├── computation.md ├── README.md ├── webassembly.md ├── runtime.md └── LICENSE /computation.md: -------------------------------------------------------------------------------- 1 | # Computation Strategies 2 | 3 | In this section, we list some common computation strategies for 4 | on-chain processing. 5 | 6 | ## Stop-the-world Computation 7 | 8 | Stop-the-world computation represents a kind of computation where we 9 | need to iterate over the full account list. In this case, because the 10 | account list can be huge, the computation itself is 11 | expensive. However, we must ensure block processing takes minimal time 12 | to ensure network safety and to ensure proof of work cannot be 13 | exploited. There are two methods to do this: 14 | 15 | * **State copying and churn limit**: whenever we need to do 16 | stop-the-world computation, copy the current state into a new 17 | structure, and process accounts with a churn limit. In this way, we 18 | process the whole computation over the span of potentially hundreds 19 | of blocks, which can last a day or two. 20 | * **Data migration**: when an account is touched, process the 21 | computation and migrate the account into a new data structure. In 22 | this way, we always know what accounts are not processed and what 23 | accounts are processed, by checking whether it is in the old or new 24 | data structure. 25 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # Solri Blockchain Experiment 2 | 3 | [![Discord](https://img.shields.io/discord/586902457053872148.svg)](https://discord.gg/DZbg4rZ) 4 | [![Matrix](https://img.shields.io/matrix/solri:matrix.org.svg)](https://riot.im/app/#/room/#solri:matrix.org) 5 | 6 | Solri is a blockchain experiment that tries to bring 7 | [Substrate](https://github.com/paritytech/substrate) style on-chain 8 | governance for Proof of Work. In particular, the design goal is to: 9 | 10 | * Become a **pure** coin, in most possible aspects that blockchain 11 | community cares about. This includes having **no premine** and 12 | establishes **fair launch**. 13 | * Use well-established **Proof of Work** consensus algorithm, and at 14 | the same time, allows it to change to either become ASIC-friendly or 15 | ASIC-resistent. 16 | * Most essential functions of the blockchain is coded into 17 | **WebAssembly** runtime. This makes it so that the blockchain can 18 | evolve and upgrade features **without hard fork**. In fact, we aim 19 | to never conduct any hard fork! 20 | * Have clear and simple **specification** to make supporting multiple 21 | implementations easier. 22 | * Be **stateless**. To fully verify a new block, you will only need 23 | the parent block together with the parent block's runtime 24 | output. This reduces the bare minimal storage requirement for full 25 | node to nearly zero. In practice, clients can selectively choose to 26 | only store states it cares about. 27 | 28 | Before we go on, it is important to note that Solri is currently 29 | entirely a hobby project, and it's really early stage. 30 | 31 | * [Execution Environment and Runtime](./runtime.md) 32 | * [Solri-flavored WebAssembly](./webassembly.md) 33 | -------------------------------------------------------------------------------- /webassembly.md: -------------------------------------------------------------------------------- 1 | # Solri-flavored WebAssembly 2 | 3 | This defines the WebAssembly execution environment for 4 | Solri. Solri-flavored WebAssemly is a subset of WebAssembly that is 5 | deterministic. 6 | 7 | ## Design Principles 8 | 9 | We still aim to maintain WebAssembly's goal of open web platform -- 10 | Solri-flavored WebAssembly maintains to be versionless, 11 | feature-tested, and backward compatible. The WebAssembly execution 12 | environment for Solri is aimed both as the blockchain's specification, 13 | and an efficient implementation. 14 | 15 | We do not define a frozen specification here. Instead, by versionless, 16 | we allow new features to be added onto Solri-flavored WebAssembly, as 17 | long as it remains backward compatible. A feature being added in the 18 | execution environment does not mean it will be used by any runtime. On 19 | the contrary, runtimes are recommended to wait until the majority of 20 | the network upgraded their execution environments, before adopting the 21 | feature. 22 | 23 | In the case when a runtime detects that it requires a feature that the 24 | current execution environment does not support, it must correctly 25 | **trap**. This does make it so that older client might not be able to 26 | execute some runtimes, but it does not result in the classic hard fork 27 | situation where chains can split -- older clients will not be able to 28 | execute any possible blocks on the current runtime, nor build any 29 | blocks. 30 | 31 | ## Value Types 32 | 33 | Solri-flavored WebAssembly supports the following value types: 34 | 35 | * `i32`: 32-bit integer 36 | * `i64`: 64-bit integer 37 | 38 | That is, WebAssembly MVP value types with floating points 39 | disabled. Practically, this means that execution environments should 40 | check that all values in function signatures does not contain floating 41 | point types. 42 | 43 | ## Instructions 44 | 45 | The following instructions are supported in Solri-flavored 46 | WebAssembly: 47 | 48 | * Unreachable 49 | * Nop 50 | * Block(BlockType) 51 | * Loop(BlockType) 52 | * If(BlockType) 53 | * Else 54 | * End 55 | * Br(u32) 56 | * BrIf(u32) 57 | * BrTable(Box) 58 | * Return 59 | * Call(u32) 60 | * CallIndirect(u32 u8) 61 | * Drop 62 | * Select 63 | * GetLocal(u32) 64 | * SetLocal(u32) 65 | * TeeLocal(u32) 66 | * GetGlobal(u32) 67 | * SetGlobal(u32) 68 | * I32Load(u32 u32) 69 | * I64Load(u32 u32) 70 | * I32Load8S(u32 u32) 71 | * I32Load8U(u32 u32) 72 | * I32Load16S(u32 u32) 73 | * I32Load16U(u32 u32) 74 | * I64Load8S(u32 u32) 75 | * I64Load8U(u32 u32) 76 | * I64Load16S(u32 u32) 77 | * I64Load16U(u32 u32) 78 | * I64Load32S(u32 u32) 79 | * I64Load32U(u32 u32) 80 | * I32Store(u32 u32) 81 | * I64Store(u32 u32) 82 | * I32Store8(u32 u32) 83 | * I32Store16(u32 u32) 84 | * I64Store8(u32 u32) 85 | * I64Store16(u32 u32) 86 | * I64Store32(u32 u32) 87 | * CurrentMemory(u8) 88 | * GrowMemory(u8) 89 | * I32Const(i32) 90 | * I64Const(i64) 91 | * I32Eqz 92 | * I32Eq 93 | * I32Ne 94 | * I32LtS 95 | * I32LtU 96 | * I32GtS 97 | * I32GtU 98 | * I32LeS 99 | * I32LeU 100 | * I32GeS 101 | * I32GeU 102 | * I64Eqz 103 | * I64Eq 104 | * I64Ne 105 | * I64LtS 106 | * I64LtU 107 | * I64GtS 108 | * I64GtU 109 | * I64LeS 110 | * I64LeU 111 | * I64GeS 112 | * I64GeU 113 | * I32Clz 114 | * I32Ctz 115 | * I32Popcnt 116 | * I32Add 117 | * I32Sub 118 | * I32Mul 119 | * I32DivS 120 | * I32DivU 121 | * I32RemS 122 | * I32RemU 123 | * I32And 124 | * I32Or 125 | * I32Xor 126 | * I32Shl 127 | * I32ShrS 128 | * I32ShrU 129 | * I32Rotl 130 | * I32Rotr 131 | * I64Clz 132 | * I64Ctz 133 | * I64Popcnt 134 | * I64Add 135 | * I64Sub 136 | * I64Mul 137 | * I64DivS 138 | * I64DivU 139 | * I64RemS 140 | * I64RemU 141 | * I64And 142 | * I64Or 143 | * I64Xor 144 | * I64Shl 145 | * I64ShrS 146 | * I64ShrU 147 | * I64Rotl 148 | * I64Rotr 149 | * I32WrapI64 150 | * I64ExtendSI32 151 | * I64ExtendUI32 152 | 153 | That is, all MVP instructions with floating point instructions 154 | disabled. Practically, this means that the execution environment 155 | should check that none of the floating point instructions exist. 156 | 157 | ## Module Sections 158 | 159 | The following sections are allowed in Solri-flavoured WebAssembly: 160 | 161 | * **import**: Module imports. Linear memory, global variable and 162 | functions are supported. 163 | * **export**: Module exports. Linear memory, global variable and 164 | functions are supported. 165 | * **start**: Module start function. 166 | * **global**: Global section. 167 | * **memory**: Linear memory. 168 | * **data**: Data. 169 | * **function** and **code**: Function and code. 170 | 171 | That is, all MVP sections with table support disabled. 172 | -------------------------------------------------------------------------------- /runtime.md: -------------------------------------------------------------------------------- 1 | # Solri's Runtime 2 | 3 | In this section, we define Solri's execution environment and initial 4 | runtime. 5 | 6 | ## Execution Environment 7 | 8 | The following section defines how the execution environment for Solri 9 | works. 10 | 11 | ### Memory Management 12 | 13 | A WebAssembly instance for Solri is expected to handle its own memory 14 | management. The instance is expected to be long-standing, and might 15 | handle executing multiple blocks. 16 | 17 | First, the guest is expected to export its linear memory. This is to 18 | make it possible that host can read slice of data (blocks, code, and 19 | metadata) from guest. The host will not attempt to allocate any 20 | memory, nor handle any other memory management functionality for the 21 | guest. 22 | 23 | The guest should also exports the following functions: 24 | 25 | * `fn write_code(len: i32) -> i32`: indicates that the host wants to 26 | write the `code` parameter prior of calling `execute` function. The 27 | return value should be the address in guest where host can write the 28 | data slice. 29 | * `fn write_block(len: i32) -> i32`: indicates that the host wants to 30 | write the `block` parameter prior of calling `execute` function. The 31 | return value should be the address in guest where host can write the 32 | data slice. 33 | * `fn read_metadata() -> i32`: available after `execute` is 34 | called. This indicates that the host can read the metadata result of 35 | the block at the given address. 36 | * `fn free()`: frees wrote code, block parameters, and metadata 37 | result, if any. 38 | 39 | ### Block Execution 40 | 41 | This section defines the `execute` export, which exposes the method to 42 | execute a block for a runtime, assuming parent block provided and code 43 | provided is valid, defined as: 44 | 45 | ``` 46 | fn execute() -> i32; 47 | ``` 48 | 49 | Prior of calling this function, the host should first call 50 | `write_code` and `write_block` to feed in the code and block data 51 | slice. If the values are not available, it is an invalid call and the 52 | guest should trap. 53 | 54 | The runtime can change `code` being executed for the next block by 55 | modifying memory location and pass the result values in metadata. The 56 | function returns `-1` if the block is deemed invalid. Otherwise, the 57 | result is `0`. 58 | 59 | If the runtime cannot execute on the current WebAssembly executor, it 60 | should trap (for example, by using the `unreachable` opcode). 61 | 62 | If the execution is successful, the runtime is expected to return the 63 | necessary metadata for the host to further consider the validity of 64 | the block and be able to store it in database. The structure should be 65 | set at `result_ptr`, using C representation: 66 | 67 | ``` 68 | #[repr(C)] 69 | struct Metadata { 70 | timestamp: i64, 71 | difficulty: i64, 72 | 73 | parent_hash_ptr: i32, 74 | parent_hash_len: i32, 75 | 76 | hash_ptr: i32, 77 | hash_len: i32, 78 | 79 | code_ptr: i32, 80 | code_len: i32, 81 | } 82 | ``` 83 | 84 | The full block is up to interpretation of the runtime. The runtime 85 | should return metadata required as defined above. The host can fetch 86 | the metadata using `read_metadata` function. If the execution was 87 | invalid, the host should not assume data under `result_ptr`. 88 | 89 | `execute` should always be used together with memory management 90 | functions. A typical cycle looks like below: 91 | 92 | * Call `write_code` for guest to allocate memory for code data 93 | slice. Then copy code parameter to guest memory. 94 | * Call `write_block` for guest to allocate memory for block data 95 | slice. Then copy block parameter to guest memory. 96 | * Call `execute`. 97 | * Call `read_metadata` if execution was successful, and copy metadata 98 | result from guest back to host. 99 | * Call `free` to deallocate parameters and results. 100 | 101 | ## Timestamp Validation and Fork Choice 102 | 103 | When mining, it is always expected that the miner uses a client whose 104 | native version supports the current WebAssembly runtime. In this case, 105 | the miner should be able to decode `timestamp` from incoming 106 | blocks. The client is then responsible to verify that `timestamp` is 107 | reasonable. The margin is up to each client implementation. When only 108 | validating blocks, one can use the returned metadata to know the 109 | validity of the block, if native version and WebAssembly runtime 110 | mismatches. 111 | 112 | Fork choice rule is defined as choosing the block with the highest 113 | total difficulty. Notice that although we don't limit what the PoW 114 | algorithm is, the fork choice rule is indeed limited by total 115 | difficulty, to ensure backward compatibility. 116 | 117 | ## Initial Runtime and Block Structure 118 | 119 | The actual `runtime` (which exposes `execute`) function is expected to 120 | be stateless. Notice we don't provide any imports for the execution 121 | environment. The initial runtime only supports two operations -- 122 | transfer, and runtime upgrade. 123 | 124 | All below structures are stored in binary merkle tree (`bm` is the 125 | reference implementation), and encoded via SCALE (`parity-codec` is 126 | the reference implementation). 127 | 128 | ### Types and Structures 129 | 130 | We define `State`, which consists of the following structures: 131 | 132 | ``` 133 | type AccountId = u64; 134 | type UpgradeId = u64; 135 | type Balance = u128; 136 | type Nonce = u64; 137 | type Public = H256; 138 | 139 | struct Account { 140 | balance: Balance, 141 | nonce: Nonce, 142 | public: Public 143 | } 144 | 145 | struct Upgrade { 146 | votes: VecArray, 147 | code: Vec, 148 | } 149 | 150 | struct State { 151 | accounts: Vec, 152 | upgrades: Vec, 153 | } 154 | ``` 155 | 156 | The block structures are defined as follows: 157 | 158 | ``` 159 | type Difficulty = u128; 160 | type Timestamp = u64; 161 | type Signature = H512; 162 | type StateProof = bm::CompactValue; 163 | 164 | enum TransferId { 165 | Coinbase, 166 | Existing(AccountId), 167 | New(Public), 168 | } 169 | 170 | enum CoinbaseId { 171 | Existing(AccountId), 172 | New(Public), 173 | } 174 | 175 | enum UnsealedTransaction { 176 | UpgradeProposal { 177 | from: AccountId, 178 | code: Vec, 179 | }, 180 | Transfer { 181 | from: AccountId, 182 | to: Vec<(TransferId, Balance)>, 183 | }, 184 | } 185 | 186 | struct Transaction { 187 | unsealed: UnsealedTransaction, 188 | signature: Signature, 189 | } 190 | 191 | struct UnsealedBlock { 192 | parent_id: Option, 193 | coinbase: CoinbaseId, 194 | timestamp: Timestamp, 195 | difficulty: Difficulty, 196 | state_proof: StateProof, 197 | upgrade_vote: Option, 198 | transactions: Vec, 199 | } 200 | 201 | struct Block { 202 | unsealed: UnsealedBlock, 203 | pow_proof: Vec, 204 | } 205 | ``` 206 | 207 | ### Block Execution 208 | 209 | * **Validity of Proof of Work Proof**: Upon receiving a new block 210 | structure, the executor should first decode `difficulty` and 211 | `timestamp`, and check whether `pow_proof` is valid under the given 212 | difficulty and timestamp. We're still deciding on the actual proof 213 | of work algorithm and difficulty adjustment algorithm. The block 214 | time is tentatively set to one minute. 215 | * **Validity of State Proof**: Given a transaction or a coinbase id, 216 | it is possible to know all the state (defined as generalized merkle 217 | index) it is going to touch. Check all values exist in block's given 218 | state proof. 219 | * **Validity of Transaction Signatures**: Check that 220 | `transaction.from` exists in `state.accounts`, and check that the 221 | `signature` is valid against `state.accounts[i].public`. Increase 222 | `state.accounts[i].nonce` by one. 223 | * **Execution of Transfer Transaction**: Check that `from` account has 224 | balance greater than all `to` amount combined. Transfer value of 225 | `from` into all `to` account, with balance specified as the second 226 | item in the tuple. If `to` is coinbase, transfer to coinbase 227 | account. If `to` is new account, create a new account with all 228 | fields set to `0`, and transfer to the new account. Note that we 229 | don't have the concept of transaction fees -- it is fulfilled by 230 | `coinbase` destination. 231 | * **Execution of Upgrade Proposal Transaction**: Deduct 232 | `PROPOSAL_COST` from `from` account. After that, push `code` as a 233 | new upgrade proposal in `state.upgrades`, and set its `votes` to 234 | `false`. 235 | * **Evaluation of Current Upgrade Proposals**: Iterate over all 236 | `state.upgrades`, shift all `votes` to the right. Push `true` if 237 | `block.upgrade_vote` equals to the proposal index. Otherwise, push 238 | `false`. If a given proposal's `votes` has more than 3072 `true` 239 | (more than 75% of blocks voted for the proposal in the past 4096 240 | blocks), then set the runtime code as in the upgrade proposal. At 241 | this moment, the initial runtime continue its execution, and reaches 242 | its end-of-life after the current block finishes. 243 | * **Block Rewards**: Increase `block.coinbase`'s balance by 244 | `BLOCK_REWARD`. If coinbase points to a new account, create it with 245 | all fields set to `0`. 246 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | GNU GENERAL PUBLIC LICENSE 2 | Version 3, 29 June 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 General Public License is a free, copyleft license for 11 | software and other kinds of works. 12 | 13 | The licenses for most software and other practical works are designed 14 | to take away your freedom to share and change the works. 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Patents. 472 | 473 | A "contributor" is a copyright holder who authorizes use under this 474 | License of the Program or a work on which the Program is based. The 475 | work thus licensed is called the contributor's "contributor version". 476 | 477 | A contributor's "essential patent claims" are all patent claims 478 | owned or controlled by the contributor, whether already acquired or 479 | hereafter acquired, that would be infringed by some manner, permitted 480 | by this License, of making, using, or selling its contributor version, 481 | but do not include claims that would be infringed only as a 482 | consequence of further modification of the contributor version. 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"Knowingly relying" means you have 508 | actual knowledge that, but for the patent license, your conveying the 509 | covered work in a country, or your recipient's use of the covered work 510 | in a country, would infringe one or more identifiable patents in that 511 | country that you have reason to believe are valid. 512 | 513 | If, pursuant to or in connection with a single transaction or 514 | arrangement, you convey, or propagate by procuring conveyance of, a 515 | covered work, and grant a patent license to some of the parties 516 | receiving the covered work authorizing them to use, propagate, modify 517 | or convey a specific copy of the covered work, then the patent license 518 | you grant is automatically extended to all recipients of the covered 519 | work and works based on it. 520 | 521 | A patent license is "discriminatory" if it does not include within 522 | the scope of its coverage, prohibits the exercise of, or is 523 | conditioned on the non-exercise of one or more of the rights that are 524 | specifically granted under this License. You may not convey a covered 525 | work if you are a party to an arrangement with a third party that is 526 | in the business of distributing software, under which you make payment 527 | to the third party based on the extent of your activity of conveying 528 | the work, and under which the third party grants, to any of the 529 | parties who would receive the covered work from you, a discriminatory 530 | patent license (a) in connection with copies of the covered work 531 | conveyed by you (or copies made from those copies), or (b) primarily 532 | for and in connection with specific products or compilations that 533 | contain the covered work, unless you entered into that arrangement, 534 | or that patent license was granted, prior to 28 March 2007. 535 | 536 | Nothing in this License shall be construed as excluding or limiting 537 | any implied license or other defenses to infringement that may 538 | otherwise be available to you under applicable patent law. 539 | 540 | 12. No Surrender of Others' Freedom. 541 | 542 | If conditions are imposed on you (whether by court order, agreement or 543 | otherwise) that contradict the conditions of this License, they do not 544 | excuse you from the conditions of this License. If you cannot convey a 545 | covered work so as to satisfy simultaneously your obligations under this 546 | License and any other pertinent obligations, then as a consequence you may 547 | not convey it at all. For example, if you agree to terms that obligate you 548 | to collect a royalty for further conveying from those to whom you convey 549 | the Program, the only way you could satisfy both those terms and this 550 | License would be to refrain entirely from conveying the Program. 551 | 552 | 13. Use with the GNU Affero General Public License. 553 | 554 | Notwithstanding any other provision of this License, you have 555 | permission to link or combine any covered work with a work licensed 556 | under version 3 of the GNU Affero General Public License into a single 557 | combined work, and to convey the resulting work. The terms of this 558 | License will continue to apply to the part which is the covered work, 559 | but the special requirements of the GNU Affero General Public License, 560 | section 13, concerning interaction through a network will apply to the 561 | combination as such. 562 | 563 | 14. Revised Versions of this License. 564 | 565 | The Free Software Foundation may publish revised and/or new versions of 566 | the GNU General Public License from time to time. Such new versions will 567 | be similar in spirit to the present version, but may differ in detail to 568 | address new problems or concerns. 569 | 570 | Each version is given a distinguishing version number. If the 571 | Program specifies that a certain numbered version of the GNU General 572 | Public License "or any later version" applies to it, you have the 573 | option of following the terms and conditions either of that numbered 574 | version or of any later version published by the Free Software 575 | Foundation. If the Program does not specify a version number of the 576 | GNU General Public License, you may choose any version ever published 577 | by the Free Software Foundation. 578 | 579 | If the Program specifies that a proxy can decide which future 580 | versions of the GNU General Public License can be used, that proxy's 581 | public statement of acceptance of a version permanently authorizes you 582 | to choose that version for the Program. 583 | 584 | Later license versions may give you additional or different 585 | permissions. However, no additional obligations are imposed on any 586 | author or copyright holder as a result of your choosing to follow a 587 | later version. 588 | 589 | 15. Disclaimer of Warranty. 590 | 591 | THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY 592 | APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT 593 | HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY 594 | OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, 595 | THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 596 | PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM 597 | IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF 598 | ALL NECESSARY SERVICING, REPAIR OR CORRECTION. 599 | 600 | 16. Limitation of Liability. 601 | 602 | IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING 603 | WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS 604 | THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY 605 | GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE 606 | USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF 607 | DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD 608 | PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), 609 | EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF 610 | SUCH DAMAGES. 611 | 612 | 17. Interpretation of Sections 15 and 16. 613 | 614 | If the disclaimer of warranty and limitation of liability provided 615 | above cannot be given local legal effect according to their terms, 616 | reviewing courts shall apply local law that most closely approximates 617 | an absolute waiver of all civil liability in connection with the 618 | Program, unless a warranty or assumption of liability accompanies a 619 | copy of the Program in return for a fee. 620 | 621 | END OF TERMS AND CONDITIONS 622 | 623 | How to Apply These Terms to Your New Programs 624 | 625 | If you develop a new program, and you want it to be of the greatest 626 | possible use to the public, the best way to achieve this is to make it 627 | free software which everyone can redistribute and change under these terms. 628 | 629 | To do so, attach the following notices to the program. It is safest 630 | to attach them to the start of each source file to most effectively 631 | state the exclusion of warranty; and each file should have at least 632 | the "copyright" line and a pointer to where the full notice is found. 633 | 634 | 635 | Copyright (C) 636 | 637 | This program is free software: you can redistribute it and/or modify 638 | it under the terms of the GNU General Public License as published by 639 | the Free Software Foundation, either version 3 of the License, or 640 | (at your option) any later version. 641 | 642 | This program is distributed in the hope that it will be useful, 643 | but WITHOUT ANY WARRANTY; without even the implied warranty of 644 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 645 | GNU General Public License for more details. 646 | 647 | You should have received a copy of the GNU General Public License 648 | along with this program. If not, see . 649 | 650 | Also add information on how to contact you by electronic and paper mail. 651 | 652 | If the program does terminal interaction, make it output a short 653 | notice like this when it starts in an interactive mode: 654 | 655 | Copyright (C) 656 | This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'. 657 | This is free software, and you are welcome to redistribute it 658 | under certain conditions; type `show c' for details. 659 | 660 | The hypothetical commands `show w' and `show c' should show the appropriate 661 | parts of the General Public License. Of course, your program's commands 662 | might be different; for a GUI interface, you would use an "about box". 663 | 664 | You should also get your employer (if you work as a programmer) or school, 665 | if any, to sign a "copyright disclaimer" for the program, if necessary. 666 | For more information on this, and how to apply and follow the GNU GPL, see 667 | . 668 | 669 | The GNU General Public License does not permit incorporating your program 670 | into proprietary programs. If your program is a subroutine library, you 671 | may consider it more useful to permit linking proprietary applications with 672 | the library. If this is what you want to do, use the GNU Lesser General 673 | Public License instead of this License. But first, please read 674 | . 675 | --------------------------------------------------------------------------------