64 | 65 | } 66 | 67 | // Encode the given message bits. 68 | func (v *ViterbiCodec) Encode(bits string) string { 69 | state := 0 70 | var encoded string 71 | 72 | // Encode the message bits. 73 | for i := 0; i < len(bits); i++ { 74 | c := bits[i] 75 | input := int(c) - int('0') //c - '0' 76 | 77 | encoded += v.Output(state, input) 78 | 79 | state = v.NextState(state, input) 80 | } 81 | 82 | for i := 0; i < v.constraint_-1; i++ { 83 | encoded += v.Output(state, 0) 84 | state = v.NextState(state, 0) 85 | } 86 | 87 | return encoded 88 | } 89 | 90 | // Return the branch metric for the given source and target states. 91 | func (v *ViterbiCodec) BranchMetric(bits string, source_state int, target_state int) int { 92 | var output string = v.Output(source_state, target_state>>(v.constraint_-2)) 93 | 94 | return HammingDistance(bits, output) 95 | } 96 | 97 | // Return the path metric and the source state for the given target state. 98 | func (v *ViterbiCodec) PathMetric(bits string, prev_path_metrics []int, state int) [2]int { 99 | ret := [2]int{0, 0} 100 | s := (state & ((1 << (v.constraint_ - 2)) - 1)) << 1 101 | source_state1 := s 102 | source_state2 := s | 1 103 | 104 | pm1 := prev_path_metrics[source_state1] 105 | if pm1 < MaxInt { 106 | pm1 += v.BranchMetric(bits, source_state1, state) 107 | } 108 | 109 | pm2 := prev_path_metrics[source_state2] 110 | if pm2 < MaxInt { 111 | pm2 += v.BranchMetric(bits, source_state2, state) 112 | } 113 | 114 | if pm1 <= pm2 { 115 | ret[0] = pm1 116 | ret[1] = source_state1 117 | } else { 118 | ret[0] = pm2 119 | ret[1] = source_state2 120 | } 121 | return (ret) 122 | } 123 | 124 | // Update the path metrics and trellis for the next bit. 125 | func (v *ViterbiCodec) UpdatePathMetrics(bits string, path_metrics []int, trellis Trellis) ([]int, []int) { 126 | var new_path_metrics []int 127 | var new_trellis_column []int 128 | 129 | for w := 0; w < len(path_metrics); w++ { 130 | p := v.PathMetric(bits, path_metrics, w) 131 | new_path_metrics = append(new_path_metrics, p[0]) 132 | new_trellis_column = append(new_trellis_column, p[1]) 133 | } 134 | 135 | return new_path_metrics, new_trellis_column 136 | } 137 | 138 | // Decode a string of bits using the Viterbi algorithm. 139 | func (v *ViterbiCodec) Decode(bits string) string { 140 | var trellis Trellis 141 | var auxTrellis []int 142 | var path_metrics []int 143 | var current_bits string 144 | 145 | for i := 0; i < (1 << (v.constraint_ - 1)); i++ { 146 | path_metrics = append(path_metrics, MaxInt) 147 | } 148 | 149 | path_metrics[0] = 0 150 | for i := 0; i < len(bits); i += v.num_parity_bits() { 151 | 152 | if i+v.num_parity_bits() >= len(bits) { 153 | current_bits = bits[i:] 154 | } else { 155 | current_bits = bits[i : i+v.num_parity_bits()] 156 | } 157 | 158 | // If some bits are missing, fill with trailing zeros. 159 | // This is not ideal but it is the best we can do. 160 | for len(current_bits) < v.num_parity_bits() { 161 | current_bits += "0" 162 | } 163 | 164 | path_metrics, auxTrellis = v.UpdatePathMetrics(current_bits, path_metrics, trellis) 165 | trellis = append(trellis, auxTrellis) 166 | } 167 | 168 | // Traceback. 169 | var decoded string 170 | var state int = findMin(path_metrics) 171 | 172 | for i := len(trellis) - 1; i >= 0; i-- { 173 | 174 | if state>>(v.constraint_-2) == 1 { 175 | decoded += "1" 176 | } else { 177 | decoded += "0" 178 | } 179 | state = trellis[i][state] 180 | 181 | } 182 | 183 | reverse := reverseString(decoded) 184 | return reverse[0 : len(reverse)-v.constraint_+1] 185 | 186 | } 187 | 188 | func reverseString(str string) string { 189 | byte_str := []rune(str) 190 | for i, j := 0, len(byte_str)-1; i < j; i, j = i+1, j-1 { 191 | byte_str[i], byte_str[j] = byte_str[j], byte_str[i] 192 | } 193 | return string(byte_str) 194 | } 195 | 196 | func findMin(v []int) int { 197 | min := v[0] 198 | ind := 0 199 | 200 | for i, value := range v { 201 | if value < min { 202 | min = value 203 | ind = i 204 | } 205 | 206 | } 207 | return ind 208 | } 209 | 210 | func HammingDistance(x string, y string) int { 211 | distance := 0 212 | for i := 0; i < len(x); i++ { 213 | if x[i] != y[i] { 214 | distance += 1 215 | } 216 | } 217 | return distance 218 | } 219 | 220 | func ReverseBits(num_bits int, input int) int { 221 | var output int 222 | output = 0 223 | for i := num_bits - 1; i >= 0; i-- { 224 | output = (output << 1) + (input & 1) 225 | input >>= 1 226 | } 227 | return output 228 | } 229 | 230 | func ParseInt(s string) int { 231 | val, err := strconv.Atoi(s) 232 | if err != nil { 233 | fmt.Printf("Expected a number, found %s\n", s) 234 | os.Exit(0) 235 | } 236 | return val 237 | } 238 | 239 | // Function that takes in []byte and converts it to a string of bits. 240 | func BytesToBits(bytes []byte) string { 241 | var bits string 242 | for _, b := range bytes { 243 | bits += fmt.Sprintf("%08b", b) 244 | } 245 | return bits 246 | } 247 | 248 | // Function that takes in a string of bits and converts it to a []byte. 249 | func BitsToBytes(bits string) []byte { 250 | // Check if the number of bits is a multiple of 8. 251 | if len(bits)%8 != 0 { 252 | return nil 253 | } 254 | 255 | var bytes []byte 256 | for i := 0; i < len(bits); i += 8 { 257 | b, _ := strconv.ParseUint(bits[i:i+8], 2, 8) 258 | bytes = append(bytes, byte(b)) 259 | } 260 | return bytes 261 | } 262 | 263 | func Init(input Input) (*ViterbiCodec, error) { 264 | // Go over polynomials and check if they are valid. 265 | for i := 0; i < len(input.Polynomials); i++ { 266 | if input.Polynomials[i] <= 0 { 267 | return nil, fmt.Errorf("polynomial should be greater than 0, found %d", input.Polynomials[i]) 268 | } 269 | 270 | if input.Polynomials[i] >= (1 << input.Constraint) { 271 | return nil, fmt.Errorf("polynomial should be less than %d found %d", (1 << input.Constraint), input.Polynomials[i]) 272 | } 273 | } 274 | 275 | // Go over polynomials and reverse them if needed. 276 | if input.ReversePolynomials { 277 | for i := 0; i < len(input.Polynomials); i++ { 278 | input.Polynomials[i] = ReverseBits(input.Constraint, input.Polynomials[i]) 279 | } 280 | } 281 | 282 | var codec = ViterbiCodec{constraint_: input.Constraint, polynomials_: input.Polynomials} 283 | codec.InitializeOutputs() 284 | return &codec, nil 285 | } 286 | 287 | // Encode bytes using BytesToBits and run codec.Encode. 288 | func (v *ViterbiCodec) EncodeBytes(bytes []byte) string { 289 | return v.Encode(BytesToBits(bytes)) 290 | } 291 | 292 | // Decode bytes using BitsToBytes and run codec.Decode. 293 | func (v *ViterbiCodec) DecodeBytes(bits string) []byte { 294 | return BitsToBytes(v.Decode(bits)) 295 | } 296 | 297 | // Function that converts a string of bits to []int 298 | func BitsToInts(bits string) []int { 299 | var ints []int 300 | for _, b := range bits { 301 | if b == '0' { 302 | ints = append(ints, 0) 303 | } else { 304 | ints = append(ints, 1) 305 | } 306 | } 307 | return ints 308 | } 309 | 310 | // Function that converts a []int to a string of bits. 311 | func IntsToBits(ints []int) string { 312 | var bits string 313 | for _, i := range ints { 314 | if i == 0 { 315 | bits += "0" 316 | } else { 317 | bits += "1" 318 | } 319 | } 320 | return bits 321 | } 322 | -------------------------------------------------------------------------------- /viterbi_test.go: -------------------------------------------------------------------------------- 1 | package viterbi 2 | 3 | import ( 4 | "bytes" 5 | "math/rand" 6 | "testing" 7 | "time" 8 | ) 9 | 10 | func init() { 11 | // Seed random number generator 12 | rand.Seed(time.Now().UnixNano()) 13 | } 14 | 15 | // Function that takes in a string of 1s and 0s and randomly flips n unique bits. 16 | func corruptBits(bits string, n int) string { 17 | corrupted := []rune(bits) 18 | indices := make(map[int]bool) 19 | for i := 0; i < n; i++ { 20 | // Pick a random index 21 | index := rand.Intn(len(bits)) 22 | // If we've already flipped this bit, pick another index 23 | for indices[index] { 24 | index = rand.Intn(len(bits)) 25 | } 26 | // Flip the bit 27 | if corrupted[index] == '0' { 28 | corrupted[index] = '1' 29 | } else { 30 | corrupted[index] = '0' 31 | } 32 | // Mark this index as flipped 33 | indices[index] = true 34 | } 35 | return string(corrupted) 36 | } 37 | 38 | func TestEncodeDecode(t *testing.T) { 39 | // Vars 40 | constraint := 7 41 | polynomials := []int{91, 109, 121} 42 | inputLen := 20 43 | numOfCorruptBits := 1 44 | reversePolynomials := false 45 | 46 | // Generate random input bytes 47 | inputBytes := make([]byte, inputLen) 48 | for i := 0; i < 6; i++ { 49 | inputBytes[i] = byte(rand.Intn(256)) 50 | } 51 | 52 | codec, err := Init(Input{Constraint: constraint, Polynomials: polynomials, ReversePolynomials: reversePolynomials}) 53 | if err != nil { 54 | t.Fatal(err) 55 | } 56 | 57 | // Encode 58 | encoded := codec.Encode(BytesToBits(inputBytes)) 59 | 60 | // Corrupt bits 61 | encoded = corruptBits(encoded, numOfCorruptBits) 62 | 63 | // Decode 64 | decoded := codec.Decode(encoded) 65 | 66 | // Check if decoded is equal to input 67 | if !bytes.Equal(BitsToBytes(decoded), inputBytes) { 68 | t.Errorf("Expected %s, got %s", BytesToBits(inputBytes), decoded) 69 | } 70 | } 71 | 72 | // Test EncodeDecode 100 times 73 | func TestEncodeDecode100(t *testing.T) { 74 | for i := 0; i < 1000; i++ { 75 | TestEncodeDecode(t) 76 | } 77 | } 78 | 79 | // Test encode/decode using EncodeBytes and DecodeBytes 80 | func TestEncodeDecodeBytes(t *testing.T) { 81 | // Vars 82 | constraint := 7 83 | polynomials := []int{91, 109, 121} 84 | inputLen := 20 85 | numOfCorruptBits := 1 86 | reversePolynomials := false 87 | 88 | // Generate random input bytes 89 | inputBytes := make([]byte, inputLen) 90 | for i := 0; i < 6; i++ { 91 | inputBytes[i] = byte(rand.Intn(256)) 92 | } 93 | 94 | codec, err := Init(Input{Constraint: constraint, Polynomials: polynomials, ReversePolynomials: reversePolynomials}) 95 | if err != nil { 96 | t.Fatal(err) 97 | } 98 | 99 | // Encode 100 | encoded := codec.EncodeBytes(inputBytes) 101 | 102 | // Corrupt bits 103 | encoded = corruptBits(encoded, numOfCorruptBits) 104 | 105 | // Decode 106 | decoded := codec.DecodeBytes(encoded) 107 | 108 | // Check if decoded is equal to input 109 | if !bytes.Equal(decoded, inputBytes) { 110 | t.Errorf("Expected %s, got %s", BytesToBits(inputBytes), decoded) 111 | } 112 | } 113 | 114 | func TestSeparateEncodeDecoders(t *testing.T) { 115 | // Vars 116 | constraint := 7 117 | polynomials := []int{91, 109, 121} 118 | inputLen := 20 119 | numOfCorruptBits := 1 120 | reversePolynomials := false // Somehow when this is true and using different encode/decode codecs, the test fails 121 | 122 | // Generate random input bytes 123 | inputBytes := make([]byte, inputLen) 124 | for i := 0; i < 6; i++ { 125 | inputBytes[i] = byte(rand.Intn(256)) 126 | } 127 | 128 | codec, err := Init(Input{Constraint: constraint, Polynomials: polynomials, ReversePolynomials: reversePolynomials}) 129 | if err != nil { 130 | t.Fatal(err) 131 | } 132 | 133 | // Encode 134 | encoded := codec.Encode(BytesToBits(inputBytes)) 135 | 136 | // Corrupt bits 137 | encoded = corruptBits(encoded, numOfCorruptBits) 138 | 139 | decodeCodec, err := Init(Input{Constraint: constraint, Polynomials: polynomials, ReversePolynomials: reversePolynomials}) 140 | if err != nil { 141 | t.Fatal(err) 142 | } 143 | 144 | // Decode 145 | decoded := decodeCodec.Decode(encoded) 146 | 147 | // Check if decoded is equal to input 148 | if !bytes.Equal(BitsToBytes(decoded), inputBytes) { 149 | t.Errorf("Expected %s, got %s", BytesToBits(inputBytes), decoded) 150 | } 151 | } 152 | --------------------------------------------------------------------------------