The Portable Document Format (PDF) is a file format developed by Adobe in the s to present documents, including text formatting and images, in a manner. Wikipedia pages can be exported and saved as PDF files. From the left sidebar , under Print/export, select Download as PDF. The rendering engine starts and. Size of this JPG preview of this PDF file: × pixels. Original file (1, × 1, pixels, file size: 16 KB, MIME type: application/pdf).
|Language:||English, Spanish, Dutch|
|Distribution:||Free* [*Register to download]|
Media in category "PDF icons". The following 72 files are in this category, out of 72 total. compgarbullkunsbar.cf 15 × 18; bytes. Size of this JPG preview of this PDF file: × pixels. Other resolutions: Original file (1, × 1, pixels, file size: KB, MIME type: application/pdf). Size of this JPG preview of this PDF file: × pixels. Other resolutions: uses this file: File:Wikipedia - OpenStreetMap compgarbullkunsbar.cf (file redirect).
The tags view is what screen readers and other assistive technologies use to deliver a high-quality navigation and reading experience to users with disabilities. The content view is based on the physical order of objects within the PDF's content stream and may be displayed by software that does not fully support the tags view, such as the Reflow feature in Adobe's Reader. It was activated with Adobe Acrobat, but not with Acrobat Reader.
Other PDF readers are also susceptible. One aggravating factor is that a PDF reader can be configured to start automatically if a web page has an embedded PDF file, providing a vector for attack. If a malicious web page contains an infected PDF file that takes advantage of a vulnerability in the PDF reader, the system may be compromised even if the browser is secure.
The basic types of content in a PDF are: Text stored as content streams i. PDF 1. For example, a high resolution raster image takes more space than a low resolution one. Typically higher resolution is needed for printing documents than for displaying them on screen.
Other things that may increase the size of a file is embedding full fonts, especially for Asiatic scripts, and storing text as graphics. For a more comprehensive list, see List of PDF software. PDF viewers are generally provided free of charge, and many versions are available from a variety of sources.
Raster image processors RIPs are used to convert PDF files into a raster format suitable for imaging onto paper and other media in printers, digital production presses and prepress in a process known as rasterisation. To enable it, scroll to the bottom of the page and select Desktop.
To view the PDF you must have a browser that directly supports PDF viewing or an application installed on your computer. From Wikipedia, the free encyclopedia. This help page is a how-to guide. It details processes or procedures of some aspect s of Wikipedia's norms and practices. It is not one of Wikipedia's policies or guidelines , as it has not been thoroughly vetted by the community.
For more information, see the list of bugs on Phabricator. Wikipedia technical help. Set it up as an Ethereum contract. Want to set up a full-scale Daemon or Skynet? You may need to have a few thousand interlocking contracts, and be sure to feed them generously, to do that, but nothing is stopping you with Ethereum at your fingertips. Modularity: the parts of the Ethereum protocol should be designed to be as modular and separable as possible.
Over the course of development, our goal is to create a program where if one was to make a small protocol modification in one place, the application stack would continue to function without any further modification. This is so that even though they are used in Ethereum, even if Ethereum does not require certain features, such features are still usable in other protocols as well. Ethereum development should be maximally done so as to benefit the entire cryptocurrency ecosystem, not just itself.
Agility: details of the Ethereum protocol are not set in stone. Although we will be extremely judicious about making modifications to high-level constructs, for instance with the sharding roadmap , abstracting execution, with only data availability enshrined in consensus. Computational tests later on in the development process may lead us to discover that certain modifications, e.
If any such opportunities are found, we will exploit them. Non-discrimination and non-censorship: the protocol should not attempt to actively restrict or prevent specific categories of usage. All regulatory mechanisms in the protocol should be designed to directly regulate the harm and not attempt to oppose specific undesirable applications. A programmer can even run an infinite loop script on top of Ethereum for as long as they are willing to keep paying the per-computational-step transaction fee.
Ethereum Accounts In Ethereum, the state is made up of objects called "accounts", with each account having a byte address and state transitions being direct transfers of value and information between accounts. An Ethereum account contains four fields: The nonce, a counter used to make sure each transaction can only be processed once The account's current ether balance The account's contract code, if present The account's storage empty by default "Ether" is the main internal crypto-fuel of Ethereum, and is used to pay transaction fees.
In general, there are two types of accounts: externally owned accounts, controlled by private keys, and contract accounts, controlled by their contract code. An externally owned account has no code, and one can send messages from an externally owned account by creating and signing a transaction; in a contract account, every time the contract account receives a message its code activates, allowing it to read and write to internal storage and send other messages or create contracts in turn.
Messages and Transactions The term "transaction" is used in Ethereum to refer to the signed data package that stores a message to be sent from an externally owned account. Transactions contain: The recipient of the message A signature identifying the sender The amount of ether to transfer from the sender to the recipient An optional data field A STARTGAS value, representing the maximum number of computational steps the transaction execution is allowed to take A GASPRICE value, representing the fee the sender pays per computational step The first three are standard fields expected in any cryptocurrency.
The data field has no function by default, but the virtual machine has an opcode which a contract can use to access the data; as an example use case, if a contract is functioning as an on-blockchain domain registration service, then it may wish to interpret the data being passed to it as containing two "fields", the first field being a domain to register and the second field being the IP address to register it to.
The contract would read these values from the message data and appropriately place them in storage. In order to prevent accidental or hostile infinite loops or other computational wastage in code, each transaction is required to set a limit to how many computational steps of code execution it can use.
The fundamental unit of computation is "gas"; usually, a computational step costs 1 gas, but some operations cost higher amounts of gas because they are more computationally expensive, or increase the amount of data that must be stored as part of the state. There is also a fee of 5 gas for every byte in the transaction data. The intent of the fee system is to require an attacker to pay proportionately for every resource that they consume, including computation, bandwidth and storage; hence, any transaction that leads to the network consuming a greater amount of any of these resources must have a gas fee roughly proportional to the increment.
Messages Contracts have the ability to send "messages" to other contracts. Messages are virtual objects that are never serialized and exist only in the Ethereum execution environment. A message contains: The sender of the message implicit The recipient of the message The amount of ether to transfer alongside the message An optional data field A STARTGAS value Essentially, a message is like a transaction, except it is produced by a contract and not an external actor.
A message is produced when a contract currently executing code executes the CALL opcode, which produces and executes a message. Like a transaction, a message leads to the recipient account running its code.
Thus, contracts can have relationships with other contracts in exactly the same way that external actors can. Note that the gas allowance assigned by a transaction or contract applies to the total gas consumed by that transaction and all sub-executions. For example, if an external actor A sends a transaction to B with gas, and B consumes gas before sending a message to C, and the internal execution of C consumes gas before returning, then B can spend another gas before running out of gas.
If not, return an error. Subtract the fee from the sender's account balance and increment the sender's nonce. If there is not enough balance to spend, return an error. Transfer the transaction value from the sender's account to the receiving account. If the receiving account does not yet exist, create it. If the receiving account is a contract, run the contract's code either to completion or until the execution runs out of gas.
If the value transfer failed because the sender did not have enough money, or the code execution ran out of gas, revert all state changes except the payment of the fees, and add the fees to the miner's account. Otherwise, refund the fees for all remaining gas to the sender, and send the fees paid for gas consumed to the miner.
For example, suppose that the contract's code is: if! Suppose that the contract's storage starts off empty, and a transaction is sent with 10 ether value, gas, 0. If it is, then subtract 2 ether from the sender's account. Subtract 10 more ether from the sender's account, and add it to the contract's account.
Run the code. In this case, this is simple: it checks if the contract's storage at index 2 is used, notices that it is not, and so it sets the storage at index 2 to the value CHARLIE. If there was no contract at the receiving end of the transaction, then the total transaction fee would simply be equal to the provided GASPRICE multiplied by the length of the transaction in bytes, and the data sent alongside the transaction would be irrelevant.
Note that messages work equivalently to transactions in terms of reverts: if a message execution runs out of gas, then that message's execution, and all other executions triggered by that execution, revert, but parent executions do not need to revert.
This means that it is "safe" for a contract to call another contract, as if A calls B with G gas then A's execution is guaranteed to lose at most G gas. Finally, note that there is an opcode, CREATE, that creates a contract; its execution mechanics are generally similar to CALL, with the exception that the output of the execution determines the code of a newly created contract. Code Execution The code in Ethereum contracts is written in a low-level, stack-based bytecode language, referred to as "Ethereum virtual machine code" or "EVM code".
The code consists of a series of bytes, where each byte represents an operation. In general, code execution is an infinite loop that consists of repeatedly carrying out the operation at the current program counter which begins at zero and then incrementing the program counter by one, until the end of the code is reached or an error or STOP or RETURN instruction is detected.
Unlike stack and memory, which reset after computation ends, storage persists for the long term. The code can also access the value, sender and data of the incoming message, as well as block header data, and the code can also return a byte array of data as an output.
The formal execution model of EVM code is surprisingly simple. For example, ADD pops two items off the stack and pushes their sum, reduces gas by 1 and increments pc by 1, and SSTORE pops the top two items off the stack and inserts the second item into the contract's storage at the index specified by the first item.
Although there are many ways to optimize Ethereum virtual machine execution via just-in-time compilation, a basic implementation of Ethereum can be done in a few hundred lines of code. Blockchain and Mining.